BMP

Egami reads Windows bitmaps with core, info, V2 to V5 and OS/2 2.x headers at 1 to 32 bits, RLE4, RLE8 and RLE24, OS/2 Huffman 1D, bit fields, embedded PNG and JPEG and V5 ICC profiles. It writes 24-bit, 32-bit with alpha, 16-bit 5-5-5, 5-6-5 and 1-5-5-5, and 1, 2, 4 or 8-bit palettes, the 4 and 8-bit ones optionally run-length encoded, with resolution and ICC.

A BMP loads as Bgr8, or Bgra8 with alpha.

// Auto (the default): 24-bit when every pixel is opaque, 32-bit with alpha otherwise.
image.Save("duck.bmp");

// A 16-color palette, built from the image and dithered.
image.Save("duck-16.bmp", new BmpWriterOptions { PixelFormat = BmpPixelFormat.Indexed4 });

// The same palette, run-length encoded (RLE4): smaller where the image has flat areas.
image.Save("duck-16-rle.bmp", new BmpWriterOptions { PixelFormat = BmpPixelFormat.Indexed4, RunLength = true });

A plain 32-bit BMP's fourth byte is used as alpha unless it is 0 in every pixel, in which case the image loads opaque; an alpha mask in the header is always used. Pixels that an RLE delta skips are black. BmpPixelFormat.Indexed2 writes Windows CE 2-bit files, which many desktop readers cannot open, so Auto never picks it. Bgr555 writes the default 16-bit layout with no bit fields; Bgr565 and Bgra5551 write a V4 header with bit-field masks. Loading a 16-bit file as Bgr555, Bgr565 or Bgra5551 copies its rows when the masks match the type. Resolution is written in pixels per meter, and an ICC profile switches the header to V5 with the profile embedded.

BmpWriterOptions.RunLength writes Indexed4 and Indexed8 as RLE4 and RLE8: runs of one index (and for RLE4 two that take turns) as a count and the index, the rest as absolute runs, an end of line after each row and an end of bitmap after the last. Images with flat areas shrink a great deal; noisy ones can grow a little. Absolute RLE4 runs are kept to an even length, since Pillow drops the last index of an odd one; ImageMagick and Pillow read the files with the same pixels. Other layouts cannot be run-length encoded, and asking for it throws ArgumentException.

OS/2 Huffman 1D files (compression 3 under an OS/2 2.x header, 1 bit a pixel) hold CCITT T.4 one-dimensional rows, which Egami's CCITT decoder reads with or without EOL codes before the rows, or byte-aligned as TIFF's modified Huffman. White runs are palette entry 0 and black runs entry 1; the BmpDetails.Compression of such a file is Huffman1D. Rows the data does not reach are left black with the Bmp.RowsMissing warning, or throw in strict mode.