0 Computational photography table

Summary  of  channel  sensitivity  and  color  correction  matrices. The  balance  gains  and  the
       sensitivity gain are respectively denoted by G  G  G   and GE .
                                             1  2  3

        QE Set   Channel Response     G  G  G          GE             M
                                         1  2  3

                                                               1558  0531  0027
        RGB      2616 3972 3159     1518 1000 1257    2.616  0078     1477  0399
                                                               0039  0508    1469

                                                               2000  1373    0373
        RPB      2616  10390 3159   3972 1000 3289    1.000  1062     3384 1322
                                                               0412  1248    1836

                                                             2554     2021   1533
        CMY      5134 5486 5929     1155 1081 1000    1.752    0941  1512    1571
                                                               1201   1783  1984

reflectance,  Qi is the quantum efficiency,  and IEI is the exposure index.  The additional
values are Planck’s constant h, the speed of light c, the spectral luminous efficiency function
V ,  and  normalization  constants  arising  from  the  definition  of  exposure  index. Using  a
relative spectral power distribution of D65 for the illuminant, a pixel size of l  22  m,
and a spectrally flat 100% diffuse reflector, the mean number of photo-electrons captured
in each pixel at an exposure index of ISO 1000 are shown under “Channel Response” in
Table 1.1.


The balance gains listed are factors to equalize the color channel responses.  The sensi-
tivity gain shown is calculated to equalize the white balanced pixel values for all sets of
quantum efficiencies. The color correction matrix shown for each set of quantum efficien-
cies was computed by calculating Equation 1.5 for 64 different color patch spectra, then
finding a color correction matrix that minimized errors between color corrected camera
data and scene colorimetry, as described in Reference [68].
 
The illustration compares the noise level in images captured at the same exposure index
and corrected to pixel value P  . For a neutral, the mean of the balanced pixel values is
                               C
the same as the color corrected pixel values.  Since the raw signals are related to the bal-
anced signal by the gains shown in Table 1.1, the original signal levels can be expressed as
follows:
                                      1    0     0        
                                                        P
                                    GE G1                 C
                                                     
                                            1
                                                           
                            P         0          0      P                            (1.6)
                                                     
                             O            GE G2           C
                                      0    0     1      P
                                                          C
                                                GE G3


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