Determines the method to use for comparing pixels when determining whether to expand the viewport.

The following options are available:

Match color

Uses an exact match of the RGB value of the pixel’s color.  When in 8-bit mode this will perform a palette lookup and use the RGB value of the palette entry to perform the comparison.  In 16 or 15 bit mode this will convert the pixel to 32-bit color before comparing.

Color less than or equal

Matches if all of the R, G, and B channels match or are less than the comparison value, converting the pixel as described in “Match color.”

Color greater than or equal

Matches if all of the R, G, and B channels match or are less than the comparison value, converting the pixel as described in “Match color.”

Match palette entry

In 8-bit mode, uses the palette index of the pixel for comparison.  In other modes, uses the numeric value of the pixel for comparison, matching at most 24 bits.

Palette less than or equal

Matches if the palette index or pixel’s numeric value matches or is less than the comparison value.

Palette greater than or equal

Matches if the palette index or pixel’s numeric value matches or is greater than the comparison value.

Match 3 palette entries (8-bit only)

In 8-bit color mode, matches up to 3 palette entries.  These should be packed in the comparison value.  For instance to match palette entries 1, 5, and 12, use value 01050C.  If you need to match only 1 or 2 palette entries, duplicate the numbers, for instance to match entries 15 or 127 use 0F0F7F.
In other color modes, functions the same as “Match palette entry.”