- #1
maka89
- 68
- 4
Hi. I am working on a linear algebra problem that arose somewhat like this: Suppose that you are shining a light with a known intensity spectrum [itex]P(\lambda)[/itex] upon a surface with an unknown reflection spectrum, [itex]R(\lambda)[/itex]. You have a detector to detect the total reflected light intensity, I. How to find [itex] R(\lambda)[/itex] ?
We know that:
[itex] I = \int_{400}^{800} P(\lambda)R(\lambda) d\lambda \approx \Delta\lambda\sum_{i=1}^N P(\lambda_i)R(\lambda_i)[/itex].
My strategy so far has been:
Rewrite to [itex]I \approx \vec{A^T} \cdot \vec{R}(\vec{\lambda})[/itex], where [itex] \vec{\lambda^T} = [\lambda_1, \lambda_2, ..., \lambda_N][/itex], [itex]\vec{R}(\lambda) = [R(\lambda_1), R(\lambda_2),...] [/itex]and [itex] \vec{A^T} = \Delta\lambda[P(\lambda_1), P(\lambda_2),...][/itex].
To be able to solve(or rather approximate) the spectrum i figured I need to have at least N intensity measurements with different light sources so that i don't have an underdetermined system.
Then one gets a linear system where row k is:
[itex]\vec{I} \approx A \vec{R}(\vec{\lambda})[/itex]. Where row k of A is: [itex] A_k = \Delta\lambda[P_k(\lambda_1), P_k(\lambda_2),...][/itex].
Then I figured to find the least square solution of the linear system.
This yielded poor results so far, but that may be to bugs in the code or poor choice of lightsource spectrum.
Is my approach reasonable? How do I choose[itex] P_k(\lambda)[/itex](This is so far a theoretical probelm, so I can choose them to whatever i want)?
Does anyone know of a similar problem that I can learn from?
We know that:
[itex] I = \int_{400}^{800} P(\lambda)R(\lambda) d\lambda \approx \Delta\lambda\sum_{i=1}^N P(\lambda_i)R(\lambda_i)[/itex].
My strategy so far has been:
Rewrite to [itex]I \approx \vec{A^T} \cdot \vec{R}(\vec{\lambda})[/itex], where [itex] \vec{\lambda^T} = [\lambda_1, \lambda_2, ..., \lambda_N][/itex], [itex]\vec{R}(\lambda) = [R(\lambda_1), R(\lambda_2),...] [/itex]and [itex] \vec{A^T} = \Delta\lambda[P(\lambda_1), P(\lambda_2),...][/itex].
To be able to solve(or rather approximate) the spectrum i figured I need to have at least N intensity measurements with different light sources so that i don't have an underdetermined system.
Then one gets a linear system where row k is:
[itex]\vec{I} \approx A \vec{R}(\vec{\lambda})[/itex]. Where row k of A is: [itex] A_k = \Delta\lambda[P_k(\lambda_1), P_k(\lambda_2),...][/itex].
Then I figured to find the least square solution of the linear system.
This yielded poor results so far, but that may be to bugs in the code or poor choice of lightsource spectrum.
Is my approach reasonable? How do I choose[itex] P_k(\lambda)[/itex](This is so far a theoretical probelm, so I can choose them to whatever i want)?
Does anyone know of a similar problem that I can learn from?