PDF compressions for raster images.
Values:
| IG_PDF_COMPRESSION_NONE | 0 | No compression. |
| IG_PDF_COMPRESSION_CCITT_G3 | 1 | CCITT G3 compression. |
| IG_PDF_COMPRESSION_CCITT_G4 | 2 | CCITT G4 compression. |
| IG_PDF_COMPRESSION_CCITT_G32D | 3 | CCITT G32D compression. |
| IG_PDF_COMPRESSION_JPEG | 4 | JPEG compression. |
| IG_PDF_COMPRESSION_LZW | 5 | LZW compression. |
| IG_PDF_COMPRESSION_RLE | 6 | RLE compression. |
| IG_PDF_COMPRESSION_DEFLATE | 7 | Deflate compression. |