Copied from [[COM:VP]]
Unfortunately, there's a big problem with the thumbnailing of File:Shield of Trinity Aveling 1891.png. The current 595px thumbnail is a rather optimized 16bit grayscale+alpha image 82kb in size, while the 595px thumbnail under the new algorithm is a 32-bit RGB+alpha image 155 kb in size (or almost twice the filesize). It took about 6 years to get grayscale PNGs to generate grayscale thumbnails (one reason why some people still preferred GIFs for such images until relatively recently: File:Harleian Ms2169 St Mihell arms tricked original.gif etc.), and I would be quite disappointed to see such belated and hard-won progress suddenly be reversed at this point... AnonMoos (talk) 18:20, 13 July 2013 (UTC)
Note, we do store if a png file is RGBA or greyscale in img_metadata, so if we can't fix vips on this point, we could perhaps have it fallback to the old scaler for greyscale images.