That depends on what the printer is expecting. But generally printers expect things in sRGB color space, same as your screen, same as your digital camera produces. In other words, if a photo doesn't print to your satisfaction, then a GC'd render in sRGB space will not print well either. If a photo does print well, then a GC'd render should print well.

Converting a color image to grayscale is another topic with its own complications. There are many ways to do the conversion. Two are most common. The first is to pick the brightest value amongst R, G, and B as the grayscale luminance. The other is to calculated a weighted sum of R, G, and B. The latter is how black-and-white TV worked. The factors in B&W TV are:

.3 * R + .59 * G + .11 * B

I'm not sure which techniques PS7 implements.

Here's a nice little page on the topic with respect to the program "the GIMP":

http://gimp-savvy.com/BOOK/index.html?node54.html

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)