The Crop Tool in GIMP allows you to easily change the size and shape of both a complete image and a single layer. The tool offers a number of options that allow you to make very accurate and precise crops of your images. You may want to crop a picture in preparation for printing, particularly if the print size has different proportions to the photos that your camera takes.
When you click on the Crop Tool in the Tools palette, represented by the scalpel icon, the Crop options appear below.
Current Layer Only
When checked, this option allows you to crop the active layer only, leaving the rest of the image unaltered. This can be very useful when you're producing a composite image, though obviously shouldn't be used if you are using GIMP to change the shape of a photo.
This option does affect the image as a whole and allows the crop tool to extend beyond the edges of an image. Because layers in GIMP can extend outside of the edge of an image, the new cropped image may include elements that weren't previously visible. However transparent pixels will appear if there are no existing pixels.
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Expand from Center
Normally, when you use the Crop Tool in GIMP, you start to draw the area to be cropped starting from one corner. If you select the Expand from Center option, the cropped area is drawn from the center outwards. This can be helpful if you need to precisely place an element of the picture in the center of the cropped image.
Selecting this option allows you more precise control over the shape that you crop. When the box is ticked, you can use the drop down to select Aspect ratio, Width, Height or Size. You can then use the input box below to specify the appropriate dimensions. For example, if you select Aspect ratio, you could input 3:2 into the box and this would crop the image to a shape suitable for printing as a six by four inch photo.
These two input boxes allow you to fine tune the position of the cropped area once you have used the GIMP Crop Tool to draw an area for cropping.
As with the Position input boxes, these two fields allow you to fine tune the size of the cropped area, either by entering values directly or using the up and down arrows to adjust the settings.
When selected, when you draw a selection with the Crop Tool, the area outside of the selected area is shaded out slightly to make it easier to focus on the selected area.
By default, this drop down is set to No guides, but you can also select Center lines, Rule of thirds and Golden sections. If you select one of the guides options, when you use the Crop Tool in GIMP, you'll see guide lines that can make it easier to place certain elements in the most attractive positions in your cropped image.
• More About Rule of Thirds
This button will only have an effect in certain circumstances. After drawing a crop selection, when clicked, if GIMP can find an area of pixels that contrast distinctly with the background, the crop area will be automatically shrunk to coincide with this area.
This operates with the Auto Shrink button and after using the Crop Tool, this will apply the Auto Shrink option to all visible layers. As mentioned above, the results will depend on the content of the image.