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Gimp erase to transparent all of one color11/29/2023 ![]() ( Normalize above works if the alpha channel you're recreating has at least some parts with 100% opacity if the image you're recreating is everywhere translucent, you can use Colors → Levels. You could also use the Channel Mixer instead, but it's a little trickier to use. To fix that, first desaturate the layer (using whichever mode that gives you the best contrast) and then use Colors → Auto → Normalize to make the background black. This gives you the alpha channel of the original image.Įdit: If your backgrounds are not black and white, the inverted difference layer won't have a black background. Take the difference of the layers: clone the black layer (you'll need it later), change the white layer's layer mode to "difference" and merge it down. The two layers should looks something like this: Move the white layer above the black layer if it's not already that way. or just open both and copy-and-paste one into the other). Open the black and white background versions as layers of the same image (using Open as Layers. Let me outline how it's done, using this image from Wikimedia Commons (by ed_g2s, licensed as CC-By-SA 3.0) as an example: That would be preferably PNG, but GIF would work as well.Yes, it's possible. to a file format which supports transparency. įinally, export the transparent image with File → Export As. ![]() Once the desired transparency area is selected, simply hit. When this happens, use +Drag with a Select tool of your choice to select a subtractive selection area. In this case, and barely visible, nine desired pixels in the middle of the pipe were also selected for deletion. Some of the desired image area might be selected as well because the colour matched. ![]() In between, hit + to undo.Īt times, it proves difficult to get the colour selection exactly right. Again, run a few tries while adjusting Threshold for best results. Nonetheless, do experiment with these settings and choose what looks best. For this particular example I chose not to apply Antialiasing nor Feather edges. This time around, do select Fill transparent areas as well as Sample merged. It might be tempting to perform Colour to Transparency, however this would also change semi-transparent areas within the desired image area. The right thing to do now is Select → By Colour. However, one can also use the eyedropper tool to pick a colour from anywhere on the desktop. Here, I used f3f3e9 as a background colour for plain colour filling. (In this respect, Adobe Photoshop is no different.) Hence, choose a colour which is compatible with the background on which the resulting picture will eventually be used.Ĭlick on the background colour rectangle in the upper half of the Tool Options toolbox window to change the background colour. Some colour mixing will be inevitable and even desired. Do select BG colour fill and Sample merged and run a few tries while adjusting Threshold for best results. Within the Bucket Fill toolbox options, select Fill transparent areas only when necessary. ![]() The next step is optional and consist in filling the area that should become transparent with a plain colour. This is done by selecting Layer → Tranparency → Add Alpha Channel. If this is the case, add an alpha transparency channel. Some image types lack a transparency channel JPG for example. ![]() Note: This tutorial is also available in PDF. ![]()
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