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carol.gimp.orgGIMP BasicsLite Quickies |
Problem: you want to add some text to an image but find that the font draws itself all jagged or you would like to run a filter over the image but find that the filter is "grayed" out in the image. These problems are more often than not caused by the mode of the image. Before you do any sort of manipulation to any image with TheGIMP, it is very important to make certain that the mode of the image is RGB and not indexed.
Indexed or RGB modes are the names of two different ways the image handles color information. Indexed has the good quality of being very lightweight, which can be seen in the size of the image. Indexed mode has the bad quality of only using 256 colors; this means a lot of approximation to reduce the colors to so few. RGB has the bad quality of being a heavier weight; the good part being that the format uses millions and millions of colors -- much less approximation.
You can search the web for the definitions and study color theory on your own; new users of TheGIMP should make certain the mode of your image is RGB before working on it, simply.
For this demonstration, an old images from APOD, back from the days of small computers and slow internet connections. Originally appearing June 22, 1995 and reappearing larger yet still indexed on October 26, 1997 a little larger, the famous photo of the earth taken from Apollo 17.
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Change to RGBIt is so simple to change the mode of an image to RGB that it hardly makes a whole section to this tutorial worth it, however, it is so important that the importance overrides the simplicity. Simply right click with the mouse on the image and follow the menu path <Image> Image ->Mode ->RGB. |
Change to IndexedSo much more complex to make an image simpler -- you get a few more choices when reducing an image from millions of colors to only 256. Using the same image, only this time grabbed from Earth Observatory in full RGB and really really big, a demonstration of converting from indexed back to RGB. Right click on the image and follow the menus <Image> Image ->Mode ->Indexed ... (the three dots at the end of the menu entry tell you to expect a dialog). Trust the default settings and touch the "Ok" button with the mouse. Convert from RGB to indexed only as a last step with TheGIMP. If you are saving your image as a GIF, you will need to take this step. If you are not so worried about perfect color information and more about file size, saving as an indexed PNG is the best option. |
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RGB to GrayscaleThe quickest way to change your photographs from color to "black & white" is to follow the menu <Image> Image ->Mode ->Grayscale. If you would like photographs that seem more like those really wonderful old black and white prints you will need to use some tools that are beyond the scope of this new users tutorial. The ideal use for this mode is to save scanned documents and line drawings with. |
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