THE MULTISPECTRAL CAMERA TECHNIQUE

With 13 filters, the camera reflects 13 digital values for each pixel. A reflectance curve depending on the sampling interval needs to be defined on at least 41 values in the 380-780 nm interval in the visible range. Several methods may be used to create these intermediate points: direct or indirect reconstruction and interpolation.
Direct reconstruction is based on a thorough knowledge of the acquisition system, but its implementation is tricky due to the determination of the noise factor.
Indirect reconstruction – also known as acquisition reconstruction – requires the presence on the images of a standard color test chart. A transfer function between the spectra measured on the test chart and the camera’s response is generated by extrapolation.
The interpolation technique solely focuses on the camera’s response and does not require any color test chart in the image but rather a white reference. After a standardization process with this white reference standard, the camera is considered as a spectrum sampler that records a specific point of the spectral curve once every 40 nm in the visible range.
An interpolation is then required to find the missing points.