I just did an avi render with the BW button set, but it didn't save black and white but color.
And it made me wonder. When I do the same with just a jpg... it saves grayscale but it still renders color.
Would it not be handy to make that button also switch rendering to black and white, not only the way an image is saved? That would save on render time considerably no? And since I do a lot of black and white... well... seems logical.
You'd loose quality a lot by working in BW directly. Think of transparencies and how they affect colors. Especially since BW isn't done by just average the RGB components.
Life is what happens to you when you're busy making other plans.
- John Lennon
I think this is a file ouput issue - not rendertime (tho it could speed up things there too)
It would be nice that the image formats blender outputs to could be saved in black and while, PNG and TGA both support Greyscale with Alpha channels to transperency is not an issue.