added CMYK/YCCK support for JPGs

[chruffins]

Addresses #1720 by adding color space conversion for CMYK/YCCK. Also, add automatic color space conversion for other color spaces through libjpeg. Added a CMYK conversion of the Alex logo for testing.

Summary by CodeRabbit

• Bug Fixes
  • Improved JPEG color-space handling to correctly detect and convert CMYK and YCCK images to RGB, preserving accurate colors.
  • Expanded component validation to accept 3- and 4-component JPEGs for broader file compatibility.
  • Enhanced multi-component JPEG processing for more consistent image loading and color accuracy.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📝 Walkthrough

Walkthrough

Adds CMYK handling to JPEG decompression: after reading the JPEG header the code detects color space, sets output to CMYK for CMYK/YCCK or RGB otherwise, accepts 3 or 4 components, and implements a 4-component CMYK->RGB per-pixel conversion while keeping the existing 3-component RGB path.

Changes

Cohort / File(s)	Summary
JPEG CMYK support addons/image/jpg.c	Detect color space after header read; accept 3 or 4 components; add a dedicated 4-component path that reads 4 bytes/pixel and converts inverted libjpeg CMYK to 3-byte RGB per pixel; retain existing 3-component RGB scanline handling.

Sequence Diagram(s)

sequenceDiagram
    participant JPEG_Header as JPEG Header Reader
    participant Decompress as Decompressor
    participant Bitmap as Destination Bitmap

    JPEG_Header->>Decompress: read_header()
    Decompress->>Decompress: detect_color_space (RGB / CMYK/YCCK)
    alt CMYK (4 components)
        Decompress->>Decompress: allocate 4-byte row buffer
        Decompress->>Decompress: read_scanline_4c()
        Decompress->>Decompress: convert_CMYK_to_RGB_per_pixel()
        Decompress->>Bitmap: write_RGB_row()
    else RGB (3 components)
        Decompress->>Decompress: read_scanline_3c()
        Decompress->>Bitmap: write_RGB_row()
    end

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 Four inks tumble, flipped and bright,
CMYK hops into RGB light,
Scanlines stretch, pixels reform,
A rabbit hums through color storm,
My palette grows — what a sight!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'added CMYK/YCCK support for JPGs' directly and clearly describes the main change in the pull request, which adds CMYK and YCCK color space support to JPEG handling.

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✨ Finishing Touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@addons/image/jpg.c`:
- Line 256: The allocation for data->row using al_malloc(w * 4) lacks a NULL
check; after the call to al_malloc (where data->row is assigned) add a check if
data->row == NULL and handle the failure by performing appropriate cleanup (free
any previously allocated resources), log or propagate an error, and return an
error code or goto the existing error/cleanup label so the subsequent writes to
data->row (currently at the code that writes data->row[x * 4 + ...]) cannot
dereference a NULL pointer.

[SiegeLord]

Thanks! This looks pretty good, I'll double check it later and we can merge it.