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What Should My Unprocessed LIGHTS Physically Look Llike? (From a Light polluted sky)


Rickvanman

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I was wondering if any of you good folks might be kind enough to physically show me, and others, some examples of unprocessed LIGHT images from a DSLR (taken under medium light pollution), that can provide me with a point of visual reference? 

I'm looking for an approximate indication of the kind of 'look' I should be aiming to get on my DSLR screen at the end of a shot; Essentially trying to figure out where the threshold lies between a good, usable LIGHT image, and one that is over-exposed and has too much light pollution noise to be useful.  At this stage in my learning, trying to read-up on it is making my brain ache, so some actual  examples of what my unprocessed LIGHTS should physically look like, will be really useful.  

I live in a reasonably light polluted area (edge of a large Town).

 

Thanks in advance :)

 

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2 minutes ago, Rickvanman said:

Essentially trying to figure out where the threshold lies between a good, usable LIGHT image, and one that is over-exposed and has too much light pollution noise to be useful. 

If your camera offers a histogram view, I'd use that. Aim for peaks in the RGB channels between a quarter to a half way along.

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I can't help with a picture since I live at a dark site and use CCD, but guests sometimes ask me to look at data from quite heavy LP sights from their homes. Unprocessed they may look like a sheet of smooth bright orange with some stars and maybe hints of the brightest parts of a target. They can look utterly unusable but they're not. On one such example (the Iris Nebula) I opened a reference image of my own, opened the orange image in Pixinsight and placed just 5 DBE markers based on what my reference image said would be dark sky. I set a high tolerance value so the markers would pick up the orange and applied DBE. Bingo, once given an autostretch we had a perfectly good Iris on the screen complete with nice dusty background. I put the markers in each corner plus one near the middle.

Don't give up on gradient-filled data till you've run it through DBE!

Olly

Edited by ollypenrice
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28 minutes ago, pete_l said:

If your camera offers a histogram view, I'd use that. Aim for peaks in the RGB channels between a quarter to a half way along.

This is probably the best answer you'll get. Unprocessed lights can and will vary from image to image. It all depends on the speed of your scope (f ratio), if your using a light pollution filter and level of light pollution. 

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+1 for the histogram!

Hi Rick, if you are imaging unguided, you will need to keep your exposures fairly short and likely see less of your target in each sub... This doesn't necessarily mean it won't show up in the final picture. What I look for in a sub is the quality of the stars... In this first 30s sub of the Leo Triplet, the galaxies can be made out, but not much detail... However the stars are nice and small and not trailing (apart from some minor coma)DSC_0095.thumb.JPG.41e3c0a0fba3e4a77ee8c6c32f22754b.JPG

This next image however, you can still see the galaxies look pretty much the same but the stars are trailing.... This is the kind of sub I'd reject!DSC_0113.thumb.JPG.f236c37876b70ad02f1d72e37984b46d.JPG

Hope that helps, Art.

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1 hour ago, ollypenrice said:

I can't help with a picture since I live at a dark site and use CCD, but guests sometimes ask me to look at data from quite heavy LP sights from their homes. Unprocessed they may look like a sheet of smooth bright orange with some stars and maybe hints of the brightest parts of a target. They can look utterly unusable but they're not. On one such example (the Iris Nebula) I opened a reference image of my own, opened the orange image in Pixinsight and placed just 5 DBE markers based on what my reference image said would be dark sky. I set a high tolerance value so the markers would pick up the orange and applied DBE. Bingo, once given an autostretch we had a perfectly good Iris on the screen complete with nice dusty background. I put the markers in each corner plus one near the middle.

Don't give up on gradient-filled data till you've run it through DBE!

Olly

Thanks for the info Olly. What does DBE mean? - Thanks

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7 minutes ago, Rickvanman said:

Thanks for the info Olly. What does DBE mean? - Thanks

Dynamic Background Extraction. You put markers onto the image where the sky should be neutral background without stars or objects. You then ask Pixinsight to make a model of your colour gradient, which it does. If your main image looks like a sheet of orange then the model will look like a sheet of orange. If your image is rather green on one side and rather red on the other (which is common for me) then the model will, again, be green on one side and red on the other.

You then ask PI to subtract the model from the original picture, leaving (with luck!) a nice neutral background sky and well calibrated colour balance all the way up to the stellar cores.

Check out the demos by that most excellent man Mr Harry Page. Here he is demonstrating DBE. http://www.harrysastroshed.com/pixinsight/pixinsight video files/2013 pix vids/dbe/dbe.mp4

Olly

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50 minutes ago, ollypenrice said:

Dynamic Background Extraction. You put markers onto the image where the sky should be neutral background without stars or objects. You then ask Pixinsight to make a model of your colour gradient, which it does. If your main image looks like a sheet of orange then the model will look like a sheet of orange. If your image is rather green on one side and rather red on the other (which is common for me) then the model will, again, be green on one side and red on the other.

You then ask PI to subtract the model from the original picture, leaving (with luck!) a nice neutral background sky and well calibrated colour balance all the way up to the stellar cores.

Check out the demos by that most excellent man Mr Harry Page. Here he is demonstrating DBE. http://www.harrysastroshed.com/pixinsight/pixinsight video files/2013 pix vids/dbe/dbe.mp4

Olly

Thanks Olly, i'll check it out :)

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43 minutes ago, Rickvanman said:

Thanks Olly, i'll check it out :)

If you don't have PI, you can do this in Photoshop too... Though it's a little more long winded... What programs are you using to process your images Rick?

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46 minutes ago, Art Gecko said:

If you don't have PI, you can do this in Photoshop too... Though it's a little more long winded... What programs are you using to process your images Rick?

Yes, there's a good plug-in called Gradient Xterminator by Russ Croman but DBE is the weapon of choice for me.

Olly

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For me as an imager the software is probably more important than the hardware. If I shot data in a budget setup and had access to the prime software, or shot the data in prime hardware but couldn't use the prime software, the budget hardware image would be the better of the two. Software matters.

Olly

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Lights can look incredibly unimpressive, what is odd is the internal pre-processing means the image on the preview screen looks much clearer, I assume it displays what would be put into a jpg version. This is a CR2 RAW saved as  PNG without any processing:

59457e4d18943_Rosette(44).thumb.png.986b0be535a430e869ae656223e1934b.png

It seems amazing that anything's hidden in there at all, but it is!

594581c9d2960_RosetteNebula.thumb.png.832d90f0a84736ef5c6e6fd26eafd9c0.png

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On 17/06/2017 at 16:49, Art Gecko said:

If you don't have PI, you can do this in Photoshop too... Though it's a little more long winded... What programs are you using to process your images Rick?

For now I'm doing everything in photoshop elements 14. Although I'm tweaking the images in DSS prior to saving them. 

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On 21/06/2017 at 14:21, Rickvanman said:

For now I'm doing everything in photoshop elements 14. Although I'm tweaking the images in DSS prior to saving them. 

I'm guessing Ps elements is basically the same as full photoshop but with a few advanced features removed? I have an example for you if you don't have Gradient XTerminator...

Here's a shot I captured the other night with an unmodded DSLR, on one of the shortest, hottest nights of the year, where the sky didn't even reach full darkness and the street lights just served to illuminate it even more... So what we'd call the exact opposite of perfect conditions!.. I've stacked 66x20s subs with darks and flats, saved it as 16bit TIFF uncompressed and untweaked in DSS (nothing else, just stacked and saved) then opened it in Ps (mine is CS5, yours may look different)594bca9a15d88_Screenshot2017-06-22at14_32_00.thumb.png.280f5245b3b75a6c0816c7ceb7005c67.png

You can't see anything yet so lets do a stretch.... Image> Adjustments> Curves:594bcae443726_Screenshot2017-06-22at14_32_54.thumb.png.29463d8b0233cfad596ca495ba318128.png

Starting to see the dumbbell nebula now, but it's all very light polluted as we'd expect from the shooting conditions, so I'll use the levels to set the colour, this is a quick and easy way: Image> Adjustments> Levels... Double click on the black point eyedropper594bcb491a31e_Screenshot2017-06-22at14_33_25.thumb.png.4591911e9d4eef9414cb7701d573f1f2.png

Set your RGB to 35,35,35:594bcbf217c30_Screenshot2017-06-22at14_33_34.thumb.png.63d0dbfc0c62917e39489ef21e0f6f51.png

Now use the eyedropper on the background, near the target where there are no stars and watch what happens:594bcc686343b_Screenshot2017-06-22at14_33_59.thumb.png.281a9e6f6157d722fc757f7499ab1acc.png

pretty good yeah? If your data is good, you could probably stop here and have a reasonable image after a few tweaks.... but lets go a step or two further for the sake of it and see just how much we can pull out of it.... To keep things simple we won't bother with star mask layers and all that.... We'll just give it another stretch:594bcd7bdb147_Screenshot2017-06-22at14_34_44.thumb.png.b584bb3c839f38f1dd8f36aeb2e4fad8.png

Now that's really pulling some colour out of it!!!... Some might say I'm probably over stretching this now, but to show you how a bad gradient can be corrected.. I'm stretching it until I can see a bad gradient.. it's just an example.... So now we duplicate the layer:594bcded6211a_Screenshot2017-06-22at14_35_22.thumb.png.306ad7bd02f8cae4e903df28b5379fa0.png

This is where we get rid of that horrible orange for good! Go to Filter> Noise> Dust and Scratches... then move the top slider all the way over to the right:594bd3c2c89d3_Screenshot2017-06-22at14_37_35.thumb.png.86f997dbead4c4bbfe00b69fcf433a62.png

Looks good now doesn't it! Don't worry... next use the clone stamp tool to get rid of the smudge that is the nebula, and maybe apply a little gaussian blur:594bd46bc45b4_Screenshot2017-06-22at14_39_09.thumb.png.b618004775d1622c10fcfec6a502b3b8.png

Then in the Layers menu, where it says where it says Blending options, open it and hit subtract..... Boom!594bd4ca65913_Screenshot2017-06-22at14_39_36.thumb.png.299c4f8c4eaa79d7f3790ddbbecdc17f.png

I did one last thing and lowered the opacity of the duplicate layer just to stop it clipping the blacks too far... But you could now flatten that down to one layer and just have a tweak with the colours or sharpness or whatever you want to do.... Mine is not the best image in the world, but just thought I'd show an example of what can be squeezed out of less than desirable conditions.... Everyone has their own ways of doing things, maybe some folks will say I'm doing it completely wrong?!... It works for me at my level of AP (entry level unguided imaging) and I hope it'll help you along with all the other advice these good people may share with you.

Best of luck, Art

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As gradient exterminator works in paint shop pro I imagine it will also work in the OPs software.

In addition to the great post above, if not already mentioned budgetastro.net had tutorials you can follow using DSS and your photo elements. The tutorials use photoshop but it's surprising how much other software can do to that's the same.

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1 hour ago, Stub Mandrel said:

Excellent tutorial, although I think the final gradient removal lost some of the faint nebulosity I'm sure that was only because it was against the clock!

Thanks Neil, yeah I wouldn't recommend going at it quite that aggressively.... More of a demonstration piece!

The solution would be to add a layer mask to the duplicate layer and paint over the nebula with a soft brush on the layer mask to reveal the hidden nebulosity.... but there are plenty of other tutorials for that kind of thing :happy7:

Edited by Art Gecko
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On 22/06/2017 at 15:59, Art Gecko said:

I'm guessing Ps elements is basically the same as full photoshop but with a few advanced features removed? I have an example for you if you don't have Gradient XTerminator...

Here's a shot I captured the other night with an unmodded DSLR, on one of the shortest, hottest nights of the year, where the sky didn't even reach full darkness and the street lights just served to illuminate it even more... So what we'd call the exact opposite of perfect conditions!.. I've stacked 66x20s subs with darks and flats, saved it as 16bit TIFF uncompressed and untweaked in DSS (nothing else, just stacked and saved) then opened it in Ps (mine is CS5, yours may look different)594bca9a15d88_Screenshot2017-06-22at14_32_00.thumb.png.280f5245b3b75a6c0816c7ceb7005c67.png

You can't see anything yet so lets do a stretch.... Image> Adjustments> Curves:594bcae443726_Screenshot2017-06-22at14_32_54.thumb.png.29463d8b0233cfad596ca495ba318128.png

Starting to see the dumbbell nebula now, but it's all very light polluted as we'd expect from the shooting conditions, so I'll use the levels to set the colour, this is a quick and easy way: Image> Adjustments> Levels... Double click on the black point eyedropper594bcb491a31e_Screenshot2017-06-22at14_33_25.thumb.png.4591911e9d4eef9414cb7701d573f1f2.png

Set your RGB to 35,35,35:594bcbf217c30_Screenshot2017-06-22at14_33_34.thumb.png.63d0dbfc0c62917e39489ef21e0f6f51.png

Now use the eyedropper on the background, near the target where there are no stars and watch what happens:594bcc686343b_Screenshot2017-06-22at14_33_59.thumb.png.281a9e6f6157d722fc757f7499ab1acc.png

pretty good yeah? If your data is good, you could probably stop here and have a reasonable image after a few tweaks.... but lets go a step or two further for the sake of it and see just how much we can pull out of it.... To keep things simple we won't bother with star mask layers and all that.... We'll just give it another stretch:594bcd7bdb147_Screenshot2017-06-22at14_34_44.thumb.png.b584bb3c839f38f1dd8f36aeb2e4fad8.png

Now that's really pulling some colour out of it!!!... Some might say I'm probably over stretching this now, but to show you how a bad gradient can be corrected.. I'm stretching it until I can see a bad gradient.. it's just an example.... So now we duplicate the layer:594bcded6211a_Screenshot2017-06-22at14_35_22.thumb.png.306ad7bd02f8cae4e903df28b5379fa0.png

This is where we get rid of that horrible orange for good! Go to Filter> Noise> Dust and Scratches... then move the top slider all the way over to the right:594bd3c2c89d3_Screenshot2017-06-22at14_37_35.thumb.png.86f997dbead4c4bbfe00b69fcf433a62.png

Looks good now doesn't it! Don't worry... next use the clone stamp tool to get rid of the smudge that is the nebula, and maybe apply a little gaussian blur:594bd46bc45b4_Screenshot2017-06-22at14_39_09.thumb.png.b618004775d1622c10fcfec6a502b3b8.png

Then in the Layers menu, where it says where it says Blending options, open it and hit subtract..... Boom!594bd4ca65913_Screenshot2017-06-22at14_39_36.thumb.png.299c4f8c4eaa79d7f3790ddbbecdc17f.png

I did one last thing and lowered the opacity of the duplicate layer just to stop it clipping the blacks too far... But you could now flatten that down to one layer and just have a tweak with the colours or sharpness or whatever you want to do.... Mine is not the best image in the world, but just thought I'd show an example of what can be squeezed out of less than desirable conditions.... Everyone has their own ways of doing things, maybe some folks will say I'm doing it completely wrong?!... It works for me at my level of AP (entry level unguided imaging) and I hope it'll help you along with all the other advice these good people may share with you.

Best of luck, Art

 Thanks for the tutorial, Art,  that's fantastic!

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On 17/06/2017 at 12:47, Rickvanman said:

I was wondering if any of you good folks might be kind enough to physically show me, and others, some examples of unprocessed LIGHT images from a DSLR (taken under medium light pollution), that can provide me with a point of visual reference? 

I'm looking for an approximate indication of the kind of 'look' I should be aiming to get on my DSLR screen at the end of a shot; Essentially trying to figure out where the threshold lies between a good, usable LIGHT image, and one that is over-exposed and has too much light pollution noise to be useful.  At this stage in my learning, trying to read-up on it is making my brain ache, so some actual  examples of what my unprocessed LIGHTS should physically look like, will be really useful.  

I live in a reasonably light polluted area (edge of a large Town).

 

Thanks in advance :)

 

Use the in camera histogram, if it's a Canon, it's under the info button.

Aim to get the white luminance histogram to at least 20% and certainly no more than 50%.
The range 20>40% is normally ok.

Here is an example off a Canon 60Da with a CLS Clip filter.
The white luminance histogram is approx 25%, you can see it was a 10minute exposure but was a particularly
dark clear night here. The usual histogram with all the LP here would be in the same place at 5minutes.

info.jpg

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