User Manual answers my previous post about OSC narrow band "color balance" !!

[Craigar]

This seems like such a fundamental "square 1" question, but I can't find the answer.. also searched the web and really tried this was one of my search strings


"how to adjust color balance when using a dual narrow band OSC filter?" I probably can't "find a tree through the forest."


The reason I have been adjusting it is the red signal is weakest, green strongest and blue is kind of in the middle so this is how I have it set in Sharpcap Pro wanting to capture as much data as I can without clipping - (except for bright stars, can always replace those clipped stars with OSC/rgb stars in post), and I know I could lower the green more and increase the blue but afraid itmayreally "make a mess" .


Then I also wonder if I possibly should treat the flats in the same fashion, but have been adjusting the balance to get all three colors in the middle.


I'm using ngc6888 Crescent nebulae as my target

equipment: C9.25 > 3.3reducer (yields about F/3.4 at 800mm) Radian Triband filter > UV/IR cut > Qhyiii 485c uncooled 2.9um pixels

SharpCapCrescent.jpg (513.27 KiB) Viewed 2816 times

Crescent Sharpcap color balance20250706.jpg (105.14 KiB) Viewed 2816 times

[Craigar]

Thank You Robin for your patience, persistence and clear explanations

The documentation helped me better understand what the "White Balance R/G/B" really does, simplified I think it means it adjusts gain for each color, which can be a "double edged sword" and for raw images, especially for data that will be post processed it may be best left in the "neutral positions" and then adjusted with appropriate software, usually after stacking.

https://docs.sharpcap.co.uk/4.1/#!2!Image%20Controls

Here's the section that helped me with this "problem" i.e. "Should I adjust Sharpcap color balance when using a dual narrow band OSC filter?":

The Image Controls group mainly contains controls that affect the adjustments applied to the image after it has been captured by the camera sensor. Most of these adjustments are applied by adjusting the digital pixel values of the image according to some appropriate calculation. These adjustments are carried out in the camera software provided by the camera manufacturer, and are applied to the image data before the data reaches SharpCap. This means that it is very likely to be impossible to accurately undo the effects of these adjustments if you later decide that they were applied incorrectly.

For instance a control that adjusts the blue component of the image to give white balance adjustment (White Balance(B) or WBB) is likely to do so by multiplying all the pixel values for blue pixel data by some factor – perhaps 1.3 if the control is set to 130. One effect of this adjustment is that all pixel values higher than 196 will be set to the maximum pixel value of 255 (for 8 bit data). Any information in the image in that pixel range between 196 and 255 for blue pixels is lost and can never be recovered.

Given the above, you may wish to avoid using these controls, and leave them in their ‘neutral’ positions. This allows the unmodified data from the camera sensor to be received by SharpCap and saved to file. Adjustments for colour balance and other image adjustments can then be applied after processing and stacking, meaning it is always possible to go back to the original data and try again if the initial settings don’t work exactly as you had hoped. On the other hand, many people successfully produce great images by using these controls to adjust the colour balance and other aspects of the image before stacking, so both approaches are possible.

Is their a way to know (or reset) what the White Balance R/G/B neutral position was for my/any camera> The camera in question for me is a Qhyiii 485c ?

Thank You again
Craig

[admin]

Hi Craig,

glad you found what you needed in the documentation

It's difficult to know what the defaults are for a QHY camera as they tend to vary from model to model If it was a ZWO camera I could tell you straight away to set them to 50 and 50... Try opening the camera with the CTRL key pressed to stop SharpCap from loading previous camera settings and see what you get. Sadly the SDK may also try to remember settings.

There is a way to check - get a somewhat overexposed image in view, so that the histogram for all three channels reaches the right hand side. Now turn down the colour balance controls one at a time. As you turn them down , you will get to a point where the histogram for that channel finishes with a big cliff edge at 90 or 95% of the way across, instead of at the right hand side. Now, gradually turn up the colour balance until the histogram for that channel just reaches the right hand side - that should be the neutral value. Often you will find it is a 'round' number of some sort - maybe 100 or 16 or 64 or 128 (the last 3 are 'round' in computer terms - powers of 2).

Hope this helps,

Robin

[Craigar]

Thank you that method with "over exposing" sounds like a good way to proceed, BUT I would have too unscrew the Triad triband NB filter then have to retake flats, and maybe Bias/offset frames also and I'm trying for about 15hrs of good data on NGC6888 from this rig (have about 4hrs so far)and average city weather problems, so it will take about 30~40 more hours to get 10 hrs more worth of good frames - which easily could take a month cause of many cloudy nights, etc... another good reason for me to procure a "filter drawer" - that needs to be optimized for a 1.25" camera cause *I think* I read some good reasons to keep the filter close to the sensor and this filter is 1.25" mounted

[admin]

Hi,

I *think* that with bright enough illumination you should be able to determine the neutral colour balance point with the narrowband filter in place - just pick one of the channels that has a reasonable amount of bandpass in it and then go for long exposures/high gains with bright illumination to get to overexposed. Once you get the 'neutral' value for one channel, it's pretty certain that all the others will be the same.

cheers,

Robin