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Over-exposed stacked image. Any easy PS solutions ??


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Evening all,

On these blustery, cloud heavy nights I can easily lose a few hours trawling through my past captures trying to eek out a bit more texture and contrast if I can.

The Atik 414ex is such a sensitive little beast that it can over expose emission nebula with  only 1 mins subs.   Case in point is the following stacked image of the Dumbell Nebula

( M27) in Oxygen III.

1639856711_exampleo303.thumb.jpg.67d89512c8bb3e5c90ba8972e2a37326.jpg

That bright patch of gas is the problem,  it dominates any HST or  Bi-colour image I try to create from it.

Is there any (easy) way to nullify its effect in PhotoShop ??  ( I am quite thick when it comes to the theory of PS).

I have tried with the slow cyclic adjustments of  levels and  curves. Tweeking, saving, tweeking a bit more ...etc  and it helps initially but if pushed too far will  mess up other finer details in the outer nebula.

Any help much appreciated.

Thanks,

 

sean.

 

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Maybe try taking shorter subs for the overexposed section and then layer it over the top. 

I used it in two thread series where I was imaging Orion in 2014/15 to get the core:

I'm not sure if you can recover it in PS, someone else may be able to help there.

 

 

Edited by Robp
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Thanks  @Robp   , Yes I have the same problem with the core of M31 as well the Orion Nebula in the normal RGB wavebands..

I will probably have to bite the bullet and learn how to 'layer' and 'mask' .....

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If the data isn't over exposed when you start processing, you should be able to prevent it.

If it is there when you start, you may have no choice but to go for the extra short subs. I also had problems with M31 and went the short sub route for the core only.

I used this guide for the short sub/long sub layering:

http://www.astropix.com/html/j_digit/laymask.html

Hopefully someone with a better understanding of ps than me will be along to help without the need of extra data ?

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Agree with the above, if the unstretched core is saturated there really is little you can do other than blur it a little.  I'm surprise if that is the case with just 1 minute subs in OIII.  If the problem is that it is becoming saturated on minimal stretching then layer masking is the answer.  Worth looking at at Ron's link because layer masks are a very powerful, useful tool.

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Same thing happened on this Bi colour Ha -OIII Crab shot..... I think this one was from 4x3mins with the 10"F4....

those blue filaments are from the OIII stack

2068469037_Crab2nights10f4Ha-OIII8012BiColorImage.jpg.70f37a5ebd0842cd5e12dd8a7d820bed.jpg

Maybe I have got a hole in my OIII filter ?     ;)

 

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Something's wrong here. I used 30 minute subs on M27 in OIII! A 10 inch F4 is putting a lot of light on a small number of pixels but even so... (Mine was in a 14 inch F6.8. That cannot account for what we are seeing.)

Could you crop out the main nebula to reduce file size and post a link to the linear FITS stack in OIII? Or, alternatively, take the linear stack just as it is, convert it to JPEG and post it here?

Joking apart, perhaps your filter does have a problem. If it were failing to block part of the IR spectrum then all would be revealed.

Occasionally, but only very occasionally, I've found it necessary to shoot short exposures. The Trapezium and the Cat's Eye certainly, M31 maybe/maybe not and, for the rest, I can usually blend a hard and a soft stretch of the same data. The Jerry Lodigruss method in the earlier link is superb.

Olly

Edited by ollypenrice
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1 hour ago, ollypenrice said:

Something's wrong here. I used 30 minute subs on M27 in OIII! A 10 inch F4 is putting a lot of light on a small number of pixels but even so... (Mine was in a 14 inch F6.8. That cannot account for what we are seeing.)

Could you crop out the main nebula to reduce file size and post a link to the linear FITS stack in OIII? Or, alternatively, take the linear stack just as it is, convert it to JPEG and post it here?

Joking apart, perhaps your filter does have a problem. If it were failing to block part of the IR spectrum then all would be revealed.

Occasionally, but only very occasionally, I've found it necessary to shoot short exposures. The Trapezium and the Cat's Eye certainly, M31 maybe/maybe not and, for the rest, I can usually blend a hard and a soft stretch of the same data. The Jerry Lodigruss method in the earlier link is superb.

Olly

+1! I couldn't manage without layer masks for astro or regular photography. Learn this simple technique and it will change the way you approach imaging generally, allowing to to maximize DR on just about any image selectively and creatively without resorting to (IMHO) largely unsatisfactory automatic HDR methods. Having said that, HDR composition in PI can produce great results, especially on lum and HA stacks comprising of multiple exposure times. The tutorial at http://www.lightvortexastronomy.com/tutorial-producing-an-hdr-image.html is an excellent one. 

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7 minutes ago, RichLD said:

+1! I couldn't manage without layer masks for astro or regular photography. Learn this simple technique and it will change the way you approach imaging generally, allowing to to maximize DR on just about any image selectively and creatively without resorting to (IMHO) largely unsatisfactory automatic HDR methods. Having said that, HDR composition in PI can produce great results, especially on lum and HA stacks comprising of multiple exposure times. The tutorial at http://www.lightvortexastronomy.com/tutorial-producing-an-hdr-image.html is an excellent one. 

Yup, I think manual layer masking is a beautiful and satisfying technique allowing you to manage the blend just as you wish to. I do have an HDR package but use it only for creating deliberately unrealistic or slightly surreal daytime pictures.*

Olly

* Badly, I should add! :D

Edited by ollypenrice
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6 hours ago, ollypenrice said:

...... take the linear stack just as it is, convert it to JPEG and post it here? 

Thanks Olly.   I was only kidding when I said the filter had a hole !!... now you have me worrying it has !!

With regard to the linear stack, the Dumbell pic in the original post is the output from DSS  converted to a Jpeg. I cannot remember if I stretched it in DSS, but I suspect I didn't, because there is a lot of detail there, but I will check.

 When I am at home I will dig out the original stacked TIFF   ( yes I use TIFF..... is that a bad thing ?? ),  crop it a bit and post it.

Regrds,

Sean.

 

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Here is the "raw"*** stacked TIF file  (O3)  from DSS for the Dumbell. 

Once I have stacked the subs I tend to delete them to save space. It would have been useful to have the originals floating around.

FINAL DUMB 22 mins 10f4 03.tif

(  *** Without DSS tweeking, but I am wondering if I might have done an "AutoTone" and "AutoContrast" on this in Photoshop and forgot I did it !!!!

  There is an unfamiliar amount of detail in the outer cloud to be "sans processing",  this could be a senior moment on my behalf....)

Maybe this is a self generated issue,  but  I will definitely learn the layering and masking techniques to blend images.

 

S.

Edited by Craney
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I would definitely suggest keeping the subs stored if you can, even on an external hard drive or something.

You can add to subs over many nights, even years to constantly improve the image and there have been many times when I have noticed a mistake in the stack half way through a process flow and had to go back and stack again.

I will let someone more experienced analyse the tif file, but it doesn't look right to me.

 

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I agree with the above - I suspect you have "Apply adjustments to the saved image" selected in DSS. It's a radio button in the "Save As" dialog.

If you're lucky, you may find the original (unadjusted) stacks on your HDD named "Autosave.tif".

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