The BMP RLE 4 Compression Algorithm
--- BMP RLE_4 compression
RLE_4 compression knows the two modes of the RLE_8 compression,
absolute and RLE. In the RLE mode, the first byte contains the count
of pixels to draw, the second byte contains in its two nibbles the
indices off the pixel colors, the higher 4 bits are the left pixel,
the lower 4 bits are the right pixel. Note that two-color runs are
possible to encode with RLE_4 through this.
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