Brightness and White Balance Adjustments after Smart Histogram Brain
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Brightness and White Balance Adjustments after Smart Histogram Brain
I want to make sure that I'm clear on the process steps for setting all of the various components for good exposure and if I'm doing it the best way:
1) After completing the sensor analysis, I will use the Smart HIstogram Brain function to see the set of recommended gains and exposures. Let suppose I select an exposure time of 50 seconds and the associated gain.
2) Following this, I assume that I need to set the Brightness (ZWO ASI294MC). How do I determine the best brightness level to select? Is it just a visual adjustment to what appears best? Should the background be pretty dark? Should I be trying to achieve a certain histogram shape? Also, I have to wait for 50 seconds to the result of each change on the histogram, correct? Is there a better way?
3) Following this, I assume that I need to set the Red and Blue white balance sliders. Again, I have to wait 50 seconds to see the result of each change. Is there a better way?
Thanks!!
Mark
1) After completing the sensor analysis, I will use the Smart HIstogram Brain function to see the set of recommended gains and exposures. Let suppose I select an exposure time of 50 seconds and the associated gain.
2) Following this, I assume that I need to set the Brightness (ZWO ASI294MC). How do I determine the best brightness level to select? Is it just a visual adjustment to what appears best? Should the background be pretty dark? Should I be trying to achieve a certain histogram shape? Also, I have to wait for 50 seconds to the result of each change on the histogram, correct? Is there a better way?
3) Following this, I assume that I need to set the Red and Blue white balance sliders. Again, I have to wait 50 seconds to see the result of each change. Is there a better way?
Thanks!!
Mark
Re: Brightness and White Balance Adjustments after Smart Histogram Brain
Hi Mark,
Have you checked out the Histogram documentation from the Sharpcap manual yet? This should tell you what you need to know.
https://docs.sharpcap.co.uk/3.2/#Using% ... %20Quality
Heather
Have you checked out the Histogram documentation from the Sharpcap manual yet? This should tell you what you need to know.
https://docs.sharpcap.co.uk/3.2/#Using% ... %20Quality
Heather
Re: Brightness and White Balance Adjustments after Smart Histogram Brain
Mark
It should make sense if you look at the images.
Dave
Brightness is ZWOspeak for offset. Have a read of this thread viewtopic.php?f=9&t=1209&start=20 around Oct 16. Create a bias frame which has a balanced histogram in FITS Liberator. For a given gain, set the exposure to the minimum possible and capture a single frame with the camera cap on (a zero exposure dark frame). Keep adjusting brightness until the FITS Liberator histogram is centralised. That is the brightness to use for that particular gain setting. Change the gain and you need to re-establish the offset (brightness) value.How do I determine the best brightness level to select
It should make sense if you look at the images.
Dave
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Re: Brightness and White Balance Adjustments after Smart Histogram Brain
Thanks Dave! I've read through that thread a couple of times and understand that I should use the Offset (Brightness) that provided a centralized histogram of the bias frame at a selected gain. I'm uncertain as to Brian's suggestion to use the "minimum offset". How is that minimum determined?
Re: Brightness and White Balance Adjustments after Smart Histogram Brain
Mark
I am sure Brian will be along soon to enlighten you.
Dave
I am sure Brian will be along soon to enlighten you.
Dave
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Re: Brightness and White Balance Adjustments after Smart Histogram Brain
Hi,
The brain algorithm wants to separate the histogram from the left-hand side. Often it doesn't need to add any offset to do that because the sky brightness is sufficient. When that happens it will suggest minimum offset but you can always go a little higher.
Cheers, Robin
The brain algorithm wants to separate the histogram from the left-hand side. Often it doesn't need to add any offset to do that because the sky brightness is sufficient. When that happens it will suggest minimum offset but you can always go a little higher.
Cheers, Robin
Re: Brightness and White Balance Adjustments after Smart Histogram Brain
I agree wholeheartedly that sky brightness contributes mightily to shifting the histogram rightward but the problem is with the darks not the lights. In my experience the Brain recommends relatively short exposures even though my skies are darker than average but so be it. With an uncooled camera like mine in the dead of winter a short exposure results in a clipped histogram (see attachment). During calibration this "missing energy" wreaks havoc especially when stretching the image to eke out faint nebulosity. My apologies if the Brain's algorithm has been improved since then. I haven't used it since that time. Now I advocate the approach I learned in the AAVSO CCD Photometry class which uses Bias frames to determine the proper Offset.
Brian
Brian
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Re: Brightness and White Balance Adjustments after Smart Histogram Brain
I performed the bias test on my ZWO ASI294 MC and yielded the following data. SharpCap offers a gain setting from 0-570 and brightness settings from 0-80. Does this look reasonable? I also noted that a couple of the gain settings produced bimodal histograms. Why would this be?
Gain Brightness
100 10
150 15
200 18
250 18
275 20
300 25
325 35
350 45
375 50
400 60
425 75
450 80
Thanks,
Mark
Gain Brightness
100 10
150 15
200 18
250 18
275 20
300 25
325 35
350 45
375 50
400 60
425 75
450 80
Thanks,
Mark
Re: Brightness and White Balance Adjustments after Smart Histogram Brain
Mark
Can you post a couple of example FITS Liberator images as above. Also an example of a bimodal one - I might have seen that before, I will have a hunt round in my old data. What colour space is being used?
Dave
Can you post a couple of example FITS Liberator images as above. Also an example of a bimodal one - I might have seen that before, I will have a hunt round in my old data. What colour space is being used?
Dave
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