Originally Posted by DNSB
As per a PM which asked just what I meant by blockiness, I've attached 3 images to this message. The first (cover.jpeg) is the original cover that my daughter obtained when she picked up Catching Fire. The second is the image converted to 4 bit B&W (16 level greyscale) without dithering -- this is very close to what the colour cover image looked as rendered by the Kobo. The third is the image converted to 4 bit B&W with dithering. The fourth image (catching_fire.jpg) is the final version we used with smoothing, resizing, contrast and brightness changes.
Notice the banding around the mocking jay in the second image visible even in the thumbnail and the artifacting around Suzanne Collins' name in images 2 and 3 if you view the full size image.
So you're saying the Kobo's so sub-optimal greyscale conversion / it's better to upload covers / images already converted to greyscale my Calibre?