The Transparent color space behaves uniquely in that it preserves the matte channel of the image if it exists.
The -colors or -monochrome option is required for this option to take effect.
-comment "%m:%f %wx%h"
0 No disposal specified. 1 Do not dispose. 2 Restore to background color. 3 Restore to previous.
-label "%m:%f %wx%h"
Letter 612x 792 Tabloid 792x1224 Ledger 1224x 792 Legal 612x1008 Statement 396x 612 Executive 540x 720 A3 842x1190 A4 595x 842 A5 420x 595 B4 729x1032 B5 516x 729 Folio 612x 936 Quarto 610x 780 10x14 720x1008
The optional mask can be used to provide matte information for composite when it has none or if you want a different mask. A mask image is typically grayscale and the same size as composite. If the image is not grayscale, it is converted to grayscale and the resulting intensities are used as matte information.