QHY183C
7
The reason is that the Color balance is a ratio of the RGB sensitivity difference. So we use a ratio
to multiply the RGB value and get it done. But if there is a bias exist. The ratio will not be correct.
For example, the G sensitivity is the double of R sensitivity.
G=2R In order to get white balance. We multiply a ratio of 2 to R
R'=2R= G so we get R=G
When a bias exist. The bias is a constant added to each pixel. So the image you see is:
R''=R + bias
G' '= G + bias = 2R+bias
Now the ratio R'': G''= (R+bias) / (2R+bias) and it is not equal to 1:2. It shows the bias will affect
the true value of the R:G. And the ratio of R:G will vary when the image light changed. It is hard
to correct with a fixed ratio.
But for DSO capture, you should keep the offset above zero and avoid the background being cut
off. A background from 1000-5000 is a good value (16bit mode) for DSO imaging.
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