Using GIMP: Correcting and Touching Up Your Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 70

You have the option of cropping your image by entering values. You can
also crop your image by setting the margins. Click in the image and hold the
left mouse button and then drag the frame to the desired position.
For aspect ratio , you can choose any of the presets or enter you own value
in decimal notation (1.625) or as a ratio of two numbers (13:18). You can crop
the image without changing the aspect ratio by locking the aspect ratio .
You can reduce the size of your image by selecting the shrink factor. The
image does not need to be recalculated and image conversion is very fast.
All measurements are indicated in pixels. You can change the aspect
ratio for the printer or for the lab, but the program does not let you adjust the
setting to a specific size or resolution. You must use GIMP to edit the image
size and resolution as well as the print size.
Saving Your Image
When you have finished editing an image, you can hand it over to GIMP. You
can also save it as a stand-alone version directly out of UFRaw. The Save tab
offers you the following options:
• Path - The path to the folder in which you want to save the file.
• Filename - The name of the file.
• File type or format - The format in which you want to save it: PPM, PNG,
TIFF, or JPEG.
Compared to earlier versions, you don't have the option of choosing the color
depth (8 bits or 16 bits per channel). The images are saved with 24 bits (8 bits
per channel). The first three are high-quality formats. GIMP can read all these
formats, but TIFF and PNG are the best options (high quality and widely used)
for exporting into other programs.
If you want to save in JPEG, you can select the compression size. Leave it at
the default setting of 85% or set it to the maximum level of 100%. You will find
more on this topic later in section 2.5.12. If you want to use the image for the
Web, choose the JPEG progressive encoding option.
Figure: 2.12
The Save tab with the file type settings, filename, and path