![]() ![]() For a single layer, that means Select the background,Select>Grow by two pixels, andColors>Color to Alpha` but this will be long for 68 layers. So the light gray things will remain opaque, and we want to remove the background but prevent Color-to-alpha to change the light gray things into be partially opaque pixels. Export as GIF, don't forget to tick the animation checkbox, and to force all frames to 40ms (the optimization sets a longer interval).This will create a new image, use Filters>Animation>Playback to check it. Image>Interleave layers>Interleave single layer (sprite mode) and select the white layer.Add a layer filled with white (or your new background color).Dark grey can darken to black, but don't panic. Colors>Color to Alpha All layers and remove the background (color-pick, it should be #EEEEEE).Change image to full RGB: Image>Mode>RGB.This create a new image, you can close the source one. Remove the optimizations: Filters>Animation>Unoptimize.But in a GIF, there are no partially opaque pixels, they are fully opaque or fully transparent, so you can't have shadows. In the picture above the shadows would be implemented as partially opaque pixels, that would slightly darken the pixels of the background. When you want a transparent background, you want to be able to show the picture over any background. ![]() Then a transparent background is not doable for this particular GIF. Lower the newly created layer.It depends if the light gray things are shadows or not. Now create a New Layer (have Foreground set to Red when you do this). There should now be a nice green and alpha image with no trace of the blue left. Click OK after the color indicator on the Color To Alpha plug-in is changed to blue. If using Gimp for Windows, you’ll have to right-click on the destination button and select the Foreground - drag n’ drop doesn’t work. Click, hold, and drag from the color portion of this window to the color portion of the Color To Alpha plug-in. When you used the color picker to select the background, a window with the color popped up. Next use the Color Picker Tool to select the background color. If its not there, upgrade your gimp to 1.2.x. If its grayed-out, it means that you have an indexed image. Its menu location is Filters -> Colors -> Color To Alpha, where means to right click on the image. The first step is to activate the color to alpha plug-in. Instead, may I suggest the rest of the tutorial? Step 1 ¶ You can go too far, and blend it back to something close, but this is time consuming. Anything short of the rightmost image has some blue in the pixel, which will stick out. You can spend hours trying to find something that will work perfectly, but you won’t. You can try getting rid of all the ugly pixels, but then you’ll end up with something jagged like on the right. The middle one is close, but there are some ugly visible pixels still. This looks somewhat neat, but not what we’re going for. The left one has a blue border around it. When these are filled, we are left with flat black and slightly blueish-green pixels between them, or no transition to black at all.Ĭompare each with the target image below. You’ll note that each of the three zoomed in selections above have varying amounts of the green-blue mix selected. However, when removing an anti-aliased object from its background is not a good idea, as shown above. The common approach to doing many things in GIMP is to first get a good selection. This tutorial doesn’t address the complexities of handling real-world photos in this manner, but does briefly discuss it at the end. To illustrate this, this tutorial will use the above images as source and destination. The aim is to show the advantages of using the color to alpha plug-in over selection-based techniques. This tutorial shows you how you can efficiently replace the background of an image with another in GIMP, through the use of the color to alpha plug-in. Text and images Copyright (C) 2002 Seth Burgess and may not be used without permission of the author. ![]()
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