GIMP Help ► Separating single-layer bitmaps into layered PNGs w/optional transparency

In many ways I shouldn’t even need to be posting this to Sitepoint, but for the life of me I can’t seem to locate a step-by-step instruction page that isn’t either a flash movie (I don’t want) or worse, a tutorial on transparency in which the sample image conveniently has rgb values so dissimilar that even a complete imbecile would grasp the concept of making one of them transparent. But what if you’re modifying a GIF image (an icon, for example) that has a background pattern you’d like to remove?

Let’s assume the GIF you’re working with was rendered flat (non-transparent) and your objective is to convert it into two PNGs — 1 with the MS 16-Color Background Champion PUKE (#808000) and 1 with the traditional PNG background for transparency, checkered.

Attached are two versions of a Square thumbprint icon: a 128px PNG . . . and the same image in GIF, deliberately enlarged to 512px to aggravate the image’s anti-aliasing, and then further compromised by the 32-color restraint of the format. This is an image I have no intention of using myself, it just happens to present one of the worst-possible conversion projects I hope never to have to face. I figure it must be downhill from here! :stuck_out_tongue:

My preference is to locate a tutorial that doesn’t cheat the issue by using a 2-step clean original, but courageously tackles something as mangled as the GIF blowup I just attached. I know you experts here will help me (you always do), but what would really be even better is to share with me your favorite GIMP site for the serious Beginner such as myself. It is so frustrating that these “How To” GIMP pages seem always to be populated with clean vectors, instead of drilling down to transparency technique for the more complicated conversion/recovery projects.

Sorry this was so long! I thank the members in advance for sharing (anything) you think would be helpful. I guess that includes addons/plug-ins . . . but really I want first to have a firm grasp of transparency in this wonderful product.


I don’t know that I would try and disentangle this in gimp. For the example cited I would probably use ImageMagick to set the diagonal grey bands to the background colour. This will recover the fingerprint but not the grey diagonal bands.

You could use Gimp and fix the image up with painstaking brush work. (Sorry, I dont know a better way with Gimp.) Even though I have used Gimp in the past I found so many “gotchas” that I abandoned it for Inkscape. Some people’s experience may differ but thats me.

Sent from my XT316 using Tapatalk 2

Inkscape? Hmm . . .