XmNimageMapToPalette
This resource determines if a XmHTML widget should perform dithering to a fixed palette and if so how that should be done.
Possible values are:

XmQUICK A closest distance algorithm is used to map image colors to the palette. No error correction is performed. Fast, but the resulting image quality depends on the distribution of the colors in the image.
XmBEST Ordered dither using predefined error matrices. Offers the best balance between speed and quality but uses a lot of memory (512kb).
XmFAST Simple ordered dither without error correction. This is the fastest method but uses a lot of memory (512kb).
XmSLOW A closest distance algorithm followed by Floyd-Steinberg error diffusion. Slowest method but highest quality.
XmDISABLED disables palette mapping. This is the default setting.

XmQUICK	A closest distance algorithm is used to map image colors to the palette. No error correction is performed. Fast, but the resulting image quality depends on the distribution of the colors in the image.
XmBEST	Ordered dither using predefined error matrices. Offers the best balance between speed and quality but uses a lot of memory (512kb).
XmFAST	Simple ordered dither without error correction. This is the fastest method but uses a lot of memory (512kb).
XmSLOW	A closest distance algorithm followed by Floyd-Steinberg error diffusion. Slowest method but highest quality.
XmDISABLED	disables palette mapping. This is the default setting.