What do the red, blue and green sliders technically do?

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eseavey
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What do the red, blue and green sliders technically do?

Post by eseavey » Sun Jan 28, 2018 1:53 am

I have been wondering that these sliders actually do during an imaging session. I know they are for balancing color. Are these gain sliders for the individual colors? From my understanding, the gain slider actually changes the multiplication of charge into ADUs. On a 12-bit sensor this range is between 1 and 4096. So let's say the green channel has some pixels saturated where the sensor reads a value of 4096. If these color sliders would simply multiply that value, then lowering the green slider would reduce the maximum value in the histogram. I am however not seeing this happen in my tests, so I am assuming something else is happening. Does the 4096 value not correspond to the full well at unity gain? I am deciding whether it is good practice to adjust these sliders when using a color camera, or to adjust the color balance during processing.

Any insight to this is a great help,

Thanks,
Eric

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Re: What do the red, blue and green sliders technically do?

Post by admin » Sun Jan 28, 2018 9:38 am

Hi Eric,

they are a gain applied to each channel, but the gain only affects

* The displayed image
* Saved files when choosing 'save as seen'
* The mini histogram in the controls panel

Additionally, the slider value is between -100 and +100. The actual multiplication factor is given by

e^(value/100)

so ranges between 0.367 at -100, and 2.72 at +100 (1.00 at 0). I might change this to a dB gain to be a bit more logical.

cheers,

Robin

eseavey
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Re: What do the red, blue and green sliders technically do?

Post by eseavey » Wed Feb 14, 2018 12:47 am

Thanks Robin,
That was very helpful. I guessed it was a software/digital gain of sorts.
I agree that changing it to a dB gain would be more intuitive.

Thanks.

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Re: What do the red, blue and green sliders technically do?

Post by admin » Wed Feb 14, 2018 3:51 pm

Hi,

yes, I actually did the dB change as it was easy - the range is now +/- 20dB, although I suspect the center part of the range will be the most useful.

cheers,

Robin

eseavey
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Re: What do the red, blue and green sliders technically do?

Post by eseavey » Mon Sep 03, 2018 10:56 pm

Robin,
I am still a little confused, since the sliders go from 1 to 255, with 128 being center. How does this translate to the 20dB scale?

Eric

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Re: What do the red, blue and green sliders technically do?

Post by admin » Tue Sep 04, 2018 6:42 am

Ah, I think we are talking at cross purposes, sorry.

I was describing the colour sliders in live stacking. I think you were actually asking about the colour sliders in the camera control panel?

If that is correct, then your question is a bit difficult to answer, since what those controls do depends on what type of camera you are using (for instance ZWO might deal with colour balance differently to QHY, etc). I would say that in most cases the colour control sliders will effectively be an additional gain applied to each colour channel, though how the value of the slider gets converted to a gain and whether that gain is an analogue one or a digital one I really don't know, since the camera manufacturers dont publish that information.

You may be able to find out more by asking on the forums or support site for your model of camera?

cheers,

Robin

eseavey
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Re: What do the red, blue and green sliders technically do?

Post by eseavey » Tue Sep 04, 2018 8:21 pm

Thanks Robin,
I guess the answer doesn't really matter too much perhaps. When I use the smart brain to determine optimal exposure, I assume it bases it on the color slider settings right? I have mine set to R/G/B = 80/70/130 where I get a good color balance with my QHY224C. When doing the sensor analysis, you actually see 3 peaks in the histogram corresponding to each of the colors. Based on my recent images, I think I have am pretty close to finding the optimum settings for my camera. I guess I'm now splitting hairs now. :D

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