A Gerrit change reveals the technical reality behind Chrome's JPEG XL support: incremental integration work that never reached stable users, showing how browser feature development actually happens behind the scenes.
The commit message "Wire up JXL decoder" (Gerrit change 7184969) tells a deceptively simple story about one of Chrome's most controversial feature additions. This single line represents months of engineering work that ultimately became a case study in how browser vendors make decisions about new image formats.
What Was Claimed
In 2021, Google announced support for JPEG XL in Chrome, positioning it as a next-generation image format that offered lossless JPEG transcoding, progressive decoding, and superior compression ratios compared to existing formats. The marketing emphasized performance gains and forward-looking capabilities.
What Was Actually New
Change 7184969 wasn't the beginning or the end—it was part of a multi-phase integration that started with adding the jxl decoder to Chrome's image pipeline. The technical work involved:
Codec Registration: The change connected Chrome's existing JPEG XL decoder library (developed separately) to the browser's image loading infrastructure. This meant registering image/jxl as a supported MIME type and ensuring the browser could route JXL files through the proper decoding pipeline.
Blink Integration: The work touched Blink (Chrome's rendering engine) to handle JXL images in HTML, CSS backgrounds, and <picture> elements. This required modifying the image resource loader to recognize .jxl extensions and handle them alongside .jpg, .png, and .webp.
Platform-Specific Decoders: Chrome uses platform-native decoders where available for performance. The integration had to account for fallback paths when OS-level JXL support didn't exist, routing those cases through Chrome's software decoder.
The Technical Reality
The "wire up" work reveals how browser features actually ship:
Behind Feature Flags: Even after the decoder was connected, JXL support remained behind the --enable-features=Jxl flag. This allowed testing without exposing users to potential bugs or performance regressions.
Incremental Rollout: The Gerrit changes show a pattern common in large codebases—small, focused commits that gradually build functionality. One commit wires up the decoder, another adds tests, a third handles edge cases in the decoder pipeline.
Dependency Management: Chrome's JXL support required coordinating with the libjxl reference implementation. The integration work included build system changes to include the library and ensure it compiled across all Chrome's supported platforms.
What Never Shipped
Despite the engineering work, Chrome's JXL support never reached stable channels. In February 2023, Google removed the code entirely, citing:
- Lack of ecosystem adoption: No major image editing tools exported JXL by default
- Performance concerns: The decoder didn't provide clear wins over existing formats
- Maintenance burden: Supporting an additional format required ongoing engineering resources
Lessons for Developers
The JXL integration story demonstrates several patterns relevant to software development:
Feature Flags Are Safety Nets: The Gerrit history shows how feature flags allow teams to merge incomplete work, test it in real environments, and make go/no-go decisions without long-lived feature branches.
Integration Complexity: "Wiring up" a decoder sounds trivial but touches multiple subsystems—network stack (for downloading), cache layer, rendering engine, and platform-specific code paths.
Ecosystem Matters More Than Technology: JXL's technical merits were real, but without tooling support and industry buy-in, browser integration alone couldn't drive adoption.
The change 7184969 represents engineering effort that ultimately served as a learning exercise rather than a shipped feature—a common outcome in platform development that rarely gets discussed publicly.
Related Resources
- Gerrit Change 7184969 - The original integration patch
- libjxl Reference Implementation - The JPEG XL decoder library
- Chromium Feature Status - JXL feature tracking (archived)
- Removal Commit - Where JXL support was removed
- Blink Image Pipeline Documentation - Understanding how Chrome handles image formats
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