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One can use matlab to know the RGB values's data for all the pixels. But the camera captures the data by measuring intensities at each photodiode. These values are such that they correspond to one out of R, G, or B, depending on what bayer filter allows that particular photodiode to capture. Now these intensities are processed via demosaicing algorithms and they lead to the data that matlab shows, i.e. the RGB values at each pixel. Is it possible to trace back the intensity values from the RGB values?

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    \$\begingroup\$ I'm voting to close this question as off-topic because this is about image processing in a non-photographic context. \$\endgroup\$
    – mattdm
    Jun 19, 2016 at 17:47
  • \$\begingroup\$ No, there is not a 1-to-1 relationship between the RGBG quad of pixels and the final R,G,B values. \$\endgroup\$ Jun 20, 2016 at 11:07

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Only if you still have the original data from the raw file. You cannot normally derive the original monochromatic luminance values from each sensel (pixel well) on the sensor from the demosaiced data because there are almost always more than one set of original data that could result in the same final RGB values, just as there are more than one set of RGB values that could result from the same original raw data set (depending on the processing parameters). But even when the exact processing parameters are known, it is still usually possible for more than one original data set to result in the same processed output. There are exceptions. A totally dark image with values of (0,0,0) at every single pixel would be one such example. But practically speaking it is not possible to derive the original luminance values from normal images.

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