Fix resizing animated WebP breaking animation#357
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ResizeImageAsync used a single MagickImage to read the file, which only reads the first frame of a multi-frame image. For animated WebP (and animated GIF), this discarded all subsequent frames and produced a static image on resize. Detect multi-frame images with the existing ImageAnalyzer.IsAnimated() helper and route them through a new ResizeAnimatedImageAsync method that uses MagickImageCollection: Coalesce, resize each frame, then write the collection back — preserving animation. Single-frame images continue through the original MagickImage path unchanged.
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Closes #258
Root cause
SaveImageFileHelper.ResizeImageAsyncreads the image with a singleMagickImage, which only reads the first frame of a multi-frame file. For an animated WebP (or animated GIF), every frame after the first is silently discarded, so the resized output is a static image.Fix
Detect multi-frame images using the existing
ImageAnalyzer.IsAnimated(FileInfo)helper (which pings the file withMagickImageCollectionand checksCount > 1). When animated, route through a newResizeAnimatedImageAsyncmethod that:MagickImageCollection(all frames).Coalesce()to expand frame diffs into full frames (per Magick.NET docs).Single-frame images continue through the original
MagickImagepath — no behavior change for PNG, JPEG, static WebP, etc.Notes
MagickImageCollectionpattern already exists in the codebase (TiffManager.LoadTiffPages,ImageAnalyzer.GetImageFrames), so this follows the established convention.ResizeImageAsync.This PR was prepared with AI assistance (code analysis and patch generation).