Quote:
Originally Posted by RickS
Collecting more blue photons improves the SNR of your blue master but doesn't necessarily make the overall image more blue. It may tempt you to make it bluer, of course.
Ideally, you'll be using some form of colour calibration to determine the R:G:B ratios. There are many ways to do this and some even have a roughly scientific basis, e.g. G2V calibration or eXcalibrator.
Unfortunately, the filters and sensor characteristics aren't the only factor in play here. Atmospheric conditions, especially extinction, play a significant role as well. Having filters which flatten the response of the sensor wouldn't remove the need to do colour calibration.
Cheers,
Rick.
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agreed, the spectral sensitivity of the CCD has no direct effect after colour calibration. However, if the SNR in the blue channel is poor, there is a good reason for winding the blue contribution down - lots of images on the web have distinct "minus blue" appearances, presumably because that way of processing has yielded a smoother and more detailed looking result (a couple of images of this galaxy look quite red overall). The other area where system spectral response makes a difference is where colour balancing is carried out on an RGB and this is then overlaid with a Lum channel. If the system has low blue sensitivity, the Lum will show reduced brightness in predominantly blue areas and that will not be compensated for by the colour calibration - low blue sensitivity in Lum will show up as reduced blue in the final result. Come to think of it, this is a bit of a worry, since the recommended PI LRGB process relies on colour calibration only on the RGB...maybe that needs a rethink.
I understand that Peter used automatic colour balancing and got the result he posted - he has resisted the urge to make it look more like other images, so it looks quite blue
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I guess that, along with atmospheric extinction, galactic extinction/dust can have an effect as well. Then if you balance on the galaxy, the stars will be wrong (and vice versa).
Regards Ray