Append Preserve

The append-preserve parameter keeps the base image’s size along the shared edge, clipping the append image rather than growing the canvas to fit it. It is a boolean and defaults to off.

Without it, appending a taller image to the right grows the canvas to the taller of the two, leaving empty space beside the base image. With append-preserve=true, the output keeps the base image’s height and the appended image is cropped to match.

Edit in Sandbox

Edit in Sandbox

For a side append the preserved dimension is the height; for a top or bottom append it is the width.