Reads a TIFF file as input. Produces a portable anymap as output. The type of the output file depends on the input file - if it's black pbm file; if it's grayscale, generates a pgm file; otherwise, a ppm'' file. The program tells you which type it is writing.
This program cannot read every possible TIFF file -- there are myriad variations of the TIFF format. However, it does understand monochrome and gray scale, RGB, RGBA (red/green/blue with alpha channel), CMYK (Cyan-Magenta-Yellow-Black ink color separation), and color palette TIFF files. An RGB file can have either single plane (interleaved) color or multiple plane format. The program reads 1-8 and 16 bit-per-sample input, the latter in either bigendian or littlendian encoding. Tiff directory information may also be either bigendian or littendian.
One reason this program isn't as general as TIFF programs often are is that it does not use the TIFFRGBAImageGet() function of the TIFF library to read TIFF files. Rather, it uses the more primitive TIFFReadScanLine() function and decodes it itself.
There is no fundamental reason that this program could not read other kinds of TIFF files; the existing limitations are mainly because no one has asked for more.
The PNM output has the same maxval as the Tiff input, except that if the Tiff input is colormapped (which implies a maxval of 65535) the PNM output has a maxval of 255. Though this may result in lost information, such input images hardly ever actually have more color resolution than a maxval of 255 provides and people often cannot deal with PNM files that have maxval have a maxval
tifftopnm creates a PGM (portable graymap) file containing the alpha channel values in the input image. If the input image doesn't contain an alpha channel, the alpha-filename file contains all zero (transparent) alpha values. If you don't specify --alphaout, tifftopnm does not generate an alpha file, and if the input image has an alpha channel, tifftopnm simply discards it.
If you specify - as the filename, tifftopnm writes the alpha output to Standard Output and discards the image.
See pnmcomp(1) for one way to use the alpha output file.
Dump TIFF file information to stderr. This information may be useful in debugging TIFF file conversion problems.