NAME¶
djxl - decompress JPEG XL images
SYNOPSIS¶
djxl [options...] input.jxl
[output]
DESCRIPTION¶
djxl decompresses a JPEG XL image or animation. The output format
is determined by the extension of the output file, which can be .png, .jpg,
.ppm, .pfm. If the JPEG XL input file contains an animation, multiple output
files will be produced, with names of the form
"output-framenumber.ext".
OPTIONS¶
-V, --version
Print version number and exit
--num_reps=N
Sets the number of times to decompress the image. Used
for benchmarking, the default is 1.
--num_threads=N
Sets the number of threads to use. The default 0 value
means the machine default.
--bits_per_sample=N
Sets the output bit depth. The default 0 value means the
original (input) bit depth.
--display_nits=0.3-250
If set to a non-zero value, tone maps the image the given
peak display luminance.
--color_space=RGB_D65_SRG_Rel_Lin
Defaults to original (input) color space
-s N, --downsampling=N
If set and the input JXL stream is progressive and
contains hints for target downsampling ratios, the decoder will skip any
progressive passes that are not needed to produce a partially decoded image
intended for this downsampling ratio.
--allow_partial_files
Allow decoding of truncated files.
-j, --pixels_to_jpeg
By default, if the input JPEG XL contains a recompressed
JPEG file, djxl reconstructs the exact original JPEG file. This flag causes
the decoder to instead decode the image to pixels and encode a new (lossy)
JPEG. The output file if provided must be a .jpg or .jpeg file.
-q N, --jpeg_quality=N
Sets the JPEG output quality, default is 95. Setting an
output quality implies --pixels_to_jpeg.
--norender_spotcolors Disables rendering spot colors.
--preview_out=FILENAME
If specified, writes the preview image to this
file.
--icc_out=FILENAME
If specified, writes the ICC profile of the decoded image
to this file.
--orig_icc_out=FILENAME
If specified, writes the ICC profile of the original
image to this file. This can be different from the ICC profile of the decoded
image if --color_space was specified, or if the image was XYB encoded and the
color conversion to the original profile was not supported by the
decoder.
--metadata_out=FILENAME
If specified, writes decoded metadata info to this file
in JSON format. Used by the conformance test script
--print_read_bytes
Print total number of decoded bytes.
--quiet
Silence output (except for errors).
-h, --help
Displays the options that djxl supports.
EXAMPLES¶
# Decompress a JPEG XL file to PNG
$ djxl input.jxl output.png
# Reconstruct a losslessly-recompressed JPEG file
$ djxl lossless-jpeg.jxl reconstructed.jpeg
# Lossless compression
Lossless pixel compression only preserves the pixels losslessly,
not the input bitstream. To check that the pixels are identical, one can do
something like the following (if this says 0, then the maximum pixel error
is 0, so it’s lossless):
# Lossless compression of PNG:
$ cjxl -d 0.0 input.png lossless.png
# Decompress a JPEG XL file to PNG
$ djxl lossless.jxl lossless.png
$ compare -metric pae input.png lossless.png null:
0 (0)
