This page contains utilities.

Making bitmaps transparent

Cu_alpha is a very small and simple utility for creating transparent bitmaps.

What it does

Cu_alpha makes one color of a bitmap transparent. Being a bit more precise: ca_alpha eats all .tif and .bmp files from a directory and writes .png files in a lossless way into another directory with either black or white as transparent alpha channel.


Ortho rectified images contain empty parts you don't want to see in your CAD program, so you make these parts transparent. Other uses: Make logo's transparent for web use. Make scanned black and white drawings transparent. Etcetera.


The program is nothing more than a batch file named cu_alpha.bat. It is used to generate some input panels and to tell a program convert.exe what to do. The batch file relies on two programs: "ImageMagick" and "The Wizard's Apprentice". Credits go to these projects, url's: http://www.imagemagick.org/ and http://wizapp.sourceforge.net/.


Only a Windows version. If source files share the same name with a different extension, only .bmp will be processed. abc.tif and abc.bmp will be transformed to abc.png where abc.tif is ignored.


  • No installer, download cu_alpha.zip

  • Unzip (for example to c:\bin\)
  • Make a desktop shortcut to cu_alpha.bat (right click on Desktop, etc.)
  • Optionally Ctrl+drag the shortcut to your start menu button.

All files

See Downloads for the zip file.

This site is hosted by StringIT.

Information and software on this site is offered -as is- without any warranty and licensed in different ways. You should read the page about licensing before use.