ImagePad¶

Pads an image on each side. A single extent pads all four sides, with black as the default fill:

$ wo 'ImageData[ImagePad[Image[{{0.5}}], 1]]'
{{0., 0., 0.}, {0., 0.5, 0.}, {0., 0., 0.}}

Per-side extents are given as {{left, right}, {bottom, top}}:

$ wo 'ImageDimensions[ImagePad[Image[{{0.1, 0.2}, {0.3, 0.4}}], {{1, 0}, {0, 2}}]]'
{3, 4}

A third argument gives the fill: a constant value, or one of the edge-extension methods "Fixed", "Periodic" and "Reflected".

$ wo 'Round[ImageData[ImagePad[Image[{{0.2, 0.4}}], 1, "Fixed"]], 0.001]'
{{0.2, 0.2, 0.4, 0.4}, {0.2, 0.2, 0.4, 0.4}, {0.2, 0.2, 0.4, 0.4}}

A negative extent trims that side instead of growing it.