streakeagle

An advanced technique that makes the final files come out a little better is to work at higher resolutions, then resize the result down to the desired resolution.

Hello. You can use Adobe Photoshop or any other bitmap editor. I used Paintshop Pro. You resized the bitmap to a higher resolution with the same aspect ratio, i.e. if the original is 256x256 you could choose 300x300, 512x512, 1024x1024. If you double the pixels, the file gets 4x bigger, which takes more video memory. I suggest doubling the existing resolution for a first attempt.