CHAPTER 8 (Web site template) COLOR MANIPULATION, CHANNELS, AND LAYER
CHAPTER 8 COLOR MANIPULATION, CHANNELS, AND LAYER MODES 321 If you can change the design to eliminate shading, you can make a much smaller image. In Figure8-25, all the shading (except in Wilber himself) has been removed and the image converted to indexed with no dithering. This resulted in a GIF file less than 5K, as compared to 6.1K for the dithered version and 15.8K for the image from Figure 8-24. Figure 8-25. Shading removed, converted as eight colors with no dithering Doubtless you re wondering, Why all this fuss over a mere 10 kilobytes? But some web pages have hundreds of images on them. If you design your icons to have small file sizes, that can make the difference between a web page that loads instantly and one that loads so slowly that users give up on it and go someplace else. Tip Do you ever find that the GIMP function you want to use is grayed out when you re working with an image you loaded from a GIF file? Most often, this is because your image is in indexed mode, perhaps because it was originally a GIF image. Many of GIMP s color functions will only work on an RGB image (or sometimes a grayscale image), and will be disabled for indexed images. (This is because an indexed image does not allow a full range of colors.) If you see color functions disabled and wonder why, check the title bar of the image window and see if it says Indexed. If so, a quick conversion (using the Mode menu) back to RGB mode will solve the problem. (If that doesn t enable the function, check whether the image has an alpha channel; some filters require one.) Of course, if you ultimately want to save to GIF or indexed PNG, you ll have to convert back to indexed mode before you save. Editing the Palette What if you want to change one of the colors in an indexed image? Dialogs . Colormap brings up the colormap editor (Figure 8-26). This window shows every color currently in the image. To change a color, simply double-click on the color square to bring up a color chooser. Alternatively, click on a square and then edit the HTML notation box and hit Return. Or click on a color, and then click the lower-left button in the dialog, Edit color.
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