No alpha layer when saving webp

[kattjevfel]

WebP supports an alpha layer both in lossless and lossy form*, though when exporting as webp it is saved as if it were a jpeg, a white background.

Here I show an image converted with imagemagick, output from waifu2x-converter-cpp and finally the source image.

• https://developers.google.com/speed/webp/docs/webp_lossless_alpha_study