GIMP Tutorial: How to Edit Screenshots

The GIMP is a free image manipulation program that runs on most operating systems, including GNU/Linux, Windows, Mac, and BSD. It is similar to Adobe Photoshop in many ways.

In an earlier tutorial, I described how to take screenshots in Linux. This tutorial describes how to edit those screenshots for posting on the web with GIMP.

Open your screenshot in the GIMP as shown below:

Cropping an image with the GIMP

Press the letter Ctrl-c to switch to the crop tool. Click-and-drag the mouse over the section of the screenshot that you want to keep as shown below. Then click on the "Crop" button.

Reducing the file size of a screenshot with the GIMP

Scale the Image

Find the scale image dialog on the menu: Image —> Scale Image. Then enter your desired dimensions for the image and click "Scale".

Reducing the Number of Colors

You can greatly reduce the file size by converting the image from RGB to Indexed, and reducing the number of colors to about 16 or 32 (or higher if you want your screenshots to look nicer). You can find that option on the menu: Image —> Mode —> Indexed.

In the image below I'm setting it to 16 colors, and turning off the dithering. The final image is not top-quality, but it's ok for screenshots when you need to keep the file size down.

Enhancing the Image

Update: I found a great tip on gimps.de that recommends enhancing resized images with the Unsharp Mask filter after scaling them: Filters —> Enhance —> Unsharp Mask. The Unsharp Mask will help reverse some of the blurring created by resizing the image. If making large scale changes to an image, scale it in steps to preserve quality.