Tiff2png

The corresponding special-purpose conversion program for TIFF images was written by Willem van Schaik and is called, predictably, Tiff2png. By a strange coincidence, its latest version is also 0.6, but the program is perhaps slightly less robust than gif2png. This is primarily due to the fact that the TIFF format is hugely complex, supporting multiple forms of text annotations, both gamma and color correction, several flavors of transparency, many different sample depths, and numerous other options that might conceivably be carried over into a PNG image with a little effort (or, more likely, a lot of it).

Tiff2png's main features as a conversion program are its support for TIFF sample depths up to 16 bits and its support for transparency and alpha channels. Unlike gif2png, Tiff2png requires an explicit output filename and is therefore somewhat less convenient for batch conversions:

tiff2png foo.tiff foo.png

It is also completely quiet by default, although it supports a -v option to turn on its verbose mode:

tiff2png -v foo.tiff foo.png

Tiff2png: foo.tiff
TIFF Directory at offset 0x10008
  Image Width: 128 Image Length: 128
  Resolution: 72, 72 pixels/inch
  Bits/Sample: 8
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Extra Samples: 1<assoc-alpha>
  Samples/Pixel: 4
  Rows/Strip: 16
  Planar Configuration: single image plane
Tiff2png: 128x128x32 image
Tiff2png: 8 bits/sample, 4 samples/pixel
Tiff2png: maxval=255
Tiff2png: color-type = truecolor + alpha
Tiff2png: bit-depth = 8

Unfortunately, Tiff2png does not distinguish between associated (premultiplied) alpha and unassociated alpha. The latter is the only form supported by PNG, but Tiff2png will happily store an associated alpha channel without conversion, as in the previous example.

The program also appears not to handle Intel-format (``little-endian'': see the section entitled "Implementation" in Chapter 7, "History of the Portable Network Graphics Format") TIFF images with 16-bit samples correctly, instead storing the samples as is--which effectively means they are inverted, given that PNG samples must be stored in ``big-endian'' format. But lacking any such sample images, I was unable to verify this.

At any rate, Tiff2png is capable of converting at least some TIFF images with alpha transparency correctly, which gives it an advantage over the current NetPBM suite and pnmtopng. Although TIFF is subject to the same LZW licensing issues GIF is, it supports several other compression methods (including no compression) and is therefore less of a problem for program authors. In Tiff2png's case, all TIFF manipulations are handled via Sam Leffler's free libtiff library, which means Tiff2png itself can be updated at will without worrying about the sorts of legal issues that plagued gif2png. Source code for Tiff2png can be found on the PNG home site, http://www.libpng.org/pub/png/apps/tiff2png.html, but there are presently no prebuilt executables.