John,
I'm checking quickly with mingw g++ 3.4.5 on a PC. It does not currently compile. The results and the code I used are attached, so you can tell me if I am misusing the extension.
Thanks.
For starters there is a dependancy on another extension called 'toolbox'. You might want to remove that or somhow document that it is necessary, because it is not part of the gil distribution in boost.
You're right. I will scope it inside a compiler symbol ( ENABLE_GRAY_ALPHA ) for now. I probably need to talk to Lubomir asking him if he wants to add gray_alpha. It's a pretty straight forward change to the current lib. This reminds me that there are some other additions that should be added. Can you try to compile again? Are you planning on using the lib? Thanks a lot for your time, Christian