GIMP Casual User Series — The Crop Tool
Do you have minimal experience with GIMP, but would like to know more about the best tools to use for trimming photos? Are you interested in learning about the various options that make these tools easier to use? Would you like a method for making a decision about which tool is best for which type of job? If so, read on for an exploration of the first tool in this series — the Crop Tool.
|Giraffes cropping grass|
For this article, I'll be using GIMP 2.8 and a photo of some giraffes, which you can download by clicking on the picture. (When you get to the full-sized image, drag it and drop it on your desktop.) It is assumed that you have some basic knowledge about GIMP, such as how to invoke it and load an image, how to navigate the menus, and how to save a file. By the end of this article you should have a good feel for using the Crop Tool, along with all of its options that are applicable to cropping photographs.
The Reference Picture
The rest of this article will refer to this image when discussing various aspects of the Crop Tool.
|GIMP's Crop Tool|
Let's say you want to cut out the adult and baby in the center of the picture. Select the Crop Tool  (shortcut Shift+C). Left-click in the image above and to the left of the center giraffe, then drag down and to the right to create a rectangle. Notice that the unselected part of the photo darkens  so that the area you're selecting stands out. The selection box that you created will have handles  along the edges and in the corners. If you left-click inside of a side or corner handle, you can drag it to change the size of the selection box. You can move the selection box without changing its size by left-clicking in the central area and holding the mouse button down while dragging the box around. Take note of how the cursor changes when you move the mouse into each of the various zones of the selection box. When you're satisfied with your selection, left-click quickly inside the selection box or press the Enter key to crop the picture.
Now let's take a look at the options for the Crop Tool, which are displayed in the Tool Options pane, which is usually found in the Toolbox pane. If you don't see the Toolbox pane, select Windows > New Toolbox (shortcut CTRL+B) and resize the Toolbox pane to something useful. If you don't see the Tool Options pane, then select Windows > Dockable Dialogs > Tool Options. This will open a separate Tool Options pane. You can dock it in the Toolbox pane by grabbing the Tool Options tab inside the pane and dragging it to the lower section of the Toolbox pane.
Use CTRL+Z to undo the crop you did previously, then use the Crop Tool to make a selection box again. Grab a selection handle and resize the box. Notice how the numbers change in the Size fields  of the Crop Tool Options. Grab the selection box in the middle and slide it around. Notice how the numbers change in the Position fields . If you want to make very small adjustments to the size and position of the selection box, you may find it easier to change the numbers in the Size and Position fields instead of trying to drag the selection box with the mouse. Or, if you have specific dimensions that you want to use for cropping, enter them in the Size boxes, then grab the selection box and move it around until you like the composition. The drop-down boxes next to the Size and Position fields let you choose from among a number of units; for example, pixels, percent, or inches.
Another way to affect how the selection box size changes is to check the Expand from center option . When this option is on, grabbing a handle on the side and moving it will cause the opposite side to move the same amount in the opposite direction. Grabbing a corner will cause all four sides to move in unison.
Now grab the top handle and slide it upward. Notice that it stops at some point. This is because the bottom of the selection box has hit the bottom of the picture. By default, the selection box will not move outside the bounds of the picture. This behavior is controlled by the Allow growing option . Turn this option on, then drag the top handle upward and see that it now moves freely because the bottom handle goes below the picture.
You can add even more control to how the selection box changes by turning on the Fixed option . The drop-down list next to it lets you select Aspect ratio, Width, Height, or Size. Aspect ratio keeps the width and height of the selection box in the same proportions no matter which handle you use to change the size. You can specify a specific aspect ratio by entering one in the associated number box; for example, "3:4". Clicking on the portrait or landscape button will change to the opposite aspect ratio and flip the numbers. Note that usually the selection box over the image will not change size until you select a handle and move it.
The Fixed Width, Height, and Size options are also controlled by the number box. Width and Height are specified as single decimal numbers in any of a number of units that you can select from the drop-down list next to it. Size is specified as width x height (for example, 1000x500), is always in pixels, and can be changed to portrait or landscape mode just like the Aspect ratio option.
If you need some guidelines to help you line things up in your selection, you can choose from among several guides in the Guides drop-down list . The Center lines option gives you a crosshair to help you center the selection box. The Rule of thirds option gives you two horizontal and two vertical guidelines that divide the selection box up into a 3x3 grid. The Rule of fifths option divides the selection box up into a 5x5 grid. The Golden sections option is similar to the Rule of thirds, but the central sections are smaller than the outer sections. The Diagonal lines option shows diagonal lines coming from each corner of the selection box. If your selection box is a square, they'll form an X crosshair; otherwise, you'll see two parallel lines going along each angle.
|Rule of Thirds|
|Rule of Fifths|
If you want to turn off darkening of the unselected part of the photo, simply turn off the Highlight option .
It is unlikely you'll be interested in using the remaining options, Current layer only and Auto Shrink, with simple photos, but I'll describe them here for completeness.
The Current layer only option is useful only when you have an image with multiple layers. By default, the Crop Tool will crop all layers. If you want to crop only the current layer, turn this option on.
The Auto Shrink button causes GIMP to attempt to locate a border in the active layer inside the current selection box to which it can shrink the selection box. This option works well only with isolated objects that contrast sharply with the background. Turning on the Shrink merged option causes GIMP to take into account all visible layers instead of just the currently active layer.
Continue experimenting with the Crop Tool until you feel confident in your use of it. Don't forget that you can zoom in (CTRL+Mouse Wheel Forward) to make it easier to make small adjustments to the size of the selection box. If you have any questions about this tool, please leave a comment or send me a message.
Related GIMP Articles
GIMP 2.8 Tutorial: Which Tool Should I Use to Crop a Photo? -- Part 2
GIMP 2.8 Tutorial: Which Tool Should I Use to Crop a Photo? -- Part 3
GIMP 2.8 Tutorial: Which Tool Should I Use to Crop a Photo? -- Conclusion