You can crop the image with greater precision by cropping by value.
Method. Select a cropping method, either to (to specify the resulting size) or by (to specify how much to remove).
Amount. Enter a cropping amount (determined by Units: pixels or % of image).
Units. Select a unit for the cropping operation (either in pixels or % of image).
Orientation. Select an orientation for cropping. This always specifies the direction from which pixels will be removed from the image. For horizontal cropping, the values are from left, from right and centered. For vertical cropping, the values are from top, from bottom and centered.
Add Border. Check this option to enable border additions. Negative values are required in the Amount fields to add borders.
Border fill color. Use this button to select a color for any added borders.