• Create Account

### #ActualBacterius

Posted 20 September 2012 - 02:01 AM

Ok, thanks everyone for your help
I have a couple final questions. I've done good progress on the path tracer and I'm now at the stage where each of my pixels in my final image have a spectral power distribution, which is basically a list of sampled wavelengths along with their respective radiance. I can convert this distribution to a color (but not a shade) easily, however I am a little confused on how to calculate the shade. Can I use the raw per-pixel radiance as luminance in my tone-mapper and scale the final RGB values by the radiance scaling factor, or should I first convert all my CIE colors to RGB, multiply them by their radiance, and tonemap that?

Basically I feel I should be able to do better than the CIE luminance approximation given that I already have the true radiance value for each per-pixel, but I am unsure if they are the same thing.

### #3Bacterius

Posted 20 September 2012 - 02:01 AM

Ok, thanks everyone for your help
I have a couple final questions. I've done good progress on the path tracer and I'm now at the stage where each of my pixels in my final image have a spectral power distribution, which is basically a list of sampled wavelengths along with their respective radiance. I can convert this distribution to a color (but not a shade) easily, however I am a little confused on how to calculate the shade. Can I use the raw per-pixel radiance as luminance in my tone-mapper and scale the final RGB values by the radiance scaling factor, or should I first convert all my CIE colors to RGB, multiply them by their radiance, and tonemap that?

Basically I feel I should be able to do better than the CIE luminance approximation given that I already have the true radiance value for each per-pixel, but I am unsure if they are the same thing.

EDIT: scaling the RGB values with the total measured radiance and tonemapping that seems to be the right thing to do, anything else produces garbage. For future reference, since I had a hard time "getting it": the absolute per-wavelength radiance in your spectral power distribution is irrelevant in determining the resulting perceived color - all that matters is the relative radiance between wavelengths (the "shape" of the distribution). However, this will only give you the color, which is fundamentally different from what you would think a "color" is because it does not encode luminance information at all - the luminance (shade) is the area under the spectral power curve (e.g. the total radiance over the visible spectrum) and this is where the absolute measurements are used. This will give you a wide luminance range to work with, which you can then tone map at your leisure.

### #2Bacterius

Posted 19 September 2012 - 02:14 PM

Ok, thanks everyone for your help
I have a couple final questions. I've done good progress on the path tracer and I'm now at the stage where each of my pixels in my final image have a spectral power distribution, which is basically a list of sampled wavelengths along with their respective radiance. I can convert this distribution to a color (but not a shade) easily, however I am a little confused on how to calculate the shade. Can I use the raw per-pixel radiance as luminance in my tone-mapper and scale the final RGB values by the radiance scaling factor, or should I first convert all my CIE colors to RGB, multiply them by their radiance, and tonemap that?

Basically I feel I should be able to do better than the CIE luminance approximation given that I already have the true radiance value for each per-pixel, but I am unsure if they are the same thing.

### #1Bacterius

Posted 19 September 2012 - 02:11 PM

Ok, thanks everyone for your help
I have a couple final questions. I've done good progress on the path tracer and I'm now at the stage where each of my pixels in my final image have a spectral power distribution, which is basically a list of sampled wavelengths along with their respective radiance. I can convert this distribution to a color (but not a shade) easily, however I am a little confused on how to calculate the shade. Can I use the raw per-pixel radiance as luminance in my tone-mapper and scale the final RGB values by the radiance scaling factor, or should I first convert all my CIE colors to RGB, multiply them by their radiance, and tonemap that?

PARTNERS