Resizes (by pixel dimension count) both the horizontal and vertical dimensions of the image. If you resize the image larger, the extra space is filled with the current background color. You can also change the color depth at the same time or crop to an existing marked rectangle.
The field described as “Enlarge to contain all shapes” becomes active if any shapes (lines, rectangle, texts etc.) you have drawn over the image extend beyond the actual image area. You may select this option to enlarge the image to contain all such shapes. The space added is filled with the current background color, which you may set under “Edit” tab of the ribbon, in the “Color” group – for example the image below shows white as the current background color.