This is the standard bitmap format supported by Microsoft Windows. ThumbsPlus supports all color depths (1, 4, 8, 16, 24 or 32 bit), and the compressed (RLE) formats for 4-bit (RLE4) and 8-bit (RLE8) bitmaps.
BMP files compressed with video codecs or JPEG are not yet supported.
The standard VGA driver does not properly decompress 8-bit compressed BMP files; for best color viewing (and nicest thumbnails), you should load a 256-color or higher Windows video driver, which should eliminate this problem.
ThumbsPlus currently writes only uncompressed BMP files.
Note: TNB files are simply bitmap files with a .TNB extension.