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Does NB combine with RGB add to total integration

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#1 Peregrinatum

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Posted 14 May 2021 - 10:54 AM

I'm on a project right now where I want to add some NB to my RGB, it got me thinking if the NB adds to the total integration time or not?

 

For example, say I want to blend a 5 hr Ha integration to a 5 hr R integration, seems like all I am doing is either averaging pixels or replacing pixels based on the blending criteria.  This doesn't seem like an add to the total integration time for the final image... what do think?


Edited by Peregrinatum, 14 May 2021 - 12:21 PM.

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#2 Midnight Dan

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Posted 14 May 2021 - 11:17 AM

I think it "counts" for integration time, even thought it's different.  Time is time.  You always have to consider the equipment in use when comparing the integration time for various images.

 

5 hours of RGB integration will gather far more photons than 5 hours of NB integration.  Same with scope size, camera QE, f/ratio, etc.  If you're trying to compare two images, you have to take into account all the factors, not just integration time.  So if some of that time was spent on RGB and some on NB, that's just one more factor.  But the total integration time is all the time you were collecting photons, regardless of the equipment configuration.

 

-Dan


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#3 zakry3323

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Posted 14 May 2021 - 11:19 AM

Looking at it from that perspective, I'm not sure how much RGB should go into total integration time, if shooting LRGB, for the same reasons.

 

I suppose it's probably a bit subjective, depending upon how strongly the "primary" signal one is exposing for combines with the signal being blended with it. I suppose as long as it adds *some* data to the signal it should be counted as exposure time. In any case it's always nice to know total integration times per channel :)


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#4 elmiko

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Posted 14 May 2021 - 07:05 PM

Why wouldn't you count the data? 5 hours of narrowband or rgb. It's still added data.



#5 Peregrinatum

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Posted 14 May 2021 - 08:30 PM

Why wouldn't you count the data? 5 hours of narrowband or rgb. It's still added data.

well that's the thing, its not really added, it's either replaced pixel for pixel or a weighted average... for example, if the Ha was 10 hours and the R was 5 hours and half the R pixels were replaced by Ha then I could see it as an add equaling 7.5 hours of total integration, but not 15 hours as a direct sum... get my drift?!

 

it all depends on the what criteria is used for the blending


Edited by Peregrinatum, 14 May 2021 - 08:31 PM.

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#6 WadeH237

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Posted 14 May 2021 - 11:54 PM

well that's the thing, its not really added, it's either replaced pixel for pixel or a weighted average... for example, if the Ha was 10 hours and the R was 5 hours and half the R pixels were replaced by Ha then I could see it as an add equaling 7.5 hours of total integration, but not 15 hours as a direct sum... get my drift?!

 

it all depends on the what criteria is used for the blending

When I blend narrow band and broad band data, I don't replace pixels.  For pixels with Ha emission, I will blend the red filter data with the Ha filter data.

 

Sure, you could make the argument that by blending the data, you are taking away from the imaging time, but I don't really see it that way.  Any time you adjust the levels of one channel vs. another (ie. color balancing), you are doing the same thing.  This is also true of doing a non-linear stretch, where you are changing some pixel values by a different amount than others.

 

Finally, in most cases, when I blend RGB with narrow band, I am keeping the narrow band data for any nebulosity and using the RGB data for star colors.  In that case, I have very long total integration time on the nebula parts, but very little integration time on the RGB.  It doesn't take very long exposures to get good stars.


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#7 elmiko

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Posted 15 May 2021 - 12:36 AM

well that's the thing, its not really added, it's either replaced pixel for pixel or a weighted average... for example, if the Ha was 10 hours and the R was 5 hours and half the R pixels were replaced by Ha then I could see it as an add equaling 7.5 hours of total integration, but not 15 hours as a direct sum... get my drift?!

 

it all depends on the what criteria is used for the blending

Okay, I see where you are going with this. Kind of makes sense to me.  I just count all of my data doesn't matter if it's using one filter or the other. I use a osc though. Maybe I'm just not as technical.


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#8 TareqPhoto

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Posted 15 May 2021 - 07:15 AM

To me i prefer to think about adding and combining, not about replacing, i mean i use NB for NB signal not for replacing a wavelength in that region, so i won't use Ha only to make Red filter better or more appearance, no sense for me, but it is always nice to have extra data to add, i mean i saw results of Ha + RGB or SHO + RGB for example, they used each filter or channel for its purpose and bandwidth, so Ha for Ha and not for adding to red, most likely the only time i see where people want to replace something is when they shoot SHO and then RGB for stars only, to replace stars colors from SHO i think, but i didn't see a lot of people who are using Ha for Red replacement or OIII for Green/Blue filter replacing adding photons there, and why Ha and not SII for Red where that SII is more to red than Ha anyway.



#9 Midnight Dan

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Posted 15 May 2021 - 08:00 AM

well that's the thing, its not really added, it's either replaced pixel for pixel or a weighted average... for example, if the Ha was 10 hours and the R was 5 hours and half the R pixels were replaced by Ha then I could see it as an add equaling 7.5 hours of total integration, but not 15 hours as a direct sum... get my drift?!

 

it all depends on the what criteria is used for the blending

>> it's either replaced pixel for pixel or a weighted average

 

Doesn't matter.  Regular stacking will all RGB subs also averages.  And with PI, you can do a weighted average depending on sub characteristics.  And on hi dynamic range targets like the Orion nebula, people commonly combine a bunch of long exposure subs with short exposure subs, usually blending the two in some manner.

 

We combine images in all kinds of ways, whether from one type of filter or multiple types.  Again, Integration time is simply the time you spent collecting photons that went into the image.  The only time you don't count is for the subs you toss.

 

I'm not quite sure what your goal is in answering this question.  The only purpose in reporting integration time is to compare results from one image to another and see what effect integration time has.  But, as mentioned above, integration time cannot be taken in isolation and there are many other factors that come into that comparison.  

 

You can't compare integration time without knowing details about all the equipment in use, including filters.  If you see a total integration time that was reported for a combination of filters, then all bets are off unless you also know how much time was spent with each filter type.

 

-Dan



#10 Peregrinatum

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Posted 15 May 2021 - 02:58 PM

It's just something I was curious about, for example on my M101 project I will blend Ha with the R to try to capture the Ha cloud if present, I could do it a few different ways in PixelMath:

 

[1]  Ha*0.5 + R*0.5 = weighted average, adjust weights as desired

 

[2] max(Ha*x, R) = this would use the highest pixel value of each image for the new image, it would be a pixel replacement (x is a discretionary multiplier)

 

[3]  (Ha*75 - R*3)/(75-3) = new image that uses the bandwidths as weights, then this new image is used in a weighted average to taste with the R channel (there are variations on this method)

 

Again, just seems like the blending doesn't really add any integration time in a significant way, but it was just enhancing the R channel as desired.


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#11 WadeH237

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Posted 15 May 2021 - 03:09 PM

Again, just seems like the blending doesn't really add any integration time in a significant way, but it was just enhancing the R channel as desired.

How is enhancing the red channel not adding integration time?


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#12 Peregrinatum

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Posted 15 May 2021 - 03:14 PM

How is enhancing the red channel not adding integration time?

Not in a significant way imo, see my example above in post #5... however, it all depends on how the blend is done
 




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