mike@BRL.MIL (Mike Muuss) (02/26/89)
A few weeks ago, I was shown the program /usr/sbin/gamma, which can be used (at least on the GT and Personal Iris machines) to set a gamma correction factor for the overall screen output of the Iris. It is downstream from the regular 12-->24 bit color map, and is downstream of the screen pixels in RGB mode. I suspect that this gamma correction factor is being applied very close to the DACs, at the nether end of the Graphics Pipeline. The default gamma that is applied is 2.4 Imagine my consternation when I got my GTX machine and looked at a few already gamma-corrected images on it -- they were much too bright, and looked washed out. For a variety of reasons, I would like to be able to use this capability from some of my own programs. It does not seem to be documented in the places I looked online, I didn't mount a big search through the printed manuals, so I run the risk of looking foolish when someone says RTFM, page 42. So be it. On the assumption that /usr/sbin/gamma and the mechanism it exploits are *not* documented, I went hunting, and discovered some things: There is VERY INTERESTING system call named "sgigsc()", to exploit SGI graphics sys-calls. One of the undocumented functions that this system call implements is suspiciously named SGGR1_GAMMARAMP in <sys/sgigsc.h>. I may try a few experiments to try to figure it out; in the meantime, I certainly would appreciate it if someone could send me a code fragment to load Gamma ramps that are non-standard. Thanks! -Mike