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2.1.1.7 Compression Enumeration

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The Compression Enumeration specifies the type of compression for a bitmap image.

 typedef  enum
 {
   BI_RGB = 0x0000,
   BI_RLE8 = 0x0001,
   BI_RLE4 = 0x0002,
   BI_BITFIELDS = 0x0003,
   BI_JPEG = 0x0004,
   BI_PNG = 0x0005,
   BI_CMYK = 0x000B,
   BI_CMYKRLE8 = 0x000C,
   BI_CMYKRLE4 = 0x000D
 } Compression;

BI_RGB: The bitmap is in uncompressed red green blue (RGB) format that is not compressed and does not use color masks.

BI_RLE8: An RGB format that uses run-length encoding (RLE) compression for bitmaps with 8 bits per pixel. The compression uses a 2-byte format consisting of a count byte followed by a byte containing a color index.

BI_RLE4: An RGB format that uses RLE compression for bitmaps with 4 bits per pixel. The compression uses a 2-byte format consisting of a count byte followed by two word-length color indexes.

BI_BITFIELDS: The bitmap is not compressed, and the color table consists of three DWORD (defined in [MS-DTYP] section 2.2.9) color masks that specify the red, green, and blue components, respectively, of each pixel. This is valid when used with 16 and 32-bits per pixel bitmaps.

BI_JPEG: The image is a JPEG image, as specified in [JFIF]. This value SHOULD only be used in certain bitmap operations, such as JPEG pass-through. The application MUST query for the pass-through support, since not all devices support JPEG pass-through. Using non-RGB bitmaps MAY limit the portability of the metafile to other devices. For instance, display device contexts generally do not support this pass-through.

BI_PNG: The image is a PNG image, as specified in [RFC2083]. This value SHOULD only be used certain bitmap operations, such as JPEG/PNG pass-through. The application MUST query for the pass-through support, because not all devices support JPEG/PNG pass-through. Using non-RGB bitmaps MAY limit the portability of the metafile to other devices. For instance, display device contexts generally do not support this pass-through.

BI_CMYK: The image is an uncompressed CMYK format.

BI_CMYKRLE8: A CMYK format that uses RLE compression for bitmaps with 8 bits per pixel. The compression uses a 2-byte format consisting of a count byte followed by a byte containing a color index.

BI_CMYKRLE4: A CMYK format that uses RLE compression for bitmaps with 4 bits per pixel. The compression uses a 2-byte format consisting of a count byte followed by two word-length color indexes.

Note  A bottom-up bitmap can be compressed, but a top-down bitmap cannot.

See section 3.1.6 for more information on RLE compression.