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| Tag | Description |
|---|---|
| -c | Specify the compression to use for data written to the output file: none for no compression, packbits for PackBits compression, lzw for Lempel-Ziv & Welch compression, zip for Deflate compression, g3 for CCITT Group 3 (T.4) compression, and g4 for CCITT Group 4 (T.6) compression. By default tiffdither will compress data according to the value of the Compression tag found in the source file. |
| The CCITT Group 3 and Group 4 compression algorithms can only be used with bilevel data. | |
| Group 3 compression can be specified together with several T.4-specific options: 1d for 1-dimensional encoding, 2d for 2-dimensional encoding, and fill to force each encoded scanline to be zero-filled so that the terminating EOL code lies on a byte boundary. Group 3-specific options are specified by appending a ‘‘:’’-separated list to the ‘‘g3’’ option; e.g. -c g3:2d:fill to get 2D-encoded data with byte-aligned EOL codes. | |
| LZW compression can be specified together with a predictor value. A predictor value of 2 causes each scanline of the output image to undergo horizontal differencing before it is encoded; a value of 1 forces each scanline to be encoded without differencing. LZW-specific options are specified by appending a ‘‘:’’-separated list to the ‘‘lzw’’ option; e.g. -c lzw:2 for LZW compression with horizontal differencing. | |
| -f | Specify the bit fill order to use in writing output data. By default, tiffdither will create a new file with the same fill order as the original. Specifying -f lsb2msb will force data to be written with the FillOrder tag set to LSB2MSB , while -f msb2lsb will force data to be written with the FillOrder tag set to MSB2LSB . |
| -t | Set the threshold value for dithering. By default the threshold value is 128. |
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