Technology

I'm probably gonna be massively downvoted for saying the forbidden word but I asked AI to do a summary with references of the forward and backward compatibility of PNG's new version:

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Based on recent search results, the new PNG specification (Third Edition) and its reference library (libpng) maintain strong backward compatibility while introducing modern features. Here's a detailed compatibility analysis:

🔄 1. Backward Compatibility (Viewing Old PNGs with New Lib)

• Full Support: The new libpng (1.6.49+) and PNG Third Edition fully support legacy PNG files. Existing PNGs (conforming to the 2003/2004 spec) will render correctly without changes .
• Implementation Stability: Libpng's API evolution (e.g., hiding png_struct/png_info internals since 1.5.0) ensures older apps using png_get_*/png_set_* functions remain compatible. Direct struct access, deprecated since 1.4.x, may break in libpng 2.0.x (C99-only) .
• Security Enhancements: Critical vulnerabilities (e.g., CVE-2019-7317 in png_image_free()) were patched in libpng 1.6.37+, making the new lib safer for decoding old files .

⚠️ 2. Forward Compatibility (Viewing New PNGs with Old Lib)

• Basic Support: Older libpng versions (pre-1.6.37) can decode new PNGs if they avoid new features. Core chunks like IHDR or IDAT remain unchanged .
• New Feature Limitations:
  • HDR Imagery: Requires libpng 1.6.45+ and apps supporting the mDCv chunk. Older libs ignore HDR data, falling back to SDR, which may cause color inaccuracies .
  • APNG Animation: Officially standardized in PNG Third Edition. Older libs (e.g., <1.6) treat APNG as static images, showing only the first frame .
  • EXIF Metadata: New eXIf chunks are ignored by legacy decoders, losing metadata like GPS or copyright info .
• Security Risks: Older libs (e.g., ≤1.6.36) contain unpatched vulnerabilities (e.g., CVE-2015-8126). Parsing malicious new PNGs could exploit these flaws .

📊 Compatibility Summary

🔧 3. Implementation and Industry Adoption

• Broad Support: Major browsers (Chrome, Safari, Firefox), OSs (iOS, macOS), and tools (Photoshop, DaVinci Resolve) already support the new spec .
• Progressive Enhancement: New features like HDR use optional chunks, ensuring graceful degradation in older software .
• Future-Proofing: Work on PNG Fourth Edition (HDR/SDR interoperability) and Fifth Edition (better compression) is underway .

💎 Conclusion

• Upgrade Recommended: New libpng (1.6.49+) ensures security and full compatibility with legacy files.
• Test Workflows: Verify critical tools handle new features (e.g., APNG animation in browsers).
• Fallbacks for Old Systems: For environments stuck with outdated libs, convert new PNGs to legacy format (e.g., strip HDR/APNG) .

For developers: Use png_get_valid(png_ptr, info_ptr, PNG_INFO_mDCv) to check HDR support and provide fallbacks .

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