Make the Frame struct Pixel-agnostic?

[moulins]

The Frames returned by AnimationDecoder are hardcoded to contain Rgba8Images, which is generally suboptimal when working with animated PNG or WEBP images:

• if the source image has no alpha channel, this imposes an extra conversion;
• 16-bit APNGs are unsupported because of this.

Would it make sense to have Frame contain a DynamicImage instead of a Rgba8Image, despite the fact that this is a breaking change? Existing users of the API could easily upgrade by doing the conversion to Rgba8 manually with .into_buffer().into_rgba8() or similar.

[kornelski]

It would be nice to have.

It might be doable in a backwards-compatible way by adding a new method next to into_frames, like into_frames_dynamic().

However, I don't think it has practical utility besides optimization for opaque RGB8. AFAIK WebP doesn't have 16-bit coding — lossless is 8-bit-only, and VP8 implementations don't even use full range in 8 bits. PNG compression is pretty bad in 16 bits.

[moulins]

You're right that this would be mostly for optimization purposes; another theoretical use-case would be grayscale APNGs, but I'd be surprised if they actually exist in the wild ^^