I have linked before (March 14, 2013) to this github as a way to achieve atkinson dithered images for possible use in knitting. I received a post with questions on how to achieve this successfully. I work on a Mac, latest OS. The resulting dithered files were not read when downloaded by any app other than Preview, and resizing within program was poor quality. Here is my work-around: it is always best to resize any of the images to be processed in color or grey scale, before indexing modes or dithering. Once that is achieved, import image into github without changing output size in the program itself, and download. Your own image size will be retained. Now time for another freebie intervention: XnConvert will accept the file, convert it to BMP or other readable formats if preferred, resulting in a knittable image.
the sized image