|BLACKONWHITE||Performs a Boolean AND operation using the color values
for the eliminated and existing pixels. If the bitmap is a monochrome
bitmap, this mode preserves black pixels at the expense of white pixels.
|COLORONCOLOR||Deletes the pixels. This mode deletes all eliminated
lines of pixels without trying to preserve their information.
|HALFTONE||Maps pixels from the source rectangle into blocks of
pixels in the destination rectangle. The average color over the
destination block of pixels approximates the color of the source pixels.
|WHITEONBLACK||Performs a Boolean OR operation using the color values for the eliminated and existing pixels. If the bitmap is a monochrome bitmap, this mode preserves white pixels at the expense of black pixels.|
The stretching mode defines how the system combines rows or columns of a bitmap with existing pixels on a display device when an application calls the StretchBlt function (that DMDX uses when stretching bitmaps).
The BLACKONWHITE and WHITEONBLACK modes are typically used to preserve foreground pixels in monochrome bitmaps. The COLORONCOLOR mode is typically used to preserve color in color bitmaps.
The HALFTONE mode is slower and requires more processing of the source image than the other three modes; but produces higher quality images.
Note that the default mode appears to be BLACKONWHITE, didn't find anywhere that defined it as such but visual inspection of the artifacts leads me to conclude it's so.