# Reflectance data

Hello, I use a device to measure the reflectance from 344 to 1045
wavelength,
How could I convert these measured data into Radiance RGB, and how could I
calculate the overall reflectance from the measurement?

I try to use weights of RGB channels in Radiance, but which wavelength out
of 344 - 1045 should I select for each channel?

Thanks,
Jia

You can use the routines defined in src/common/ccolor.h to convert from spectral measurements to a CIE color and from there to RGB:

#include "ccolor.h"
{
C_COLOR clr;
float spec_data[MYNWL];
float rgb[3];
double myLuminance = 0.5;

/* set spec_data[] array] */
c_sset(&clr, 344.0, 1045.0, spec_data, MYNWL);
ccy2rgb(&clr, myLuminance, rgb);
}

Note that you have to decide the number of wavelengths ahead of time, and they must be evenly spaced.

I've arbitrarily set the overall Y value to 0.5, but of course you set it to what you need. I can't help you with that part.

Cheers,
-Greg

···

From: Jia Hu <[email protected]>
Date: September 3, 2014 8:02:35 PM GMT+01:00

Hello, I use a device to measure the reflectance from 344 to 1045 wavelength,
How could I convert these measured data into Radiance RGB, and how could I calculate the overall reflectance from the measurement?

I try to use weights of RGB channels in Radiance, but which wavelength out of 344 - 1045 should I select for each channel?

Thanks,
Jia

Hi Jia,

I have been using mgfilt to convert from spectrally resolved reflectance to rgb.

Cheers, Lars.

···

Hello, I use a device to measure the reflectance from 344 to 1045 wavelength,
How could I convert these measured data into Radiance RGB, and how could I calculate the overall reflectance from the measurement?

I try to use weights of RGB channels in Radiance, but which wavelength out of 344 - 1045 should I select for each channel?

Thanks,
Jia