Encoder API - jxl/encode.h

group libjxl_encoder

Typedefs

typedef struct JxlEncoderStruct JxlEncoder

Opaque structure that holds the JPEG XL encoder.

Allocated and initialized with JxlEncoderCreate(). Cleaned up and deallocated with JxlEncoderDestroy().

typedef struct JxlEncoderFrameSettingsStruct JxlEncoderFrameSettings

Settings and metadata for a single image frame. This includes encoder options for a frame such as compression quality and speed.

Allocated and initialized with JxlEncoderFrameSettingsCreate(). Cleaned up and deallocated when the encoder is destroyed with JxlEncoderDestroy().

typedef void (*JxlDebugImageCallback)(void *opaque, const char *label, size_t xsize, size_t ysize, const JxlColorEncoding *color, const uint16_t *pixels)

Function type for JxlEncoderSetDebugImageCallback.

The callback may be called simultaneously by different threads when using a threaded parallel runner, on different debug images.

Param opaque:

optional user data, as given to JxlEncoderSetDebugImageCallback.

Param label:

label of debug image, can be used in filenames

Param xsize:

width of debug image

Param ysize:

height of debug image

Param color:

color encoding of debug image

Param pixels:

pixel data of debug image as big-endian 16-bit unsigned samples. The memory is not owned by the user, and is only valid during the time the callback is running.

typedef struct JxlEncoderStatsStruct JxlEncoderStats

Opaque structure that holds the encoder statistics.

Allocated and initialized with JxlEncoderStatsCreate(). Cleaned up and deallocated with JxlEncoderStatsDestroy().

Enums

enum JxlEncoderStatus

Return value for multiple encoder functions.

Values:

enumerator JXL_ENC_SUCCESS

Function call finished successfully, or encoding is finished and there is nothing more to be done.

enumerator JXL_ENC_ERROR

An error occurred, for example out of memory.

enumerator JXL_ENC_NEED_MORE_OUTPUT

The encoder needs more output buffer to continue encoding.

enum JxlEncoderError

Error conditions: API usage errors have the 0x80 bit set to 1 Other errors have the 0x80 bit set to 0

Values:

enumerator JXL_ENC_ERR_OK

No error

enumerator JXL_ENC_ERR_GENERIC

Generic encoder error due to unspecified cause

enumerator JXL_ENC_ERR_OOM

Out of memory TODO(jon): actually catch this and return this error

enumerator JXL_ENC_ERR_JBRD

JPEG bitstream reconstruction data could not be represented (e.g. too much tail data)

enumerator JXL_ENC_ERR_BAD_INPUT

Input is invalid (e.g. corrupt JPEG file or ICC profile)

enumerator JXL_ENC_ERR_NOT_SUPPORTED

The encoder doesn’t (yet) support this. Either no version of libjxl supports this, and the API is used incorrectly, or the libjxl version should have been checked before trying to do this.

enumerator JXL_ENC_ERR_API_USAGE

The encoder API is used in an incorrect way. In this case, a debug build of libjxl should output a specific error message. (if not, please open an issue about it)

enum JxlEncoderFrameSettingId

Id of encoder options for a frame. This includes options such as setting encoding effort/speed or overriding the use of certain coding tools, for this frame. This does not include non-frame related encoder options such as for boxes.

Values:

enumerator JXL_ENC_FRAME_SETTING_EFFORT

Sets encoder effort/speed level without affecting decoding speed. Valid values are, from faster to slower speed: 1:lightning 2:thunder 3:falcon 4:cheetah 5:hare 6:wombat 7:squirrel 8:kitten 9:tortoise 10:glacier. Default: squirrel (7).

enumerator JXL_ENC_FRAME_SETTING_DECODING_SPEED

Sets the decoding speed tier for the provided options. Minimum is 0 (slowest to decode, best quality/density), and maximum is 4 (fastest to decode, at the cost of some quality/density). Default is 0.

enumerator JXL_ENC_FRAME_SETTING_RESAMPLING

Sets resampling option. If enabled, the image is downsampled before compression, and upsampled to original size in the decoder. Integer option, use -1 for the default behavior (resampling only applied for low quality), 1 for no downsampling (1x1), 2 for 2x2 downsampling, 4 for 4x4 downsampling, 8 for 8x8 downsampling.

enumerator JXL_ENC_FRAME_SETTING_EXTRA_CHANNEL_RESAMPLING

Similar to JXL_ENC_FRAME_SETTING_RESAMPLING, but for extra channels. Integer option, use -1 for the default behavior (depends on encoder implementation), 1 for no downsampling (1x1), 2 for 2x2 downsampling, 4 for 4x4 downsampling, 8 for 8x8 downsampling.

enumerator JXL_ENC_FRAME_SETTING_ALREADY_DOWNSAMPLED

Indicates the frame added with JxlEncoderAddImageFrame is already downsampled by the downsampling factor set with JXL_ENC_FRAME_SETTING_RESAMPLING. The input frame must then be given in the downsampled resolution, not the full image resolution. The downsampled resolution is given by ceil(xsize / resampling), ceil(ysize / resampling) with xsize and ysize the dimensions given in the basic info, and resampling the factor set with JXL_ENC_FRAME_SETTING_RESAMPLING. Use 0 to disable, 1 to enable. Default value is 0.

enumerator JXL_ENC_FRAME_SETTING_PHOTON_NOISE

Adds noise to the image emulating photographic film noise, the higher the given number, the grainier the image will be. As an example, a value of 100 gives low noise whereas a value of 3200 gives a lot of noise. The default value is 0.

enumerator JXL_ENC_FRAME_SETTING_NOISE

Enables adaptive noise generation. This setting is not recommended for use, please use JXL_ENC_FRAME_SETTING_PHOTON_NOISE instead. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_DOTS

Enables or disables dots generation. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_PATCHES

Enables or disables patches generation. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_EPF

Edge preserving filter level, -1 to 3. Use -1 for the default (encoder chooses), 0 to 3 to set a strength.

enumerator JXL_ENC_FRAME_SETTING_GABORISH

Enables or disables the gaborish filter. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_MODULAR

Enables modular encoding. Use -1 for default (encoder chooses), 0 to enforce VarDCT mode (e.g. for photographic images), 1 to enforce modular mode (e.g. for lossless images).

enumerator JXL_ENC_FRAME_SETTING_KEEP_INVISIBLE

Enables or disables preserving color of invisible pixels. Use -1 for the default (1 if lossless, 0 if lossy), 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_GROUP_ORDER

Determines the order in which 256x256 regions are stored in the codestream for progressive rendering. Use -1 for the encoder default, 0 for scanline order, 1 for center-first order.

enumerator JXL_ENC_FRAME_SETTING_GROUP_ORDER_CENTER_X

Determines the horizontal position of center for the center-first group order. Use -1 to automatically use the middle of the image, 0..xsize to specifically set it.

enumerator JXL_ENC_FRAME_SETTING_GROUP_ORDER_CENTER_Y

Determines the center for the center-first group order. Use -1 to automatically use the middle of the image, 0..ysize to specifically set it.

enumerator JXL_ENC_FRAME_SETTING_RESPONSIVE

Enables or disables progressive encoding for modular mode. Use -1 for the encoder default, 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_PROGRESSIVE_AC

Set the progressive mode for the AC coefficients of VarDCT, using spectral progression from the DCT coefficients. Use -1 for the encoder default, 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_QPROGRESSIVE_AC

Set the progressive mode for the AC coefficients of VarDCT, using quantization of the least significant bits. Use -1 for the encoder default, 0 to disable, 1 to enable.

enumerator JXL_ENC_FRAME_SETTING_PROGRESSIVE_DC

Set the progressive mode using lower-resolution DC images for VarDCT. Use -1 for the encoder default, 0 to disable, 1 to have an extra 64x64 lower resolution pass, 2 to have a 512x512 and 64x64 lower resolution pass.

enumerator JXL_ENC_FRAME_SETTING_CHANNEL_COLORS_GLOBAL_PERCENT

Use Global channel palette if the amount of colors is smaller than this percentage of range. Use 0-100 to set an explicit percentage, -1 to use the encoder default. Used for modular encoding.

enumerator JXL_ENC_FRAME_SETTING_CHANNEL_COLORS_GROUP_PERCENT

Use Local (per-group) channel palette if the amount of colors is smaller than this percentage of range. Use 0-100 to set an explicit percentage, -1 to use the encoder default. Used for modular encoding.

enumerator JXL_ENC_FRAME_SETTING_PALETTE_COLORS

Use color palette if amount of colors is smaller than or equal to this amount, or -1 to use the encoder default. Used for modular encoding.

enumerator JXL_ENC_FRAME_SETTING_LOSSY_PALETTE

Enables or disables delta palette. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable. Used in modular mode.

enumerator JXL_ENC_FRAME_SETTING_COLOR_TRANSFORM

Color transform for internal encoding: -1 = default, 0=XYB, 1=none (RGB), 2=YCbCr. The XYB setting performs the forward XYB transform. None and YCbCr both perform no transform, but YCbCr is used to indicate that the encoded data losslessly represents YCbCr values.

enumerator JXL_ENC_FRAME_SETTING_MODULAR_COLOR_SPACE

Reversible color transform for modular encoding: -1=default, 0-41=RCT index, e.g. index 0 = none, index 6 = YCoCg. If this option is set to a non-default value, the RCT will be globally applied to the whole frame. The default behavior is to try several RCTs locally per modular group, depending on the speed and distance setting.

enumerator JXL_ENC_FRAME_SETTING_MODULAR_GROUP_SIZE

Group size for modular encoding: -1=default, 0=128, 1=256, 2=512, 3=1024.

enumerator JXL_ENC_FRAME_SETTING_MODULAR_PREDICTOR

Predictor for modular encoding. -1 = default, 0=zero, 1=left, 2=top, 3=avg0, 4=select, 5=gradient, 6=weighted, 7=topright, 8=topleft, 9=leftleft, 10=avg1, 11=avg2, 12=avg3, 13=toptop predictive average 14=mix 5 and 6, 15=mix everything.

enumerator JXL_ENC_FRAME_SETTING_MODULAR_MA_TREE_LEARNING_PERCENT

Fraction of pixels used to learn MA trees as a percentage. -1 = default, 0 = no MA and fast decode, 50 = default value, 100 = all, values above 100 are also permitted. Higher values use more encoder memory.

enumerator JXL_ENC_FRAME_SETTING_MODULAR_NB_PREV_CHANNELS

Number of extra (previous-channel) MA tree properties to use. -1 = default, 0-11 = valid values. Recommended values are in the range 0 to 3, or 0 to amount of channels minus 1 (including all extra channels, and excluding color channels when using VarDCT mode). Higher value gives slower encoding and slower decoding.

enumerator JXL_ENC_FRAME_SETTING_JPEG_RECON_CFL

Enable or disable CFL (chroma-from-luma) for lossless JPEG recompression. -1 = default, 0 = disable CFL, 1 = enable CFL.

enumerator JXL_ENC_FRAME_INDEX_BOX

Prepare the frame for indexing in the frame index box. 0 = ignore this frame (same as not setting a value), 1 = index this frame within the Frame Index Box. If any frames are indexed, the first frame needs to be indexed, too. If the first frame is not indexed, and a later frame is attempted to be indexed, JXL_ENC_ERROR will occur. If non-keyframes, i.e., frames with cropping, blending or patches are attempted to be indexed, JXL_ENC_ERROR will occur.

enumerator JXL_ENC_FRAME_SETTING_BROTLI_EFFORT

Sets brotli encode effort for use in JPEG recompression and compressed metadata boxes (brob). Can be -1 (default) or 0 (fastest) to 11 (slowest). Default is based on the general encode effort in case of JPEG recompression, and 4 for brob boxes.

enumerator JXL_ENC_FRAME_SETTING_JPEG_COMPRESS_BOXES

Enables or disables brotli compression of metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. -1 = default, 0 = disable compression, 1 = enable compression.

enumerator JXL_ENC_FRAME_SETTING_BUFFERING

Control what kind of buffering is used, when using chunked image frames. -1 = default (let the encoder decide) 0 = buffers everything, basically the same as non-streamed code path (mainly for testing) 1 = buffers everything for images that are smaller than 2048 x 2048, and uses streaming input and output for larger images 2 = uses streaming input and output for all images that are larger than one group, i.e. 256 x 256 pixels by default 3 = currently same as 2

When using streaming input and output the encoder minimizes memory usage at the cost of compression density. Also note that images produced with streaming mode might not be progressively decodeable.

enumerator JXL_ENC_FRAME_SETTING_JPEG_KEEP_EXIF

Keep or discard Exif metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. When JxlEncoderStoreJPEGMetadata is set to 1, this option cannot be set to 0. Even when Exif metadata is discarded, the orientation will still be applied. 0 = discard Exif metadata, 1 = keep Exif metadata (default).

enumerator JXL_ENC_FRAME_SETTING_JPEG_KEEP_XMP

Keep or discard XMP metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. When JxlEncoderStoreJPEGMetadata is set to 1, this option cannot be set to 0. 0 = discard XMP metadata, 1 = keep XMP metadata (default).

enumerator JXL_ENC_FRAME_SETTING_JPEG_KEEP_JUMBF

Keep or discard JUMBF metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. 0 = discard JUMBF metadata, 1 = keep JUMBF metadata (default).

enumerator JXL_ENC_FRAME_SETTING_USE_FULL_IMAGE_HEURISTICS

If this mode is disabled, the encoder will not make any image quality decisions that are computed based on the full image, but stored only once (e.g. the X quant multiplier in the frame header). Used mainly for testing equivalence of streaming and non-streaming code. 0 = disabled, 1 = enabled (default)

enumerator JXL_ENC_FRAME_SETTING_FILL_ENUM

Enum value not to be used as an option. This value is added to force the C compiler to have the enum to take a known size.

enum JxlEncoderStatsKey

Data type for querying JxlEncoderStats object

Values:

enumerator JXL_ENC_STAT_HEADER_BITS
enumerator JXL_ENC_STAT_TOC_BITS
enumerator JXL_ENC_STAT_DICTIONARY_BITS
enumerator JXL_ENC_STAT_SPLINES_BITS
enumerator JXL_ENC_STAT_NOISE_BITS
enumerator JXL_ENC_STAT_QUANT_BITS
enumerator JXL_ENC_STAT_MODULAR_TREE_BITS
enumerator JXL_ENC_STAT_MODULAR_GLOBAL_BITS
enumerator JXL_ENC_STAT_DC_BITS
enumerator JXL_ENC_STAT_MODULAR_DC_GROUP_BITS
enumerator JXL_ENC_STAT_CONTROL_FIELDS_BITS
enumerator JXL_ENC_STAT_COEF_ORDER_BITS
enumerator JXL_ENC_STAT_AC_HISTOGRAM_BITS
enumerator JXL_ENC_STAT_AC_BITS
enumerator JXL_ENC_STAT_MODULAR_AC_GROUP_BITS
enumerator JXL_ENC_STAT_NUM_SMALL_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT4X8_BLOCKS
enumerator JXL_ENC_STAT_NUM_AFV_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT8_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT8X32_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT16_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT16X32_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT32_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT32X64_BLOCKS
enumerator JXL_ENC_STAT_NUM_DCT64_BLOCKS
enumerator JXL_ENC_STAT_NUM_BUTTERAUGLI_ITERS
enumerator JXL_ENC_NUM_STATS

Functions

JXL_EXPORT uint32_t JxlEncoderVersion(void)

Encoder library version.

Returns:

the encoder library version as an integer: MAJOR_VERSION * 1000000 + MINOR_VERSION * 1000 + PATCH_VERSION. For example, version 1.2.3 would return 1002003.

JXL_EXPORT JxlEncoder *JxlEncoderCreate(const JxlMemoryManager *memory_manager)

Creates an instance of JxlEncoder and initializes it.

memory_manager will be used for all the library dynamic allocations made from this instance. The parameter may be NULL, in which case the default allocator will be used. See jpegxl/memory_manager.h for details.

Parameters:

memory_manager – custom allocator function. It may be NULL. The memory manager will be copied internally.

Returns:

NULL if the instance can not be allocated or initialized

Returns:

pointer to initialized JxlEncoder otherwise

JXL_EXPORT void JxlEncoderReset(JxlEncoder *enc)

Re-initializes a JxlEncoder instance, so it can be re-used for encoding another image. All state and settings are reset as if the object was newly created with JxlEncoderCreate, but the memory manager is kept.

Parameters:

enc – instance to be re-initialized.

JXL_EXPORT void JxlEncoderDestroy(JxlEncoder *enc)

Deinitializes and frees a JxlEncoder instance.

Parameters:

enc – instance to be cleaned up and deallocated.

JXL_EXPORT void JxlEncoderSetCms(JxlEncoder *enc, JxlCmsInterface cms)

Sets the color management system (CMS) that will be used for color conversion (if applicable) during encoding. May only be set before starting encoding. If left unset, the default CMS implementation will be used.

Parameters:
  • enc – encoder object.

  • cms – structure representing a CMS implementation. See JxlCmsInterface for more details.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetParallelRunner(JxlEncoder *enc, JxlParallelRunner parallel_runner, void *parallel_runner_opaque)

Set the parallel runner for multithreading. May only be set before starting encoding.

Parameters:
  • enc – encoder object.

  • parallel_runner – function pointer to runner for multithreading. It may be NULL to use the default, single-threaded, runner. A multithreaded runner should be set to reach fast performance.

  • parallel_runner_opaque – opaque pointer for parallel_runner.

Returns:

JXL_ENC_SUCCESS if the runner was set, JXL_ENC_ERROR otherwise (the previous runner remains set).

JXL_EXPORT JxlEncoderError JxlEncoderGetError(JxlEncoder *enc)

Get the (last) error code in case JXL_ENC_ERROR was returned.

Parameters:

enc – encoder object.

Returns:

the JxlEncoderError that caused the (last) JXL_ENC_ERROR to be returned.

JXL_EXPORT JxlEncoderStatus JxlEncoderProcessOutput(JxlEncoder *enc, uint8_t **next_out, size_t *avail_out)

Encodes a JPEG XL file using the available bytes. *avail_out indicates how many output bytes are available, and *next_out points to the input bytes. *avail_out will be decremented by the amount of bytes that have been processed by the encoder and *next_out will be incremented by the same amount, so *next_out will now point at the amount of *avail_out unprocessed bytes.

The returned status indicates whether the encoder needs more output bytes. When the return value is not JXL_ENC_ERROR or JXL_ENC_SUCCESS, the encoding requires more JxlEncoderProcessOutput calls to continue.

The caller must guarantee that *avail_out >= 32 when calling JxlEncoderProcessOutput; otherwise, JXL_ENC_NEED_MORE_OUTPUT will be returned. It is guaranteed that, if *avail_out >= 32, at least one byte of output will be written.

This encodes the frames and/or boxes added so far. If the last frame or last box has been added, JxlEncoderCloseInput, JxlEncoderCloseFrames and/or JxlEncoderCloseBoxes must be called before the next JxlEncoderProcessOutput call, or the codestream won’t be encoded correctly.

Parameters:
  • enc – encoder object.

  • next_out – pointer to next bytes to write to.

  • avail_out – amount of bytes available starting from *next_out.

Returns:

JXL_ENC_SUCCESS when encoding finished and all events handled.

Returns:

JXL_ENC_ERROR when encoding failed, e.g. invalid input.

Returns:

JXL_ENC_NEED_MORE_OUTPUT more output buffer is necessary.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameHeader(JxlEncoderFrameSettings *frame_settings, const JxlFrameHeader *frame_header)

Sets the frame information for this frame to the encoder. This includes animation information such as frame duration to store in the frame header. The frame header fields represent the frame as passed to the encoder, but not necessarily the exact values as they will be encoded file format: the encoder could change crop and blending options of a frame for more efficient encoding or introduce additional internal frames. Animation duration and time code information is not altered since those are immutable metadata of the frame.

It is not required to use this function, however if have_animation is set to true in the basic info, then this function should be used to set the time duration of this individual frame. By default individual frames have a time duration of 0, making them form a composite still. See JxlFrameHeader for more information.

This information is stored in the JxlEncoderFrameSettings and so is used for any frame encoded with these JxlEncoderFrameSettings. It is ok to change between JxlEncoderAddImageFrame calls, each added image frame will have the frame header that was set in the options at the time of calling JxlEncoderAddImageFrame.

The is_last and name_length fields of the JxlFrameHeader are ignored, use JxlEncoderCloseFrames to indicate last frame, and JxlEncoderSetFrameName to indicate the name and its length instead. Calling this function will clear any name that was previously set with JxlEncoderSetFrameName.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • frame_header – frame header data to set. Object owned by the caller and does not need to be kept in memory, its information is copied internally.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelBlendInfo(JxlEncoderFrameSettings *frame_settings, size_t index, const JxlBlendInfo *blend_info)

Sets blend info of an extra channel. The blend info of extra channels is set separately from that of the color channels, the color channels are set with JxlEncoderSetFrameHeader.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • index – index of the extra channel to use.

  • blend_info – blend info to set for the extra channel

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameName(JxlEncoderFrameSettings *frame_settings, const char *frame_name)

Sets the name of the animation frame. This function is optional, frames are not required to have a name. This setting is a part of the frame header, and the same principles as for JxlEncoderSetFrameHeader apply. The name_length field of JxlFrameHeader is ignored by the encoder, this function determines the name length instead as the length in bytes of the C string.

The maximum possible name length is 1071 bytes (excluding terminating null character).

Calling JxlEncoderSetFrameHeader clears any name that was previously set.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • frame_name – name of the next frame to be encoded, as a UTF-8 encoded C string (zero terminated). Owned by the caller, and copied internally.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameBitDepth(JxlEncoderFrameSettings *frame_settings, const JxlBitDepth *bit_depth)

Sets the bit depth of the input buffer.

For float pixel formats, only the default JXL_BIT_DEPTH_FROM_PIXEL_FORMAT setting is allowed, while for unsigned pixel formats, JXL_BIT_DEPTH_FROM_CODESTREAM setting is also allowed. See the comment on JxlEncoderAddImageFrame for the effects of the bit depth setting.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • bit_depth – the bit depth setting of the pixel input

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderAddJPEGFrame(const JxlEncoderFrameSettings *frame_settings, const uint8_t *buffer, size_t size)

Sets the buffer to read JPEG encoded bytes from for the next frame to encode.

If JxlEncoderSetBasicInfo has not yet been called, calling JxlEncoderAddJPEGFrame will implicitly call it with the parameters of the added JPEG frame.

If JxlEncoderSetColorEncoding or JxlEncoderSetICCProfile has not yet been called, calling JxlEncoderAddJPEGFrame will implicitly call it with the parameters of the added JPEG frame.

If the encoder is set to store JPEG reconstruction metadata using JxlEncoderStoreJPEGMetadata and a single JPEG frame is added, it will be possible to losslessly reconstruct the JPEG codestream.

If this is the last frame, JxlEncoderCloseInput or JxlEncoderCloseFrames must be called before the next JxlEncoderProcessOutput call.

Note, this can only be used to add JPEG frames for lossless compression. To encode with lossy compression, the JPEG must be decoded manually and a pixel buffer added using JxlEncoderAddImageFrame.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • buffer – bytes to read JPEG from. Owned by the caller and its contents are copied internally.

  • size – size of buffer in bytes.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderAddImageFrame(const JxlEncoderFrameSettings *frame_settings, const JxlPixelFormat *pixel_format, const void *buffer, size_t size)

Sets the buffer to read pixels from for the next image to encode. Must call JxlEncoderSetBasicInfo before JxlEncoderAddImageFrame.

Currently only some data types for pixel formats are supported:

Note: the sample data type in pixel_format is allowed to be different from what is described in the JxlBasicInfo. The type in pixel_format, together with an optional JxlBitDepth parameter set by JxlEncoderSetFrameBitDepth describes the format of the uncompressed pixel buffer. The bits_per_sample and exponent_bits_per_sample in the JxlBasicInfo describes what will actually be encoded in the JPEG XL codestream. For example, to encode a 12-bit image, you would set bits_per_sample to 12, while the input frame buffer can be in the following formats:

We support interleaved channels as described by the JxlPixelFormat:

  • single-channel data, e.g. grayscale

  • single-channel + alpha

  • trichromatic, e.g. RGB

  • trichromatic + alpha

Extra channels not handled here need to be set by JxlEncoderSetExtraChannelBuffer. If the image has alpha, and alpha is not passed here, it will implicitly be set to all-opaque (an alpha value of 1.0 everywhere).

The pixels are assumed to be encoded in the original profile that is set with JxlEncoderSetColorEncoding or JxlEncoderSetICCProfile. If none of these functions were used, the pixels are assumed to be nonlinear sRGB for integer data types (JXL_TYPE_UINT8, JXL_TYPE_UINT16), and linear sRGB for floating point data types (JXL_TYPE_FLOAT16, JXL_TYPE_FLOAT).

Sample values in floating-point pixel formats are allowed to be outside the nominal range, e.g. to represent out-of-sRGB-gamut colors in the uses_original_profile=false case. They are however not allowed to be NaN or +-infinity.

If this is the last frame, JxlEncoderCloseInput or JxlEncoderCloseFrames must be called before the next JxlEncoderProcessOutput call.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • pixel_format – format for pixels. Object owned by the caller and its contents are copied internally.

  • buffer – buffer type to input the pixel data from. Owned by the caller and its contents are copied internally.

  • size – size of buffer in bytes. This size should match what is implied by the frame dimensions and the pixel format.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderSetOutputProcessor(JxlEncoder *enc, struct JxlEncoderOutputProcessor output_processor)

Sets the output processor for the encoder. This processor determines how the encoder will handle buffering, writing, seeking (if supported), and setting a finalized position during the encoding process.

This should not be used when using JxlEncoderProcessOutput.

Parameters:
  • enc – encoder object.

  • output_processor – the struct containing the callbacks for managing output.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error.

JXL_EXPORT JxlEncoderStatus JxlEncoderFlushInput(JxlEncoder *enc)

Flushes any buffered input in the encoder, ensuring that all available input data has been processed and written to the output.

This function can only be used after JxlEncoderSetOutputProcessor. Before making the last call to JxlEncoderFlushInput, users should call JxlEncoderCloseInput to signal the end of input data.

This should not be used when using JxlEncoderProcessOutput.

Parameters:

enc – encoder object.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error.

JXL_EXPORT JxlEncoderStatus JxlEncoderAddChunkedFrame(const JxlEncoderFrameSettings *frame_settings, JXL_BOOL is_last_frame, struct JxlChunkedFrameInputSource chunked_frame_input)

Adds a frame to the encoder using a chunked input source.

This function gives a way to encode a frame by providing pixel data in a chunked or streaming manner, which can be especially useful when dealing with large images that may not fit entirely in memory or when trying to optimize memory usage. The input data is provided through callbacks defined in the JxlChunkedFrameInputSource struct. Once the frame data has been completely retrieved, this function will flush the input and close it if it is the last frame.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • is_last_frame – indicates if this is the last frame.

  • chunked_frame_input – struct providing callback methods for retrieving pixel data in chunks.

Returns:

Returns a status indicating the success or failure of adding the frame.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelBuffer(const JxlEncoderFrameSettings *frame_settings, const JxlPixelFormat *pixel_format, const void *buffer, size_t size, uint32_t index)

Sets the buffer to read pixels from for an extra channel at a given index. The index must be smaller than the num_extra_channels in the associated JxlBasicInfo. Must call JxlEncoderSetExtraChannelInfo before JxlEncoderSetExtraChannelBuffer.

TODO(firsching): mention what data types in pixel formats are supported.

It is required to call this function for every extra channel, except for the alpha channel if that was already set through JxlEncoderAddImageFrame.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • pixel_format – format for pixels. Object owned by the caller and its contents are copied internally. The num_channels value is ignored, since the number of channels for an extra channel is always assumed to be one.

  • buffer – buffer type to input the pixel data from. Owned by the caller and its contents are copied internally.

  • size – size of buffer in bytes. This size should match what is implied by the frame dimensions and the pixel format.

  • index – index of the extra channel to use.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderAddBox(JxlEncoder *enc, const JxlBoxType type, const uint8_t *contents, size_t size, JXL_BOOL compress_box)

Adds a metadata box to the file format. JxlEncoderProcessOutput must be used to effectively write the box to the output. JxlEncoderUseBoxes must be enabled before using this function.

Boxes allow inserting application-specific data and metadata (Exif, XML/XMP, JUMBF and user defined boxes).

The box format follows ISO BMFF and shares features and box types with other image and video formats, including the Exif, XML and JUMBF boxes. The box format for JPEG XL is specified in ISO/IEC 18181-2.

Boxes in general don’t contain other boxes inside, except a JUMBF superbox. Boxes follow each other sequentially and are byte-aligned. If the container format is used, the JXL stream consists of concatenated boxes. It is also possible to use a direct codestream without boxes, but in that case metadata cannot be added.

Each box generally has the following byte structure in the file:

  • 4 bytes: box size including box header (Big endian. If set to 0, an 8-byte 64-bit size follows instead).

  • 4 bytes: type, e.g. “JXL “ for the signature box, “jxlc” for a codestream box.

  • N bytes: box contents.

Only the box contents are provided to the contents argument of this function, the encoder encodes the size header itself. Most boxes are written automatically by the encoder as needed (“JXL “, “ftyp”, “jxll”, “jxlc”, “jxlp”, “jxli”, “jbrd”), and this function only needs to be called to add optional metadata when encoding from pixels (using JxlEncoderAddImageFrame). When recompressing JPEG files (using JxlEncoderAddJPEGFrame), if the input JPEG contains EXIF, XMP or JUMBF metadata, the corresponding boxes are already added automatically.

Box types are given by 4 characters. The following boxes can be added with this function:

  • ”Exif”: a box with EXIF metadata, can be added by libjxl users, or is automatically added when needed for JPEG reconstruction. The contents of this box must be prepended by a 4-byte tiff header offset, which may be 4 zero bytes in case the tiff header follows immediately. The EXIF metadata must be in sync with what is encoded in the JPEG XL codestream, specifically the image orientation. While this is not recommended in practice, in case of conflicting metadata, the JPEG XL codestream takes precedence.

  • ”xml “: a box with XML data, in particular XMP metadata, can be added by libjxl users, or is automatically added when needed for JPEG reconstruction

  • ”jumb”: a JUMBF superbox, which can contain boxes with different types of metadata inside. This box type can be added by the encoder transparently, and other libraries to create and handle JUMBF content exist.

  • Application-specific boxes. Their typename should not begin with “jxl” or “JXL” or conflict with other existing typenames, and they should be registered with MP4RA (mp4ra.org).

These boxes can be stored uncompressed or Brotli-compressed (using a “brob” box), depending on the compress_box parameter.

Parameters:
  • enc – encoder object.

  • type – the box type, e.g. “Exif” for EXIF metadata, “xml “ for XMP or IPTC metadata, “jumb” for JUMBF metadata.

  • contents – the full contents of the box, for example EXIF data. ISO BMFF box header must not be included, only the contents. Owned by the caller and its contents are copied internally.

  • size – size of the box contents.

  • compress_box – Whether to compress this box as a “brob” box. Requires Brotli support.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error, such as when using this function without JxlEncoderUseContainer, or adding a box type that would result in an invalid file format.

JXL_EXPORT JxlEncoderStatus JxlEncoderUseBoxes(JxlEncoder *enc)

Indicates the intention to add metadata boxes. This allows JxlEncoderAddBox to be used. When using this function, then it is required to use JxlEncoderCloseBoxes at the end.

By default the encoder assumes no metadata boxes will be added.

This setting can only be set at the beginning, before encoding starts.

Parameters:

enc – encoder object.

JXL_EXPORT void JxlEncoderCloseBoxes(JxlEncoder *enc)

Declares that no further boxes will be added with JxlEncoderAddBox. This function must be called after the last box is added so the encoder knows the stream will be finished. It is not necessary to use this function if JxlEncoderUseBoxes is not used. Further frames may still be added.

Must be called between JxlEncoderAddBox of the last box and the next call to JxlEncoderProcessOutput, or JxlEncoderProcessOutput won’t output the last box correctly.

NOTE: if you don’t need to close frames and boxes at separate times, you can use JxlEncoderCloseInput instead to close both at once.

Parameters:

enc – encoder object.

JXL_EXPORT void JxlEncoderCloseFrames(JxlEncoder *enc)

Declares that no frames will be added and JxlEncoderAddImageFrame and JxlEncoderAddJPEGFrame won’t be called anymore. Further metadata boxes may still be added. This function or JxlEncoderCloseInput must be called after adding the last frame and the next call to JxlEncoderProcessOutput, or the frame won’t be properly marked as last.

NOTE: if you don’t need to close frames and boxes at separate times, you can use JxlEncoderCloseInput instead to close both at once.

Parameters:

enc – encoder object.

JXL_EXPORT void JxlEncoderCloseInput(JxlEncoder *enc)

Closes any input to the encoder, equivalent to calling JxlEncoderCloseFrames as well as calling JxlEncoderCloseBoxes if needed. No further input of any kind may be given to the encoder, but further JxlEncoderProcessOutput calls should be done to create the final output.

The requirements of both JxlEncoderCloseFrames and JxlEncoderCloseBoxes apply to this function. Either this function or the other two must be called after the final frame and/or box, and the next JxlEncoderProcessOutput call, or the codestream won’t be encoded correctly.

Parameters:

enc – encoder object.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetColorEncoding(JxlEncoder *enc, const JxlColorEncoding *color)

Sets the original color encoding of the image encoded by this encoder. This is an alternative to JxlEncoderSetICCProfile and only one of these two must be used. This one sets the color encoding as a JxlColorEncoding, while the other sets it as ICC binary data. Must be called after JxlEncoderSetBasicInfo.

Parameters:
  • enc – encoder object.

  • color – color encoding. Object owned by the caller and its contents are copied internally.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

JXL_EXPORT JxlEncoderStatus JxlEncoderSetICCProfile(JxlEncoder *enc, const uint8_t *icc_profile, size_t size)

Sets the original color encoding of the image encoded by this encoder as an ICC color profile. This is an alternative to JxlEncoderSetColorEncoding and only one of these two must be used. This one sets the color encoding as ICC binary data, while the other defines it as a JxlColorEncoding. Must be called after JxlEncoderSetBasicInfo.

Parameters:
  • enc – encoder object.

  • icc_profile – bytes of the original ICC profile

  • size – size of the icc_profile buffer in bytes

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

JXL_EXPORT void JxlEncoderInitBasicInfo(JxlBasicInfo *info)

Initializes a JxlBasicInfo struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields. The default values correspond to an 8-bit RGB image, no alpha or any other extra channels.

Parameters:

info – global image metadata. Object owned by the caller.

JXL_EXPORT void JxlEncoderInitFrameHeader(JxlFrameHeader *frame_header)

Initializes a JxlFrameHeader struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields. The default values correspond to a frame with no animation duration and the ‘replace’ blend mode. After using this function, For animation duration must be set, for composite still blend settings must be set.

Parameters:

frame_header – frame metadata. Object owned by the caller.

JXL_EXPORT void JxlEncoderInitBlendInfo(JxlBlendInfo *blend_info)

Initializes a JxlBlendInfo struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields.

Parameters:

blend_info – blending info. Object owned by the caller.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetBasicInfo(JxlEncoder *enc, const JxlBasicInfo *info)

Sets the global metadata of the image encoded by this encoder.

If the JxlBasicInfo contains information of extra channels beyond an alpha channel, then JxlEncoderSetExtraChannelInfo must be called between JxlEncoderSetBasicInfo and JxlEncoderAddImageFrame. In order to indicate extra channels, the value of info.num_extra_channels should be set to the number of extra channels, also counting the alpha channel if present.

Parameters:
  • enc – encoder object.

  • info – global image metadata. Object owned by the caller and its contents are copied internally.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

JXL_EXPORT JxlEncoderStatus JxlEncoderSetUpsamplingMode(JxlEncoder *enc, int64_t factor, int64_t mode)

Sets the upsampling method the decoder will use in case there are frames with JXL_ENC_FRAME_SETTING_RESAMPLING set. This is useful in combination with the JXL_ENC_FRAME_SETTING_ALREADY_DOWNSAMPLED option, to control the type of upsampling that will be used.

Parameters:
  • enc – encoder object.

  • factor – upsampling factor to configure (1, 2, 4 or 8; for 1 this function has no effect at all)

  • mode – upsampling mode to use for this upsampling: -1: default (good for photographic images, no signaling overhead) 0: nearest neighbor (good for pixel art) 1: ‘pixel dots’ (same as NN for 2x, diamond-shaped ‘pixel dots’ for 4x/8x)

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

JXL_EXPORT void JxlEncoderInitExtraChannelInfo(JxlExtraChannelType type, JxlExtraChannelInfo *info)

Initializes a JxlExtraChannelInfo struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields. The default values correspond to an 8-bit channel of the provided type.

Parameters:
  • type – type of the extra channel.

  • info – global extra channel metadata. Object owned by the caller and its contents are copied internally.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelInfo(JxlEncoder *enc, size_t index, const JxlExtraChannelInfo *info)

Sets information for the extra channel at the given index. The index must be smaller than num_extra_channels in the associated JxlBasicInfo.

Parameters:
  • enc – encoder object

  • index – index of the extra channel to set.

  • info – global extra channel metadata. Object owned by the caller and its contents are copied internally.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelName(JxlEncoder *enc, size_t index, const char *name, size_t size)

Sets the name for the extra channel at the given index in UTF-8. The index must be smaller than the num_extra_channels in the associated JxlBasicInfo.

TODO(lode): remove size parameter for consistency with JxlEncoderSetFrameName

Parameters:
  • enc – encoder object

  • index – index of the extra channel to set.

  • name – buffer with the name of the extra channel.

  • size – size of the name buffer in bytes, not counting the terminating character.

Returns:

JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

JXL_EXPORT JxlEncoderStatus JxlEncoderFrameSettingsSetOption(JxlEncoderFrameSettings *frame_settings, JxlEncoderFrameSettingId option, int64_t value)

Sets a frame-specific option of integer type to the encoder options. The JxlEncoderFrameSettingId argument determines which option is set.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • option – ID of the option to set.

  • value – Integer value to set for this option.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR in case of an error, such as invalid or unknown option id, or invalid integer value for the given option. If an error is returned, the state of the JxlEncoderFrameSettings object is still valid and is the same as before this function was called.

JXL_EXPORT JxlEncoderStatus JxlEncoderFrameSettingsSetFloatOption(JxlEncoderFrameSettings *frame_settings, JxlEncoderFrameSettingId option, float value)

Sets a frame-specific option of float type to the encoder options. The JxlEncoderFrameSettingId argument determines which option is set.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • option – ID of the option to set.

  • value – Float value to set for this option.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR in case of an error, such as invalid or unknown option id, or invalid integer value for the given option. If an error is returned, the state of the JxlEncoderFrameSettings object is still valid and is the same as before this function was called.

JXL_EXPORT JxlEncoderStatus JxlEncoderUseContainer(JxlEncoder *enc, JXL_BOOL use_container)

Forces the encoder to use the box-based container format (BMFF) even when not necessary.

When using JxlEncoderUseBoxes, JxlEncoderStoreJPEGMetadata or JxlEncoderSetCodestreamLevel with level 10, the encoder will automatically also use the container format, it is not necessary to use JxlEncoderUseContainer for those use cases.

By default this setting is disabled.

This setting can only be set at the beginning, before encoding starts.

Parameters:
  • enc – encoder object.

  • use_container – true if the encoder should always output the JPEG XL container format, false to only output it when necessary.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

JXL_EXPORT JxlEncoderStatus JxlEncoderStoreJPEGMetadata(JxlEncoder *enc, JXL_BOOL store_jpeg_metadata)

Configure the encoder to store JPEG reconstruction metadata in the JPEG XL container.

If this is set to true and a single JPEG frame is added, it will be possible to losslessly reconstruct the JPEG codestream.

This setting can only be set at the beginning, before encoding starts.

Parameters:
  • enc – encoder object.

  • store_jpeg_metadata – true if the encoder should store JPEG metadata.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetCodestreamLevel(JxlEncoder *enc, int level)

Sets the feature level of the JPEG XL codestream. Valid values are 5 and 10, or -1 (to choose automatically). Using the minimum required level, or level 5 in most cases, is recommended for compatibility with all decoders.

Level 5: for end-user image delivery, this level is the most widely supported level by image decoders and the recommended level to use unless a level 10 feature is absolutely necessary. Supports a maximum resolution 268435456 pixels total with a maximum width or height of 262144 pixels, maximum 16-bit color channel depth, maximum 120 frames per second for animation, maximum ICC color profile size of 4 MiB, it allows all color models and extra channel types except CMYK and the JXL_CHANNEL_BLACK extra channel, and a maximum of 4 extra channels in addition to the 3 color channels. It also sets boundaries to certain internally used coding tools.

Level 10: this level removes or increases the bounds of most of the level 5 limitations, allows CMYK color and up to 32 bits per color channel, but may be less widely supported.

The default value is -1. This means the encoder will automatically choose between level 5 and level 10 based on what information is inside the JxlBasicInfo structure. Do note that some level 10 features, particularly those used by animated JPEG XL codestreams, might require level 10, even though the JxlBasicInfo only suggests level 5. In this case, the level must be explicitly set to 10, otherwise the encoder will return an error. The encoder will restrict internal encoding choices to those compatible with the level setting.

This setting can only be set at the beginning, before encoding starts.

Parameters:
  • enc – encoder object.

  • level – the level value to set, must be -1, 5, or 10.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

JXL_EXPORT int JxlEncoderGetRequiredCodestreamLevel(const JxlEncoder *enc)

Returns the codestream level required to support the currently configured settings and basic info. This function can only be used at the beginning, before encoding starts, but after setting basic info.

This does not support per-frame settings, only global configuration, such as the image dimensions, that are known at the time of writing the header of the JPEG XL file.

If this returns 5, nothing needs to be done and the codestream can be compatible with any decoder. If this returns 10, JxlEncoderSetCodestreamLevel has to be used to set the codestream level to 10, or the encoder can be configured differently to allow using the more compatible level 5.

Parameters:

enc – encoder object.

Returns:

-1 if no level can support the configuration (e.g. image dimensions larger than even level 10 supports), 5 if level 5 is supported, 10 if setting the codestream level to 10 is required.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameLossless(JxlEncoderFrameSettings *frame_settings, JXL_BOOL lossless)

Enables lossless encoding.

This is not an option like the others on itself, but rather while enabled it overrides a set of existing options (such as distance, modular mode and color transform) that enables bit-for-bit lossless encoding.

When disabled, those options are not overridden, but since those options could still have been manually set to a combination that operates losslessly, using this function with lossless set to JXL_FALSE does not guarantee lossy encoding, though the default set of options is lossy.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • lossless – whether to override options for lossless mode

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameDistance(JxlEncoderFrameSettings *frame_settings, float distance)

Sets the distance level for lossy compression: target max butteraugli distance, lower = higher quality. Range: 0 .. 25. 0.0 = mathematically lossless (however, use JxlEncoderSetFrameLossless instead to use true lossless, as setting distance to 0 alone is not the only requirement). 1.0 = visually lossless. Recommended range: 0.5 .. 3.0. Default value: 1.0.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • distance – the distance value to set.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelDistance(JxlEncoderFrameSettings *frame_settings, size_t index, float distance)

Sets the distance level for lossy compression of extra channels. The distance is as in JxlEncoderSetFrameDistance (lower = higher quality). If not set, or if set to the special value -1, the distance that was set with JxlEncoderSetFrameDistance will be used.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • index – index of the extra channel to set a distance value for.

  • distance – the distance value to set.

Returns:

JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

JXL_EXPORT float JxlEncoderDistanceFromQuality(float quality)

Maps JPEG-style quality factor to distance.

This function takes in input a JPEG-style quality factor quality and produces as output a distance value suitable to be used with JxlEncoderSetFrameDistance and JxlEncoderSetExtraChannelDistance.

The distance value influences the level of compression, with lower values indicating higher quality:

  • 0.0 implies lossless compression (however, note that calling JxlEncoderSetFrameLossless is required).

  • 1.0 represents a visually lossy compression, which is also the default setting.

The quality parameter, ranging up to 100, is inversely related to ‘distance’:

  • A quality of 100.0 maps to a distance of 0.0 (lossless).

  • A quality of 90.0 corresponds to a distance of 1.0.

Recommended Range:

  • distance: 0.5 to 3.0.

  • corresponding quality: approximately 96 to 68.

Allowed Range:

  • distance: 0.0 to 25.0.

  • corresponding quality: 100.0 to 0.0.

Note: the quality parameter has no consistent psychovisual meaning across different codecs and libraries. Using the mapping defined by JxlEncoderDistanceFromQuality will result in a visual quality roughly equivalent to what would be obtained with libjpeg-turbo with the same quality parameter, but that is by no means guaranteed; do not assume that the same quality value will result in similar file sizes and image quality across different codecs.

JXL_EXPORT JxlEncoderFrameSettings *JxlEncoderFrameSettingsCreate(JxlEncoder *enc, const JxlEncoderFrameSettings *source)

Create a new set of encoder options, with all values initially copied from the source options, or set to default if source is NULL.

The returned pointer is an opaque struct tied to the encoder and it will be deallocated by the encoder when JxlEncoderDestroy() is called. For functions taking both a JxlEncoder and a JxlEncoderFrameSettings, only JxlEncoderFrameSettings created with this function for the same encoder instance can be used.

Parameters:
  • enc – encoder object.

  • source – source options to copy initial values from, or NULL to get defaults initialized to defaults.

Returns:

the opaque struct pointer identifying a new set of encoder options.

JXL_EXPORT void JxlColorEncodingSetToSRGB(JxlColorEncoding *color_encoding, JXL_BOOL is_gray)

Sets a color encoding to be sRGB.

Parameters:
  • color_encoding – color encoding instance.

  • is_gray – whether the color encoding should be gray scale or color.

JXL_EXPORT void JxlColorEncodingSetToLinearSRGB(JxlColorEncoding *color_encoding, JXL_BOOL is_gray)

Sets a color encoding to be linear sRGB.

Parameters:
  • color_encoding – color encoding instance.

  • is_gray – whether the color encoding should be gray scale or color.

JXL_EXPORT void JxlEncoderAllowExpertOptions(JxlEncoder *enc)

Enables usage of expert options.

At the moment, the only expert option is setting an effort value of 11, which gives the best compression for pixel-lossless modes but is very slow.

Parameters:

enc – encoder object.

JXL_EXPORT void JxlEncoderSetDebugImageCallback(JxlEncoderFrameSettings *frame_settings, JxlDebugImageCallback callback, void *opaque)

Sets the given debug image callback that will be used by the encoder to output various debug images during encoding.

This only has any effect if the encoder was compiled with the appropriate debug build flags.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • callback – used to return the debug image

  • opaque – user supplied parameter to the image callback

JXL_EXPORT void JxlEncoderCollectStats(JxlEncoderFrameSettings *frame_settings, JxlEncoderStats *stats)

Sets the given stats object for gathering various statistics during encoding.

This only has any effect if the encoder was compiled with the appropriate debug build flags.

Parameters:
  • frame_settings – set of options and metadata for this frame. Also includes reference to the encoder object.

  • stats – object that can be used to query the gathered stats (created by JxlEncoderStatsCreate)

JXL_EXPORT JxlEncoderStats *JxlEncoderStatsCreate(void)

Creates an instance of JxlEncoderStats and initializes it.

Returns:

pointer to initialized JxlEncoderStats instance

JXL_EXPORT void JxlEncoderStatsDestroy(JxlEncoderStats *stats)

Deinitializes and frees JxlEncoderStats instance.

Parameters:

stats – instance to be cleaned up and deallocated. No-op if stats is null pointer.

JXL_EXPORT size_t JxlEncoderStatsGet(const JxlEncoderStats *stats, JxlEncoderStatsKey key)

Returns the value of the statistics corresponding the given key.

Parameters:
  • stats – object that was passed to the encoder with a JxlEncoderCollectStats function

  • key – the particular statistics to query

Returns:

the value of the statistics

JXL_EXPORT void JxlEncoderStatsMerge(JxlEncoderStats *stats, const JxlEncoderStats *other)

Updates the values of the given stats object with that of an other.

Parameters:
  • stats – object whose values will be updated (usually added together)

  • other – stats object whose values will be merged with stats

struct JxlEncoderOutputProcessor
#include <encode.h>

The JxlEncoderOutputProcessor structure provides an interface for the encoder’s output processing. Users of the library, who want to do streaming encoding, should implement the required callbacks for buffering, writing, seeking (if supported), and setting a finalized position during the encoding process.

At a high level, the processor can be in one of two states:

  • With an active buffer: This indicates that a buffer has been acquired using get_buffer and encoded data can be written to it.

  • Without an active buffer: In this state, no data can be written. A new buffer must be acquired after releasing any previously active buffer.

The library will not acquire more than one buffer at a given time.

The state of the processor includes position and finalized position, which have the following meaning.

  • position: Represents the current position, in bytes, within the output stream where the encoded data will be written next. This position moves forward with each release_buffer call as data is written, and can also be adjusted through the optional seek callback, if provided. At this position the next write will occur.

  • finalized position: A position in the output stream that ensures all bytes before this point are finalized and won’t be changed by later writes.

All fields but seek are required, seek is optional and can be NULL.

Public Members

void *opaque

Required. An opaque pointer that the client can use to store custom data. This data will be passed to the associated callback functions.

void *(*get_buffer)(void *opaque, size_t *size)

Required. Acquires a buffer at the current position into which the library will write the output data.

If the size argument points to 0 and the returned value is NULL, this will be interpreted as asking the output writing to stop. In such a case, the library will return an error. The client is expected to set the size of the returned buffer based on the suggested size when this function is called.

Param opaque:

user supplied parameters to the callback

Param size:

points to a suggested buffer size when called; must be set to the size of the returned buffer once the function returns.

Return:

a pointer to the acquired buffer or NULL to indicate a stop condition.

void (*release_buffer)(void *opaque, size_t written_bytes)

Required. Notifies the user of library that the current buffer’s data has been written and can be released. This function should advance the current position of the buffer by written_bytes number of bytes.

Param opaque:

user supplied parameters to the callback

Param written_bytes:

the number of bytes written to the buffer.

void (*seek)(void *opaque, uint64_t position)

Optional, can be NULL Seeks to a specific position in the output. This function is optional and can be set to NULL if the output doesn’t support seeking. Can only be done when there is no buffer. Cannot be used to seek before the finalized position.

Param opaque:

user supplied parameters to the callback

Param position:

the position to seek to, in bytes.

void (*set_finalized_position)(void *opaque, uint64_t finalized_position)

Required. Sets a finalized position on the output data, at a specific position. Seeking will never request a position before the finalized position.

Will only be called if there is no active buffer.

Param opaque:

user supplied parameters to the callback

Param finalized_position:

the position, in bytes, where the finalized position should be set.

struct JxlChunkedFrameInputSource
#include <encode.h>

This struct provides callback functions to pass pixel data in a streaming manner instead of requiring the entire frame data in memory at once.

Public Members

void *opaque

A pointer to any user-defined data or state. This can be used to pass information to the callback functions.

void (*get_color_channels_pixel_format)(void *opaque, JxlPixelFormat *pixel_format)

Get the pixel format that color channel data will be provided in. When called, pixel_format points to a suggested pixel format; if color channel data can be given in this pixel format, processing might be more efficient.

This function will be called exactly once, before any call to get_color_channel_at.

Param opaque:

user supplied parameters to the callback

Param pixel_format:

format for pixels

const void *(*get_color_channel_data_at)(void *opaque, size_t xpos, size_t ypos, size_t xsize, size_t ysize, size_t *row_offset)

Callback to retrieve a rectangle of color channel data at a specific location. It is guaranteed that xpos and ypos are multiples of 8. xsize, ysize will be multiples of 8, unless the resulting rectangle would be out of image bounds. Moreover, xsize and ysize will be at most 2048. The returned data will be assumed to be in the format returned by the (preceding) call to get_color_channels_pixel_format, except the align parameter of the pixel format will be ignored. Instead, the i-th row will be assumed to start at position return_value + i * *row_offset, with the value of *row_offset decided by the callee.

Note that multiple calls to get_color_channel_data_at may happen before a call to release_buffer.

Param opaque:

user supplied parameters to the callback

Param xpos:

horizontal position for the data.

Param ypos:

vertical position for the data.

Param xsize:

horizontal size of the requested rectangle of data.

Param ysize:

vertical size of the requested rectangle of data.

Param row_offset:

pointer to a the byte offset between consecutive rows of the retrieved pixel data.

Return:

pointer to the retrieved pixel data.

void (*get_extra_channel_pixel_format)(void *opaque, size_t ec_index, JxlPixelFormat *pixel_format)

Get the pixel format that extra channel data will be provided in. When called, pixel_format points to a suggested pixel format; if extra channel data can be given in this pixel format, processing might be more efficient.

This function will be called exactly once per index, before any call to get_extra_channel_data_at with that given index.

Param opaque:

user supplied parameters to the callback

Param ec_index:

zero-indexed index of the extra channel

Param pixel_format:

format for extra channel data

const void *(*get_extra_channel_data_at)(void *opaque, size_t ec_index, size_t xpos, size_t ypos, size_t xsize, size_t ysize, size_t *row_offset)

Callback to retrieve a rectangle of extra channel ec_index data at a specific location. It is guaranteed that xpos and ypos are multiples of

  1. xsize, ysize will be multiples of 8, unless the resulting rectangle would be out of image bounds. Moreover, xsize and ysize will be at most

  2. The returned data will be assumed to be in the format returned by the (preceding) call to get_extra_channels_pixel_format_at with the corresponding extra channel index ec_index, except the align parameter of the pixel format will be ignored. Instead, the i-th row will be assumed to start at position return_value + i * *row_offset, with the value of *row_offset decided by the callee.

Note that multiple calls to get_extra_channel_data_at may happen before a call to release_buffer.

Param opaque:

user supplied parameters to the callback

Param xpos:

horizontal position for the data.

Param ypos:

vertical position for the data.

Param xsize:

horizontal size of the requested rectangle of data.

Param ysize:

vertical size of the requested rectangle of data.

Param row_offset:

pointer to a the byte offset between consecutive rows of the retrieved pixel data.

Return:

pointer to the retrieved pixel data.

void (*release_buffer)(void *opaque, const void *buf)

Releases the buffer buf (obtained through a call to get_color_channel_data_at or get_extra_channel_data_at). This function will be called exactly once per call to get_color_channel_data_at or get_extra_channel_data_at.

Param opaque:

user supplied parameters to the callback

Param buf:

pointer returned by get_color_channel_data_at or get_extra_channel_data_at