JPEG images are a good data format for photographs because they contain data that is compressed in a manner optimized for the human eye. However, it is a “lossy” compression, meaning that if they are unencoded and re-encoded several times, the image will lose quality.
Sometimes all I want to do is crop a picture, to chop off uninteresting areas of the photo. Several tools can do this by working on the native JPEG data, meaning there is no loss of information from re-encoding the image.
The command-line tool jpegtran is designed to make a number of transformations to JPEG pictures with no data loss, including rotation and cropping. However, being a command-line tool, it requires you to specify x and y coordinates to crop. It is not convenient to visually pick a section of a picture to save.
A Windows application called jpegcrop gives you the ability to display a JPEG picture on the screen and select the portion to crop out. It saves the cropped section as a new file, or you can overwrite the original file if you prefer. It even preserves the EXIF metadata of the original file. For Linux, I have not found a native graphical application like Jpegcrop, but Jpegcrop for Windows runs just fine on Linux using Wine.
Submitted by amillar on Sun, 2006-01-29 09:59