Rather than invest a significant amount of time into writing image file format readers for the myriad of different image files formats, DIRSIGreads in single file format known as PGM. Although the format of these files will be summarized here, tools for converting image files from other formats to PGM can acquired by down-loading the NetPBM distribution from the following site:
ftp://wuarchive.wustl.edu/graphics/graphics/packages/NetPBM
The PGM file format supports both and binary formatted data, however,
the format is suggested for cross-platform compatibility.
The PGM image file contains a simple three line header that indicates
the format and dimensions of the image data.
| P2 | The PGM image format marker |
| 512 512 | The X (column) and Y (row) size of the image |
| 255 | The maximum possible digital count of the pixel data |
P2
4 4
255
0 0 0 0
85 85 85 85
170 170 170 170
255 255 255 255
To utilize binary image data, the header remains in format, however, the
first line changes:
P5
4 4
255
[8-bit binary data begins here but cannot be depicted in this manual]
The NetPBM distribution comes with programs and man pages for converting from various image formats to monochrome, grey scale, and color) images. If the NetPBM tools are available on your system, a TIFF format image can be converted to a PGM binary image using the following command line:
prompt> tifftopnm < example.tif > example.pgm
To create a raw PGM instead, use the following command line:
prompt> tifftopnm < example.tif | pnmtoraw > example.pgm