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. 90) will trim rather more than not enough. Typical values are between 10 and 20.
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.