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

TitikshaBansal · 2025-03-04T17:38:06Z

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

Added an inclusion of your new header for JPEG‑XL support.

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.

Created a header file for your JPEG‑XL functions.

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.

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.

Reverted the changes made earlier in the file.

Reverted all the changes made earlier.

Updated file to handle the errors encountered while make.

Made changes to handle errors during make

Updated file to handle errors encountered while make

Makefile.am

cupsfilters/image-jpeg-xl.c

cupsfilters/image.c

tillkamppeter · 2025-03-04T18:28:47Z

Also do not use fprintf(stderr, ...). Please use the log function instead. See the other cupsfilters/image*.c files.

tillkamppeter · 2025-03-04T19:26:59Z

cupsfilters/image-jpeg-xl.c

@@ -28,12 +27,14 @@ is_jpegxl(const unsigned char *header, size_t len)
 }

 /*
- * cf_image_create_from_jxl_decoder() - Create a cf_image_t from a libjxl decoder.
+ * cfImageCreateFromJxlDecoder() - Create a cf_image_t from a libjxl decoder.


Why are you changing the name in the comment?

The scheme for the name, underscore-separated lowercase is correct, as the function is static.

tillkamppeter · 2025-03-04T21:39:39Z

cupsfilters/image.c

@@ -38,12 +38,17 @@


 #include "image-private.h"
+
+


Now we have too many 2-line spacings. Do only 2-line spacings

Between the implementations of 2 functions

Once between header comment and first #include, between #includes and macro definitions, between macro definitions and data types, between data types and functions

Do not do 2-line spacings withing functions or withing data types

Especially do not change the wihitespace in files which were already there before your PR.

tillkamppeter · 2025-03-04T21:48:47Z

cupsfilters/image-jpeg-xl.c


-  // Process input until full image is decoded.
+  /* Process input until full image is decoded. */


For comments please use // ... and not /* ... */ to align with the other files of libcupsfilters (and with OpenPrinting's code style).

tillkamppeter · 2025-03-04T21:54:53Z

Please check the file DEVELOPING.md for information about coding style. Especially do the naming of functions as follows:

### Functions

Functions with a global scope have a lowercase prefix followed by capitalized
words, e.g., `cfDoThis`, `cfDoThat`, `cfDoSomethingElse`, etc.  Private
global functions begin with a leading underscore, e.g., `_cfDoThis`,
`_cfDoThat`, etc.

Functions with a local scope are declared static with lowercase names and
underscores between words, e.g., `do_this`, `do_that`, `do_something_else`, etc.

In short:

Public API of libcupsfilters: cfDoThis()
libcupsfilters-internal function used in more than one file: _cfDoThat()
static function (only used in the same file): do_something_else()

tillkamppeter · 2025-03-04T22:01:44Z

Makefile.am

@@ -1,4 +1,6 @@
 ACLOCAL_AMFLAGS = -I m4
+AM_CPPFLAGS = $(shell pkg-config --cflags libjxl)
+



Please remove this. All needed variables are set in configure.ac. Do not call pkg-config in Makefile.am.

tillkamppeter · 2025-03-04T22:06:02Z

cupsfilters/image-jpeg-xl.c

+ * JPEG‑XL stream signature.
+ */
+static int
+_cf_is_jpegxl(const unsigned char *header, size_t len)


This function is used in the file image.c, therefore do not declare it as static and also name it to _cfIsJPEGXL().

Please always test-build when doing any code changes!

tillkamppeter · 2025-03-04T22:19:22Z

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!!

TitikshaBansal added 30 commits February 17, 2025 00:34

Update configure.ac for the input support

17427de

Update imagetopdf.c

6f94361

Updated imagetoraster.c for jpegxl input support

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added jxl decoder

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Update imagetoraster.c

f51bea4

Update imagetopdf.c

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Updated image-private.h

a1c94c5

Added an inclusion of your new header for JPEG‑XL support.

Create image-jpeg-xl.h

34ee8de

Created a header file for your JPEG‑XL functions.

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.

Update imagetopdf.c

f88fb14

Reverted the changes made earlier in the file.

Update imagetoraster.c

d950436

Reverted all the changes made earlier.

Update image-jpeg-xl.h

a642841

Update image-jpeg-xl.c

848a6d0

Update Makefile.am

55694dd

Update image-jpeg-xl.h

9ee3a7e

Updated file to handle the errors encountered while make.

Update image-jpeg-xl.c

f695114

Made changes to handle errors during make

Update image.c

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Updated file to handle errors encountered while make

Update image.c

a32702b

Update Makefile.am

9ef007d

Update image-jpeg-xl.c

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Update image-jpeg-xl.c

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Update image.c

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Update image-jpeg-xl.c

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Update image.c

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Update Makefile.am

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TitikshaBansal added 7 commits March 3, 2025 23:33

Update Makefile.am

6a57f5b

Update image-jpeg-xl.c

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Update Makefile.am

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TitikshaBansal added 2 commits March 5, 2025 00:44

Update Makefile.am

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

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

TitikshaBansal commented Mar 4, 2025

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tillkamppeter commented Mar 4, 2025


		// Process input until full image is decoded.
		/* Process input until full image is decoded. */

		@@ -1,4 +1,6 @@
		ACLOCAL_AMFLAGS = -I m4
		AM_CPPFLAGS = $(shell pkg-config --cflags libjxl)

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

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

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TitikshaBansal commented Mar 4, 2025

Add JPEG‑XL Support to libcupsfilters

Overview

JPEG‑XL Detection

Decoding Implementation

Build System Updates

Testing and Verification

Future Work

Background

tillkamppeter commented Mar 4, 2025

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