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Color Balance Setings for the ASI2600MC-Pro

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#1 Kenboy

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Posted 29 April 2021 - 10:50 PM

I have been following the threads about the correct color balance setting for the AI2600MC-Pro in ASICAP. The factory default setting is: Red=52, Blue=95. Another setting that is often cited here is R=50, B=50. To resolve the differences, I did an experiment in which I took 8-bit PNGs of a white, sunlight piece of vellum. I found that the factory setting (52R, 95B) was decidedly too blue (albeit, a very pretty blue) and that the 50/50 setting was too green. Checking the auto-white balance box gave the result 85R, 74B and a perfectly grey PNG image. Instead of two or three “humps” in the histogram, there was just one and the grid pattern disappeared. I haven’t yet tried the 85B/74B setting at night, but I suspect that it is much more balanced than the other two. Let us know what you think of the 85R/74B setting if you try it.



#2 sharkmelley

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Posted 30 April 2021 - 01:17 AM

If you use values greater than 50 then you are scaling the data upwards.  Is this done digitally i.e. do you end up with extra gaps in the histogram of values?  If so, then it is not advisable because you are no longer using the raw data from the sensor.  Instead, white balance should be performed after calibration and stacking.

 

It will be very interesting to take a look at one of your raw files using the 85B/74B setting.

 

Mark


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#3 TrustyChords

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Posted 30 April 2021 - 02:15 AM

If you use values greater than 50 then you are scaling the data upwards.  Is this done digitally i.e. do you end up with extra gaps in the histogram of values?  If so, then it is not advisable because you are no longer using the raw data from the sensor.  Instead, white balance should be performed after calibration and stacking.

 

It will be very interesting to take a look at one of your raw files using the 85B/74B setting.

 

Mark

Good question.

 

Is the raw data isomorphic digitally, between the 50/50 vs 85B/74B data, via some linear function?

 

Or is data at the higher settings potentially clipped or otherwise difficult to get back..



#4 TelescopeGreg

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Posted 30 April 2021 - 05:03 PM

To not hijack this thread, I posted another on a related topic, more focused on the tools.

 

https://www.cloudyni...-color-balance/



#5 sharkmelley

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Posted 01 May 2021 - 01:25 AM

If you use values greater than 50 then you are scaling the data upwards.  Is this done digitally i.e. do you end up with extra gaps in the histogram of values?  If so, then it is not advisable because you are no longer using the raw data from the sensor.  Instead, white balance should be performed after calibration and stacking.

 

It will be very interesting to take a look at one of your raw files using the 85B/74B setting.

I managed to find a FITS file where the Red/Blue setting was not 50R/50B  The histogram of data had varying gaps which is proof that digital scaling had been applied to the raw data.  This means the data are no longer raw because it has been manipulated.  Without going into too much technical detail, this introduces the possibility of causing coloured concentric banding in the background of your images.  

 

Always use 50R/50B to acquire data. White balance is best left as a post-processing step.

 

Mark


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#6 Kenboy

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Posted 01 May 2021 - 02:25 PM

Thanks for the insights, guys. It sounds like settings other than 50/50 can cause posterization. If anyone has the time, I have 2 questions:

 

1. Why would the software solution not do the same thing, since it will also scale the values?

 

2. Is the difference really going to be noticeable in the final image? I imagine that the effect of doing white balance in hardware is quite small.

 

(BTW, I did the test with ASICAP, not ASIStudio.)

 

Best regards.



#7 sharkmelley

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Posted 01 May 2021 - 08:59 PM

Thanks for the insights, guys. It sounds like settings other than 50/50 can cause posterization. If anyone has the time, I have 2 questions:

 

1. Why would the software solution not do the same thing, since it will also scale the values?

 

2. Is the difference really going to be noticeable in the final image? I imagine that the effect of doing white balance in hardware is quite small.

 

(BTW, I did the test with ASICAP, not ASIStudio.)

 

Best regards.

1. In software, the scaling is done in floating point arithmetic so it doesn't round/truncate the result to the nearest integer (which introduces systematic biases into the data).

 

2. The difference can certainly be noticeable in the final image. Here's an example discussion from the Sony A7S:

https://www.dpreview...s/post/59378650

 

You paid a big premium to buy a cooled colour dedicated astro-camera.  There's no sense in applying the kind of scaling that might make it perform as badly as a consumer mirrorless camera!

 

Mark


Edited by sharkmelley, 01 May 2021 - 09:07 PM.

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#8 calypsob

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Posted 06 May 2021 - 10:44 AM

Why is it so important to have white balance dialed in perfectly? You have full control in post processing. If you had an LP gradient, the data will be tinged yellow, if you had high cirrus clouds or sky glow from a darksite there will be other white balance issues to contend with.


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