It will open a window. Now, click on the Palette scroll, and click on "Exact". Alternatively, if the image has too many colours (more than 256), click on "Local (Perceptual)". Then, click "OK". Note that if your image has too many colors, it will be subject to what we call colorloss, and will result in something ugly. There are ways to avoid this, and we will abord this in the chapter "Avoiding colorloss".- The image is now in indexed colors, but with a bad palette. Let's open the palette. Click on Image -> Mode -> Color Table.
ummm there isnt a "palette scroll" option in gimp
I AM evil! Stop Laughing!!