Recreating Spectral Response from 6-Channel Color Sensor

[AxisCat]

Hi All,

This is a project I started a couple of years ago then got stuck or bored and stopped working on it. I am thinking about picking back up where I left off. I am using a AMS AS7262 color sensor with the following overlapping channels: 450, 500, 550, 570, 600 and 650 nm, each with 40nm FWHM.

I used a Digikröm CM110 Monochromator and stepped through the spectrum in 1nm increments saving the output from the sensor to a file. My light source was a standard 100 watt halogen household bulb. This is what I measured:

The continuous dark blue curve is from a photodiode I am trying to use as a reference. I understand this is really hard stuff to do with the limited equipment I have available. Is it even possible to recreate a fairly accurate spectral response using just these 6 discrete channels? The manufacturer provides some information that eludes to it being possible.

Anyone have any thoughts?

Thanks,
Axis

 

[Andy Resnick]

Hi All,

This is a project I started a couple of years ago then got stuck or bored and stopped working on it. I am thinking about picking back up where I left off. I am using a AMS AS7262 color sensor with the following overlapping channels: 450, 500, 550, 570, 600 and 650 nm, each with 40nm FWHM.

I used a Digikröm CM110 Monochromator and stepped through the spectrum in 1nm increments saving the output from the sensor to a file. My light source was a standard 100 watt halogen household bulb. This is what I measured:
View attachment 336147
The continuous dark blue curve is from a photodiode I am trying to use as a reference. I understand this is really hard stuff to do with the limited equipment I have available. Is it even possible to recreate a fairly accurate spectral response using just these 6 discrete channels? The manufacturer provides some information that eludes to it being possible.

Anyone have any thoughts?

Thanks,
Axis

Off the top of my head, I suggest that you first normalize each channel and then assign/compute wavelengths according to ratios of the different channels- that's generally how color vision works.

 

[AxisCat]

I appreciate the reply. The "mapping function" is the part I am stuck on. Someone suggested Fourier transforms because the curves looked like filters and the math can be reversed. That looked really complicated so I haven't researched it any further. Another person's thought was using a matrix to calibrate. The input matrix would be 6x1 (sensor output x 6-channels), the correction matrix would be 6x300 (700nm - 400nm), and the output matrix would be a 1x300 representing the spectral response from 400-700nm. I really don't know which direction to take with this.

 

[hutchphd]

What does

accurate spectral response

mean to you operationally? What does accuracy mean in this context? If you desire spectral response you want to use a very high precision spectrograph.....that is what they do. Or are you trying to make specific colorimeter? I have designed each. They are different things although obviously not disjoint.
So you need to specify exactly what you wish to do.

 

[KAHR-Alpha]

Why don't you just do a least squares fit of the reference curve?

 

[sophiecentaur]

Anyone have any thoughts?

This sounds interesting.
Bearing in mind how our tristimulus colour vision can give a matching colour for many combinations of source spectra (metamers), does this six channel sensor not have the same potential problem? I can see how it will get a correct wavelength for monochromatic light but for light with multiple wavelengths, how can it resolve the individual wavelengths? Albeit with better accuracy.
What would be your application for this sensor?

 

[hutchphd]

I appreciate the reply.

So you have a camera that sees six different fundamentall "camera-colors" as defined by each of the six types of sensors.
Your eye sees three fundamental "eye-colors" for similar reasons. It constructs any color by recognizing the admixture of the three sensors.
Clearly one can create correspondences between these two systems, but there will be serious uniqueness questions for any intermapping. The physics just involves integrating each sensor sensitivity over the (object+illuminant) spectrum. This is the mathematics of color filters.