Thank you, this was very useful.
May I ask some related questions (sorry, they may be trivial but I did not
find answers from the documentation):Since Radiance has its own RGB definition, I tried to find out what is the
RGB gamut produced by ra_tiff. Is it sRGB of something else? (pcond seems
to produce sRGB as a default - am I right?). I am using the DOS/Windows
executables. Is the resulting RGB gamut same for all systems?Regards, Markku
Unfortunately, the RGB coordinates I chose for Radiance predated (slightly) those chosen for sRGB, and they don't quite agree. In fact, the red and blue primaries are the same, only the green primary differs slightly. The gamut of the Radiance color space is therefore slightly larger than sRGB, but not significantly larger. It would be much better of course if they were the same, but it was a couple of years before I noticed the difference as sRGB came into vogue, and I didn't want to make a change that would affect the colors of all my rendered images, however slightly. If you like, you may redefine the primaries in the main src/common/color.h to match the sRGB primaries, like so:
*** color.h Wed Oct 21 17:48:07 1998
--- color_srgb.h Fri Feb 15 07:53:50 2002
···
***************
*** 60,73 ****
#define CIE_x_w 0.3333 /* use true white */
#define CIE_y_w 0.3333
#else
! #define CIE_x_r 0.640 /* nominal CRT primaries */
#define CIE_y_r 0.330
! #define CIE_x_g 0.290
#define CIE_y_g 0.600
#define CIE_x_b 0.150
#define CIE_y_b 0.060
! #define CIE_x_w 0.3333 /* use true white */
! #define CIE_y_w 0.3333
#endif
--- 60,74 ----
#define CIE_x_w 0.3333 /* use true white */
#define CIE_y_w 0.3333
#else
! #define CIE_x_r 0.640 /* sRGB primaries */
#define CIE_y_r 0.330
! #define CIE_x_g 0.300
#define CIE_y_g 0.600
#define CIE_x_b 0.150
#define CIE_y_b 0.060
! #define CIE_x_w 0.3127 /* Illuminant D65 */
! #define CIE_y_w 0.3290
!
#endif
-------------------
You'll notice above that I also use "equal energy white" for the Radiance white point, i.e., neutral. I chose this rather than the sRGB standard of D65 because it avoids the need to specify non-white sources to achieve color-balanced pictures. This is less of a problem with 3.4's incorporation of the von Kries transform, so using D65 in Radiance should work OK now so long as you render things with this in mind. Thinking about it now, I'm still a little muddy on what the exact procedure should be; I've gone so long skirting these issues in my work....
-Greg