(Batch) convert a BMP to a PNG with transparency

Question

I have +- 500 .bmp's that I would like to convert to .png's. It would be especially nice if the color white (#FFFFFF) of the original BMP's could be converted to transparent in the .png's.

PNG-8 is enough since the .bmp's are 16-colors.

I would prefer a command-line tool that I can put in a batch file, but any would be useful. Do you know of such a tool?

edit: The OS I use most is Windows 7 x64, but I also have Cygwin and various linuxes available

Answer 1

ImageMagick can do this - have a look at the Convert command, which allows you to specify a colour to be used as the transparency value:

http://www.imagemagick.org/script/convert.php

Answer 2

Using what operating system, etc ?

One suggestion - generic answer: give a try to ImageMagik.

Right from the first page you can get:

Format conversion: convert an image from one format to another (e.g. PNG to JPEG). Transparency: render portions of an image invisible.

Usage example:

convert file.jpg -transparent-color '#ffffff' file.png