Identifies the different format compression schemes.
Values:
| IG_COMPRESSION_NONE | No compression. |
| IG_COMPRESSION_PACKED_BITS | Packed bits compression. |
| IG_COMPRESSION_HUFFMAN | Huffman encoding. |
| IG_COMPRESSION_CCITT_G3 | CCITT Group 3. |
| IG_COMPRESSION_CCITT_G4 | CCITT Group 4. |
| IG_COMPRESSION_CCITT_G32D | CCITT Group 3 2D. |
| IG_COMPRESSION_JPEG | JPEG compression. |
| IG_COMPRESSION_RLE | Run length encoding. |
| IG_COMPRESSION_LZW | LZW compression. |
| IG_COMPRESSION_ABIC_BW | IBM ABIC compression. |
| IG_COMPRESSION_ABIC_GRAY | IBM ABIC compression. |
| IG_COMPRESSION_JBIG | IBM JBIG compression. |
| IG_COMPRESSION_FPX_SINCOLOR | Single color compression. |
| IG_COMPRESSION_FPX_NOCHANGE | Save with the same compression as loaded. |
| IG_COMPRESSION_DEFLATE | Deflate compression. |
| IG_COMPRESSION_IBM_MMR | IBM MMR compression. |
| IG_COMPRESSION_ABIC | IBM ABIC compression. |
| IG_COMPRESSION_PROGRESSIVE | Progressive compression (Progressive JPEG and may be PNG in future). |
| IG_COMPRESSION_EQPC | PowerSDK EQPC(Wavelet) compression. |
| IG_COMPRESSION_JBIG2 | Reserved for future use. |
| IG_COMPRESSION_LURAWAVE | This value has been deprecated and will be removed from the public API in a future release. |
| IG_COMPRESSION_LURADOC | This value has been deprecated and will be removed from the public API in a future release. |
| IG_COMPRESSION_LURAJP2 | This value has been deprecated and will be removed from the public API in a future release. |
| IG_COMPRESSION_ASCII | Image data is converted to ASCII text. |
| IG_COMPRESSION_RAW | Image data is stored directory in binary raw format. |
| IG_COMPRESSION_JPEG2K | JPEG2K compression. |
| IG_COMPRESSION_HDP | HD Photo compression. |