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How to increase color depth in the dark or bright ranges?

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#1 Marcin1960

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Posted 14 June 2021 - 03:33 AM

In some cases, if I make exposure longer (or increase gain) to resolve dark areas, I get  other areas overexposed.

 

And reverse is true (if bright areas are resolved, darker areas get too dark, without details).

 

Is there a way in SharpCap (or FireCapture) to mitigate this problem?



#2 HasAnyoneSeenMyNebula

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Posted 14 June 2021 - 03:07 PM

I am too new to comment from an astroimaging perspective. I can say that from a terrestrial photography perspective you are better off not blowing out the highlights as the shaddows are easier to correct.

 

Here is a thought...you could try two stacks---one to expose for the darks, and one to expose for the lights. Then merge them. I have not done this yet myself but I know it can be done.



#3 Marcin1960

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Posted 14 June 2021 - 04:48 PM

Here is a thought...you could try two stacks---one to expose for the darks, and one to expose for the lights. Then merge them. I have not done this yet myself but I know it can be done.

 

Yes, I did something like that. I just changed the exposure/gain during the capture. It was a little messy.

 

But I am looking for more elegant solution. There are so many interesting functions in SharpCap and FireCapture. Any other idea, anyone?



#4 dcaponeii

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Posted 14 June 2021 - 05:37 PM

Using curves in post processing is pretty effective at this I think.



#5 Lacaille

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Posted 14 June 2021 - 10:19 PM

Using curves in post processing is pretty effective at this I think.


I agree. Don’t overexpose your video capture (keep the histogram at about 70% - have a look at the recent thread here on CN discussing histogram settings).

Then take the stacked and sharpened image into Photoshop or GIMP and open the image in the “Curves” interface. Try pulling the curve into different shapes and look at the effect. Lifting the left edge should brighten the dark areas while leaving the bright areas as they are.

Mark

#6 Tom Glenn

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Posted 15 June 2021 - 02:35 AM

It would be helpful if the OP would elaborate on what he is imaging.  From other threads, I know he is using planetary imaging techniques but on terrestrial landscape objects.  Whatever the target, if you want to capture only a single exposure, then you have to protect the highlights, and then push the shadows in processing with curves.  Stacking many frames makes this possible by increasing bit depth, but there are always limitations on what can be achieved in a single exposure, depending on the nature of the target.  



#7 Marcin1960

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Posted 15 June 2021 - 02:57 AM

It would be helpful if the OP would elaborate on what he is imaging.  From other threads, I know he is using planetary imaging techniques but on terrestrial landscape objects.

 

Not exactly. My question is of general nature, and I do not want to limit it to specific situations.

 

But if you want my question to be more specific, I will try.

 

I am curious if it is possible with capturing software, to increase the depth on both ends, dark and light at the same time. "Curious" is the key word, as it is fun for me to explore such things.

 

Whether it will be useful for a particular area of imaging, at this moment is secondary. (I will look at that when I am out my light polluted city, right now I want to get better command of hardware and software)



#8 happylimpet

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Posted 15 June 2021 - 03:11 AM

If you're exposing for the highlights, your capture parameters wont be ideal for the fainter areas. But having said that, they wont be THAT inappropriate. If you were exposing purely for the darker areas you'd possibly have longer exposures for each frame, and higher gain, but the result is unlikely to be hugely better.

 

If the darker areas dont have enough data you just need longer overall exposures - maybe combine multiple runs (in winjupos, if doing planetary).



#9 Tom Glenn

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Posted 15 June 2021 - 03:28 AM

I am curious if it is possible with capturing software, to increase the depth on both ends, dark and light at the same time. 

 

No, what you are describing cannot be done with software, because the dynamic range of the sensor is a property of the sensor itself.  There is a fixed number of electrons available in each photo site, and once they are saturated, you lose all additional information.  So, you have to stay below 100% saturation if you are concerned about every highlight.  If the scene has extreme dynamic range, you will lose information in the shadows by recording for the highlights, but you can regain some of it by nonlinear curves adjustments on a deep stack.  But, if shadow detail is what you are really interested in, then you would need to expose for those, and lose the highlights.  Examples would be trying to image both the sunlit and night sides of the Moon at the same time.  You cannot maximize details on both in one exposure.  



#10 Marcin1960

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Posted 15 June 2021 - 03:30 AM

 

If the darker areas dont have enough data you just need longer overall exposures - maybe combine multiple runs (in winjupos, if doing planetary).

 

In winjupos? Could you elaborate, please?



#11 Marcin1960

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Posted 15 June 2021 - 03:41 AM

 Examples would be trying to image both the sunlit and night sides of the Moon at the same time.  You cannot maximize details on both in one exposure.  

 

I know. But I am looking for a trick to do just that ;)

 

Perhaps manual changing of gain/exposure parameters during the capture? How to process it later?



#12 happylimpet

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Posted 15 June 2021 - 03:55 AM

If the scene has extreme dynamic range, you will lose information in the shadows by recording for the highlights, but you can regain some of it by nonlinear curves adjustments on a deep stack.  But, if shadow detail is what you are really interested in, then you would need to expose for those, and lose the highlights.   

I agree, but aside from extreme examples like this, mostly you just need longer exposures overall (ie more data, more scope time) to get deeper, and the finessing of capture parameters will not be the biggest factor. It will help obviously and is well worth getting right but you need both.

 

In winjupos? Could you elaborate, please?

WinJupos allows long series' of planetary images to be combined without smearing due to planetary rotation. Its a specific case that allows for getting much deeper, high SNR results without sacrificing detail.



#13 dcaponeii

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Posted 15 June 2021 - 08:09 AM

Using the Moon as an example it should be possible to duplicate a layer and then process one layer for the shadows and the other layer for the highlights and then merge the layers appropriately (perhaps by removing the offending highlight areas for the layer processed for shadows.  I've had a little success with this but it's a chore to keep the boundary between the dark and light areas from developing artifacts.  I'm sure there are others with much better abilities in post processing that could elaborate.  Even merging two separate captures, one optimized for shadow areas and the other for the highlights should be possible.  I'm thinking the Moon here but in principle it should work for any application.



#14 KpS

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Posted 15 June 2021 - 09:38 AM

When shooting, you can not only select the exposure and gain, but you can also change the gamma setting. However, this is generally not recommended. Increasing gamma value brighten dark areas at the expense of the slope in bright parts thus reducing their contrast.



#15 Marcin1960

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Posted 16 June 2021 - 03:15 AM

There is a fixed number of electrons available in each photo site, and once they are saturated, you lose all additional information.  So, you have to stay below 100% saturation if you are concerned about every highlight.  If the scene has extreme dynamic range, you will lose information in the shadows by recording for the highlights, but you can regain some of it by nonlinear curves adjustments on a deep stack.  But, if shadow detail is what you are really interested in, then you would need to expose for those, and lose the highlights.  Examples would be trying to image both the sunlit and night sides of the Moon at the same time.  You cannot maximize details on both in one exposure.  

 

I wonder what will happen if I use binning (2x) and Barlow (2x) at the same time? smile.gif

 

Can I utilize the fact that info comes from four pixels?


Edited by Marcin1960, 16 June 2021 - 11:49 AM.



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