Removes single-colour frame around the image.
The parameter does not specify the amount of border or frame to trim but rather how aggressive the trim algorithm should be. A bigger value of the parameter (e.g. 25) will trim rather more than not enough. Typical values are between 0 and 10.
This allows you to use the same parameter values for all your images.
If the image is resized with the width and/or height commands, the resizing is performed after the border (if present) is trimmed.