The Crop tool allows cutting off an image. It helps to remove unwanted areas, to improve focus, or to make a square from a rectangular or contrariwise. To quickly access the tool use C.
Also, you can activate the Crop tool using the command Image -> Crop...
Using the Crop by Selection command in the Image menu, you can quickly remove parts of an image surrounding the selection.
Select an area you want to keep - drag while holding left mouse button.
When you click the image with the selected tool while holding down the Ctrl key, a crop frame around the entire image is created.
If there is an active selection on the image, the crop frame automatically appears around the selection area.
You can change the size of the area by dragging the markers on the sides and angles of the bounding frame. To constrain the proportions hold down Shift. To move the frame, place the cursor inside it and drag. If you move the cursor to the center point, it turns to an arrow with a circle : in this case, only the center is movable.
To rotate the area, place the cursor outside the frame, and move it with the left mouse button. If you press Alt, the rotation angle will change in 5 degrees. The frame rotates around the transformation center.
Note: Blue markers on the bounding frame indicate where will be the top of the cropped image.
If the frame is beyond the image, the empty area will be filled with a transparent background.
The basic tool settings are shown in the Tool Options panel above the Image Window. To display the full list of parameters, press the tool icon in the Tool Options panel.
The Ratio drop-down-list allows you to select the ratio to which you want to crop the picture.
If you want to crop an image by dragging the cursor over it, select the Freehand option.
If you would like your image to be cropped to a specific ratio, select the Custom option and enter the values in the Width and Height input fields.
If you want to keep the original aspect ratio fixed choose the Original option.
Other items in the list allow you to choose one of the most common aspect ratios.
Click on to rotate the crop frame by 90o.
In the Trim section, specify the crop mode:
Manual. The crop area is created using the cursor.
Trim Alpha. The crop frame is created using the alpha channel's information.
Trim Selection. The crop frame is created using the selection channel's information.
Top Left Color. Areas having the same color as the upper left pixel in the image will be placed outside the crop frame.
Bottom Right Color. Areas having the same color as the lower right pixel in the image will be placed outside the crop frame.
You can select the side from where to crop the picture: Top, Bottom, Left, Right. This option is disabled for the selected Manual mode.
The tool can work in two modes:
Remove External Area. The areas outside of the bounding frame will be deleted.
Hide External Area. The areas outside of the frame will be hidden but still accessible. This mode lets you correct the cropped area later - you can move the visible part with the Move tool.
External Area. The check-box helps to better visualize areas in and outside of the crop frame. If the check-box is enabled, the outer parts are highlighted in a selected color.
Adjust the visualization options for the external area:
Color. Click on the color square to open the Select Color dialog box.
Opacity (1-100). The parameter defines the transparency of the highlight color.
Show Grid. When the checkbox is active, a grid is displayed above the crop area, which helps when adjusting the crop frame.
To apply the tool and remove the areas outside the frame, click on OK or press Enter. To cancel the crop, press Cancel or use the Esc-key.