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Default BMP Multipliers Keyword

<DefaultBMPMultipliers F[,F] [options]>
<dbm F[,F] [options]>


    Default Bitmap Multipliers, both switch and parameter. See <BMPMultipliers> for multiplier description.  option can be used to set the stretch blt mode that affects how colors are sampled when images are shrunk and can be one of the values in the following table (YMMV but I find HALFTONE is the useful mode but if your machine is exceptionally slow by 2018 standards COLORONCOLOR is passable).  In addition to those options STAT is available (as of version 5.3.1.3) when <dbm> is used in frame that forces the current frame to use these multipliers and/or stretch mode (otherwise it/they would only become active in the next frame).  If STAT is used in the parameter line with this keyword all subsequent uses of it will be assumed to be STAT.  If you wish to specify a default stretch blt mode without affecting how all images are scaled you'll want to use a multiplier of 1 as in <dbm 1 HALFTONE> and if you wanted it active in the frame it occurred in you could use <dbm 1 HALFTONE STAT>.  See the Bitmap Notes for a discussion on the stretch blt mode.  From https://docs.microsoft.com/en-us/windows/desktop/api/Wingdi/nf-wingdi-setstretchbltmode:

Value Meaning
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.

Remarks

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.



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