Mark,
You really ought to use Fireworks or ImageReady to do this kind of work… Fireworks would be my preference…
I don’t know of any tools that are open/free that will do the job… sorry.
— john 
it won’t do the conversion, but once you do have them converted to png format, pngcrush (http://pmt.sourceforge.net/pngcrush/) can be used to optimize the files.
i typically use it in conjunction with imagemagick (http://www.imagemagick.org/).
I think ImageMagick http://www.imagemagick.org/ would probably be the best tool. Or at least I *would* think so if I could get the web page to come up right now :-/
I’d suggest using two different tools for the job, since conversion and optimization are two distinctly different tasks.
The conversion from TIFF to PNG can be done with a number of different tools. My tool of choice is IrfanView (Win32, GUI, http://www.irfanview.com/ ). It won’t offer you any editing features, but it will read just about any image format out there and output PNGs.
Then there is the second part, making sure the PNGs themselves are optimized. PNGCrush (”Any” platform, Command Line, http://pmt.sourceforge.net/pngcrush/ ) is really the only tool you will ever need to consider. If you have the time, or have the power, optimizing your files with the -brute option, will create the smallest files. Often 30-40% smaller than what Photoshop is generating.
Did you try PIL? (http://www.pythonware.com/products/pil/index.htm) It might do what you want…
— Hans
I recommend pngcrush as well, for non-lossy optimization. There are times when pngquant has been useful to me as well, if you are willing to dither down to a lower color depth. For me, the most amazing aspect of pngquant (http://www.libpng.org/pub/png/apps/pngquant.html) is that it keeps alpha transparency for the lower color depth; I always thought that you had to have a 24-bit PNG to have alpha transparency.
Unfortunately, Internet Explorer does not seem to display an 8-bit PNG at all, if it has alpha transparency. It seems to work with Phoenix, which is Gecko-based, however.
Hi Mark,
I guess that John is right, Macromedia Fireworks can do the trick. I’m not sure if it has batch processing capabilities but it can handle and create png-files. There is a free demo version available on the Macromedia site.
Dieter.
— Dieter Gyselinck
Yup, Fireworks has batch-processing capabilities. Go through a little dialog box, set your options (including backups), and send it on its way. Nice and easy.
— bish
I know the problem has been solved, but just for future reference ;) I usually do these kind of things with XnView (http://www.xnview.org/) on Win32. pngcrush seems interesting though.
— Breyten
For small PNG files the most important thing to do it to get rid of unused palette entries. I forget which tools do this.
— Anonymous
I gave pngcrush a little test by running a large batch of PNGs I had created with Fireworks through its -brute option… on average I got about a 3-5% savings in file size. I suppose Fireworks has pretty good PNG support then. Therefore I’d recommend Fireworks for all your PNG needs, even though it’s expensive.
— Ben