UltraSlim for Android converts JPEG, HEIC, AVIF and JXL with Ultra HDR

⚡ The gist in 5 seconds - UltraSlim, an offline photo converter for Android with mutual conversion between JPEG, HEIC, AVIF and JXL, has been published on GitHub. - The key feature is preserving Ultra HDR and gain maps per the ISO 21496-1 standard when re-saving. - Batch processing and background conversion are claimed; everything runs fully locally, with no network access. ### 🔍 What was found The linyusenzz/UltraSlim project has been published on GitHub as an image transcoding utility for Android. The repository description lists four formats — JPEG, HEIC, AVIF and JXL — with mutual conversion between them. It specifically emphasizes that when re-saving, Ultra HDR and gain maps are not lost per the ISO 21496-1 specification: that is, the HDR component of the image is carried over into the output file rather than discarded, as usually happens with ordinary re-encoding. All processing happens offline, on the device. Among the claimed features are batch mode (processing a set of files in one pass) and background conversion — meaning tasks don't block the interface and keep running while the user is busy with something else. Specific app versions, build numbers, and menu paths are not given in the source — only the fact of the repository's publication and the list of features. ### 💡 Why it matters Ultra HDR and gain maps are exactly what most often gets lost during conversion: ordinary transcoders simply throw away the HDR metadata, and a phone photo turns into a flat SDR file. The utility addresses a narrow but painful scenario: converting a library from HEIC to more universal JPEG or space-efficient AVIF/JXL without losing the HDR layer and without sending private photos to a third-party server. AVIF and JXL are still unevenly supported across Android, so a local converter is a practical workaround for anyone keeping an archive of photos in a single format.