R/B White Balance Settings

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umasscrew39
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R/B White Balance Settings

Post by umasscrew39 » Thu May 21, 2020 10:02 am

I've been experimenting more with the R/B white balance settings with my ZWO cameras for both live viewing and AP. For live viewing, a 50/50 balance seems to eliminate the greenish tint that many see but it is for AP that I am curious as to what is really going on. When set at 50/50 for creating the master dark and flat to use for calibration of lights in PixInsight, the captured lights will have a green background before using the Automatic Background Extractor to get the image prepared for post-processing. If left at the default 95/52 ZWO camera settings, the background in PixInsight is red prior to using the Automatic Background Extractor which is what is more expected given the experiences of others. However, my point for bringing all of this up is that I have found absolutely no difference in the final post-processing of the images as long as the same balance settings are maintained throughout the entire procedure. Am I missing something?

Menno555
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Re: R/B White Balance Settings

Post by Menno555 » Thu May 21, 2020 6:05 pm

How do you find or determine the default white balance of the Zwo?
I have the Zwo ASI385MC and thought simply that it was 50/50 but found out right away that that is not the case :p

Menno

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Re: R/B White Balance Settings

Post by admin » Thu May 21, 2020 6:57 pm

Hi Bruce,

Any effects will be subtle.

Suppose you have a 12 bit sensor in your camera so that it can produce pixel values from 0 up to 4095.

If you boost the red channel by 50% then first of all any values that were between about 2730 and 4095 will be boosted all the way up to 4095 – that implies a loss of information and may make the colours of some stars come out differently, since you'll be losing information about whether those stars were nearly saturated or really saturated in the red channel. For lower values, multiplying by 1.5 gives gaps in the data – values of 101, 102, 103, 104 will be turned into 152, 153, 155, 156 (rounding up). I don't suppose this effect would be very noticeable in a stacked image however.

Going in the other direction, reducing the value of one of the colour channels a lead to situations where that channel never fully saturates (never reaches the maximum value of 4095 even for bright stars). This can again lead to colour balancing problems. Additionally if you halve the values then values of 101, 102, 103, 104 will go to 55, 55, 56,56 - there is some loss of data here although it's probably going to be below the level of the read noise.

Cheers, Robin

umasscrew39
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Re: R/B White Balance Settings

Post by umasscrew39 » Thu May 21, 2020 8:35 pm

Hi Robin

Thanks much for the in-depth explanation and clarification. I guess this also means it is personal preference as one looks at their image and decides if they are pleased with the final results using 50/50 or 95/52 (default). An example of using the default settings for the ASI533MC Pro is Markarian's Chain which I posted in the gallery with no LP filter. To me, this color is fine but to others is probably not acceptable.

Bruce

umasscrew39
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Re: R/B White Balance Settings

Post by umasscrew39 » Thu May 21, 2020 8:38 pm

Menno

When you first plug the camera in, the default settings will appear in SharpCap. I use to have a 385 but cannot remember if the default settings for white balance are 50/50 or 95/52. I am suspecting it is 95/52 as I believe most ZWO cameras are the same but I cannot confirm that.

roelb
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Re: R/B White Balance Settings

Post by roelb » Fri May 22, 2020 12:22 am

For mine 533:
red: 52
blue: 90
Have experimented with other values of blue but wasn't satisfactory.
In general when clicking 'auto color balance' the blue color is too high and must be lowered manually.
Roel
Celestron Nexstar Evolution 8 - Celestron Nexstar 6 SE - OTA 5 SE - StarSense
Starlight Xpress Lodestar X2 Mono -- ZWO ASI290MM -- ZWO ASI224MC -- ZWO ASI533MC-Pro

Menno555
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Re: R/B White Balance Settings

Post by Menno555 » Fri May 22, 2020 7:48 am

Okay, thanks both. Will try that.

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