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Add JPEG‑XL Support to libcupsfilters (WoC 4.0 Contribution) #82

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TitikshaBansal
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Add JPEG‑XL Support to libcupsfilters

This pull request adds initial support for the JPEG‑XL image format to libcupsfilters. With these changes, cups‑filters can now detect, decode, and convert JPEG‑XL files into PDF and raster formats, thereby enabling printing via CUPS.

Note: This pull request does not include modifications for MIME type definitions; those changes will be submitted in a separate pull request.

Overview

JPEG‑XL Detection

  • Function Updated: is_jpegxl() in image-jpeg-xl.c. Checks for both standard JPEG‑XL signature (\x00\x00\x00\x0C\x4A\x58\x4C\x20) and the JPEG‑XL stream signature (\xFF\x0A).

Decoding Implementation

  • New Functions:
    • _cfImageReadJPEGXL()
    • _cfImageOpenJPEGXL()
  • Core Decoder Function:
    • cf_image_create_from_jxl_decoder()
      • Sets up a JxlPixelFormat requesting 16‑bit per channel output.
      • Processes the decoder input until the full image is decoded.
      • Detailed logging has been added via fprintf(stderr, ...) to log file size, status codes, and key variable values for debugging.

Build System Updates

  • Linking: The build configuration now uses pkg-config to link against libjxl.
  • Integration: The JPEG‑XL code integrates with existing filters for PDF and raster conversion.

Testing and Verification

  • Decoder Verification: The JPEG‑XL support was verified using the djxl tool and by testing conversions through cups‑filters.
  • Output Validation: Output PDF and raster files were inspected using utilities like rasterview to ensure correct color depth and page dimensions.
  • Debug Logging: Added extensive logging in the JPEG‑XL functions to assist in diagnosing any issues.

Future Work

  • Error Handling: Enhance error handling and add more comprehensive unit tests.
  • Optimizations: Further optimize performance and extend support for additional JPEG‑XL profiles.
  • MIME Type Integration: Develop and submit a separate PR for updating MIME type definitions for JPEG‑XL.

Background

This contribution was developed as part of the WoC 4.0 event organized by IIIT Kalyani. I have enjoyed working on integrating JPEG‑XL support into cups‑filters and am eager to continue contributing to this project even after the event concludes.

GitHub Repository: https://github.com/TitikshaBansal/libcupsfilters
Branch: features/jpegxl-support

Thank you for reviewing my contribution. I look forward to your feedback and further improvements.

Best regards,
Titiksha Bansal

@TitikshaBansal
Update configure.ac for the input support
17427de
@TitikshaBansal
Update imagetopdf.c
6f94361
@TitikshaBansal
Updated imagetoraster.c for jpegxl input support
ab9c8e5
@TitikshaBansal
added jxl decoder
1976507
@TitikshaBansal
Update imagetoraster.c
f51bea4
@TitikshaBansal
Update imagetopdf.c
8a6147b
@TitikshaBansal
Updated image-private.h
a1c94c5 
Added an inclusion of your new header for JPEG‑XL support.
@TitikshaBansal
Update image.c
eae7881 
In the block that checks the header for PNG, JPEG, and TIFF, added a new branch for JPEG‑XL.
We add an #ifdef HAVE_LIBJXL branch that calls _cfImageReadJPEGXL() if is_jpegxl() returns true.
Now, whether the user is converting to PDF (via imagetopdf.c) or to Raster (via imagetoraster.c), they call cfImageOpen() (and thus cfImageOpenFP()) which now supports JPEG‑XL.
@TitikshaBansal
Create image-jpeg-xl.h
34ee8de 
Created a header file for your JPEG‑XL functions.
@TitikshaBansal
Create image-jpeg-xl.c
e540afb 
Implemented the JPEG‑XL–specific functions.
In this the extra parameters (primary, secondary, saturation, hue, lut) are passed but not used because the JPEG‑XL decoder (via libjxl) handles the uncompression and preserves full quality.
@TitikshaBansal
Update image-jpeg-xl.c
863e453 
Implementation for cfImageCreateFromJxlDecoder(). 
This function uses the libjxl API to extract the frame header, compute the required output buffer size (requesting 16‑bit output for full quality), allocate memory for the decoded pixels, and then fill in a cf_image_t structure with the image properties.
@TitikshaBansal
Update imagetopdf.c
f88fb14 
Reverted the changes made earlier in the file.
@TitikshaBansal
Update imagetoraster.c
d950436 
Reverted all the changes made earlier.
@TitikshaBansal
Update image-jpeg-xl.h
a642841
@TitikshaBansal
Update image-jpeg-xl.c
848a6d0
@TitikshaBansal
Update Makefile.am
55694dd
@TitikshaBansal
Update image-jpeg-xl.h
9ee3a7e 
Updated file to handle the errors encountered while make.
@TitikshaBansal
Update image-jpeg-xl.c
f695114 
Made changes to handle errors during make
@TitikshaBansal
Update image.c
f83a11a 
Updated file to handle errors encountered while make
@TitikshaBansal
Update image.c
a32702b
@TitikshaBansal
Update Makefile.am
9ef007d
@TitikshaBansal
Update image-jpeg-xl.c
0482e95
@TitikshaBansal
Update image-jpeg-xl.c
d305203
@TitikshaBansal
Update image.c
a5abe34
@TitikshaBansal
Update image-jpeg-xl.c
8c5160b
@TitikshaBansal
Update image.c
172aad1
@TitikshaBansal
Update image-jpeg-xl.c
4a3b03f
@TitikshaBansal
Update image-jpeg-xl.c
d7f1e71
@TitikshaBansal
Update Makefile.am
a37da88
@TitikshaBansal
Update Makefile.am
d4fc1c8
@tillkamppeter
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What is now missing is:

  • Please check each function whether
    • it is used only in the file where it is defined/implemented: In this case declare it static and give to it an underscore-separated lowercase name. Do not declare such functions in any of the *.h files.
    • it is used only inside libcupsfilters but also in other files than the one where it got defined/implemented: Do not declare it static, name it in camelCase, starting with _cf, and declare it in a private *.h file (image-*.h, *-private.h).
    • Your work should not contain any new function for the public API, so do not name any of your functions in camelCase starting with cf.
  • Please make sure not to change the whitespace in any file which existed before your PR.

Please always test-build after each code change!!

tillkamppeter
tillkamppeter reviewed Mar 5, 2025
View reviewed changes
cupsfilters/image.c Outdated
@@ -71,7 +78,7 @@ cfImageClose(cf_image_t *img) // I - Image to close
close(img->cachefile);
unlink(img->cachename);
}

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Please make sure not having any whitespace-only changes.

@tillkamppeter
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Thank you very much!

  • Function naming and comments are correct now.
  • image.c still contains many whitespace-only changes. Especially take care not adding whitespace at the end of a line.
  • Please add copyright/license/contents header comments to the files you have added, as other files, like image-jpeg.c have.
  • Check you CI testing, especially which packages get installed for the CI testing. Yesterday I have seen that the CI test had failed as the code did not build due to lack of libjxl.

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@TitikshaBansal @tillkamppeter