![]() 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. So instead so using the Dog image as the top layer, I created a layer with pure red, ff0000.Note: This tutorial is also available in PDF. Then I had the idea that using one image to erase colors on the other one was making it too complicated for seeing what is going on. A precise color match would, at the very least, mean the 6 hexadecimal digits for the RGB match precisely, otherwise nothing is erased. 4 channels at 8 bits each gives you 32 bits, so we call these 32-bit color. 16 x 16 = 256, and we know that it is handled in binary mathematics by one 8-bit byte. Recall that digital images are defined by numbers that express the Red, Green, Blue, and Alpha, and each number is composed of two hexadecimal digits. I think there is something going on involving the numbers here. I don’t think it is as simple as just looking for a color match between the two images. Now the problem I have with this mode is that the GIMP team has not gotten around to documenting it, so I was not (at first) certain exactly how this color erase really works. I then reduced the opacity of this top layer to 75%, and got an image with the bottom showing up through the top. I selected my top layer, the Dog photo, and left it in Normal mode. It is worth noting that this mode, like many of the Layer modes, can also be applied to Brushes which allows you to use it just in certain areas, but first let’s discuss doing it as a Layer mode. This mode dissolves the Top layer into the Bottom layer by means of partial transparency. And if we reduced the opacity of the Top layer or added some areas of transparency, then of course some of the Bottom layer would show through, but none if it comes through solely because of the Layer mode. If the Top layer was smaller than the Bottom layer, the areas not covered by the Top layer would show through. ![]() So the result is a nice picture of a dog. ![]() This means that the Top layer will entirely cover the Bottom layer in the resulting image because there is no transparency in the Top layer. And note that the Mode selected is Normal. Here we see the layers open in GIMP in the order I specified.
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