Lacking in contrast!

[Rustang]

Ive been meaning to look into this for ages just to confirm if it is what it is or if I'm missing something. Its in regards to the contrast of nebulosity against the dark sky in my data as Ive always felt its a little to grey across the board. It could just be that that's what my equipment produces so I'm just looking to check if that's the case or not as I normally see alot more contrast in pretty much everyone else's data.

Its a QHY9 mono CCD camera that I'm using with baader NB filters so first I want to check if the issue is down to the sensitivity of this particular camera!? I capture at - 20, gain 9 offset 109. Adam (the cameras previous owner) kindly helped me with what settings to use etc and I've been taking 10 min exposures after discussing this with him. I wanted to double check if in my bortle 6 skies whether or not 10min subs could just be to long and washing things out a little?

Processing - I appreciate that it could be down to simply the processing of the data but I'm not necessarily convinced by this, I have an example below of some stacked Ha data with some basic levels/curves adjustment and its pretty grey across the board still. At this stage I have to really start working hard to get a decent dark sky (not black) behind the nebulosity and that's been the case since owning the camera. I only purchased the camera back in February this year so still pretty new to narrowband imaging so have stayed in the comfort zone of what settings to use, I wouldn't really know where to start if I was going to change anything!

 

I'm not necessarily bothered and Ive been really pleased with the images Ive been getting with the camera but if there is anyway of helping things along I'm all ears!

 

 

Edited June 25, 2021 by Rustang

[CraigT82]

If you ask me that's a fabulous image! A lot of the work I see online is well overcooked (not so much on here but on other social media platforms) with contrast and saturation boosted to the max and a ton of sharpening and noise reduction thrown on top, which makes them look reasonably impressive at first glance in a preview, but not so nice when viewed at full size. 

Your posted image is the opposite of that in my opinion, conservatively processed, balanced and sympathetic to the data. A joy to look at. 

I think that a little more time on this particular image with the curves tool and you could get the look you're after without sacrificing the data? 

 

[david_taurus83]

A gradient wipe would do wonders with that. Here's what a simple S curve will do on my phone.

 

[Rustang]

3 minutes ago, CraigT82 said:

If you ask me that's a fabulous image! A lot of the work I see online is well overcooked (not so much on here but on other social media platforms) with contrast and saturation boosted to the max and a ton of sharpening and noise reduction thrown on top, which makes them look reasonably impressive at first glance in a preview, but not so nice when viewed at full size. 

Your posted image is the opposite of that in my opinion, conservatively processed, balanced and sympathetic to the data. A joy to look at. 

I think that a little more time on this particular image with the curves tool and you could get the look you're after without sacrificing the data? 

 

Thanks, i appreciate the comments. It's more so that I'm not sure if all the other data I see here there and everywhere always looks like it has more contrast between the sky and nebulosity given a sharper looking image, I don't think it's always necessarily how it's processed I just get the feeling it could be down to more sensitive sensors or something else. I understand totally what you mean about some over cooked images, I would just prefer some more contrast at the beginning to work the data so hard. 

[Rustang]

10 minutes ago, david_taurus83 said:

A gradient wipe would do wonders with that. Here's what a simple S curve will do on my phone.

 

Thanks, I normally get somewhere close to what I like but I really have to work things harder than I'm sure I should have too! 

Edited June 25, 2021 by Rustang

[vlaiv]

1 hour ago, Rustang said:

I appreciate that it could be down to simply the processing of the data but I'm not necessarily convinced by this,

Will this convince you?

[Rustang]

3 minutes ago, vlaiv said:

Will this convince you?

I've posted the final result with this data in the deep sky imaging section, I'm not sure if I'm explaining myself properly 😊  but to get a decent result for me starts to have an effect on the quality of some of my images, as said I have a feeling its down the to sensitivity of the sensor as most other images I see have a crisper, better contrast that doesn't seem have an effect on the quality of the image, the more curves and stretching I do to gain contrast starts to effect things. It could just be me/the equipment I have but I just wanted to make sure I could change a setting/do something different somewhere that's all. 

[david_taurus83]

2 minutes ago, Rustang said:

I've posted the final result with this data in the deep sky imaging section, I'm not sure if I'm explaining myself properly 😊  but to get a decent result for me starts to have an effect on the quality of some of my images, as said I have a feeling its down the to sensitivity of the sensor as most other images I see have a crisper, better contrast that doesn't seem have an effect on the quality of the image, the more curves and stretching I do to gain contrast starts to effect things. It could just be me/the equipment I have but I just wanted to make sure I could change a setting/do something different somewhere that's all. 

Are you comparing your images to others using the same camera/sensor? I'm not sure what exactly your asking?

[Nik271]

The sky brightness may play a role too. A lot of the light pollution these days is in all the spectrum because of the LED lights.  Perhaps you are comparing with images taken from darker skies or in better conditions?

[Rustang]

32 minutes ago, david_taurus83 said:

Are you comparing your images to others using the same camera/sensor? I'm not sure what exactly your asking?

Your right to ask this as I fully understand that equipment used will have a difference and its probably wrong to generally compare against others images like I'm doing so it's probably factor's such as equipment, quality of sky etc but I just wanted to make sure I'm not missing anything else. I have to say, Adam the previous owner of the camera has also produced the results I'm seeing often that I can't seem to achieve, you could straight away say then it's the processing so maybe I'm missing something there but it's a certain crispness to the contrast between the nebulosity and sky that looks alot smoother as to get anything close it adds more noise for me. I'm more than happy to except it could be lack of experience 😊

Edited June 25, 2021 by Rustang

[Rustang]

9 minutes ago, Nik271 said:

The sky brightness may play a role too. A lot of the light pollution these days is in all the spectrum because of the LED lights.  Perhaps you are comparing with images taken from darker skies or in better conditions?

You could be right, I'm just trying to narrow down the factors it could be and hopefully it's not me worrying about nothing. 

[david_taurus83]

I think the previous owner lives in a nice dark spot!

[Rustang]

11 minutes ago, david_taurus83 said:

I think the previous owner lives in a nice dark spot!

Very true 😊

[vlaiv]

1 hour ago, Rustang said:

I'm more than happy to except it could be lack of experience

I think that this can be easily "measured".

You can for example - post linear stack in 32bit fits format and people can then process that data. You can then compare your processing to see if it can be improved.

I agree with above - sky quality plays significant role for image quality - as does telescope used with camera (aperture at resolution). So does total integration time.

However, this is narrow band image and I don't know how much of light pollution gets thru. Maybe people whose images you look at - have good denoising skills? That lets them push data further without revealing too much of artifacts.

[Rustang]

6 minutes ago, vlaiv said:

I think that this can be easily "measured".

You can for example - post linear stack in 32bit fits format and people can then process that data. You can then compare your processing to see if it can be improved.

I agree with above - sky quality plays significant role for image quality - as does telescope used with camera (aperture at resolution). So does total integration time.

However, this is narrow band image and I don't know how much of light pollution gets thru. Maybe people whose images you look at - have good denoising skills? That lets them push data further without revealing too much of artifacts.

Thanks, il look at posting a stack tomorrow. I think I calculated that my setup could be under sampling which may not be helping also but that's going into territory that's starting to go way over my head! 😊

[vlaiv]

5 minutes ago, Rustang said:

Thanks, il look at posting a stack tomorrow. I think I calculated that my setup could be under sampling which may not be helping also but that's going into territory that's starting to go way over my head! 😊

Actually - being under sampled helps the quality of your image (or rather SNR) so don't worry about that.

[Rustang]

1 minute ago, vlaiv said:

Actually - being under sampled helps the quality of your image (or rather SNR) so don't worry about that. 

That's good to know then 🙂

[wimvb]

I loaded the jpeg into PixInsight and had a look at the histogram.

The lower histogram is your image, the upper is with the black point taken in a bit. You have a large amount of unused dynamic range in your image. The black point can be brought in to 0.12 without clipping any data, which means that you throw away about 1/8 of your dynamic range. In a B/W image, that usually is not a good thing, but if you combine this image with other images to get a colour image, that may be ok. It depends on what you want the final image to look like.

Here are two examples of easy things to do:

1. just the black point adjusted to below clipping, no further stretching (S-curves or anything similar)

2. removed a possible gradient, and adjusted the black point

If you want to further enhance this image, you can start experimenting with local contrast enhancements or high dynamic range processing. That's all a matter of taste. If this is going to be part of a colour image, I wouldn't do that though.

[wimvb]

And the last image (DBE + black point) with an added S-curve, lowering the histogram peak to 0.075 and leaving the higher range unaltered. This isolates the main target a bit better, and gives a bit more drama. But again, it all depends on where you want to take the data.

[tooth_dr]

@Rustang I haven’t been posting on the forum just as frequently, only seeing this thread now. I do live at a good Bortle 4 site for sure which helps. But to be honest I’ve looked at all the images you’ve produced with the camera and I’m very very impressed. Your processing is very natural and your images don’t lack contrast.  

[ollypenrice]

This is, with absolutely no doubt whatever, a processing issue.  It has nothing to do with capture.  Others have demonstrated the potential for higher contrast contained in the data.  However, we can point you towards the processing techniques which will enhance both global and local contrasts but the extent to which you apply them will remain your call. Many images strike me as over-processed in the way Craig T82 describes above. So I'll give you a couple of ways to enhance contrast but don't take that as my saying you should use them. Make your own picture. Wim has covered the black point so let's look at...

The stretch:

When we stretch an image we do so non-linearly, so we stretch the dark parts by far more than the light parts, so increasing contrast in the dark parts. That's how we extract the nebulosity from the background. However, different stretches will give different levels of contrast. If you stretch in Levels you'll get a logarithmic stretch which looks something like this when seen in Curves:

This is a gentle curve and the difference in stretch between the red and blue lines shows the difference in stretch between those points. This will give a natural looking image with moderate contrasts.

The alternative is an aggressive stretch.:

Here all the contrasts between dark and moderate signal have been massively increased. Note the difference in stretch between red and blue. That difference is contrast.

I've shown this stretch before on here and it has raised eyebrows and disapproval but it remains one of my go-to operations, above all in narrowband where its increase of star size is not such an issue. When I demo these curves on this data with guests, most prefer the hard stretch. It was the stretch used in the Ha and OIII of this final version: https://www.astrobin.com/327970/

If you use Photoshop consider Noel's Actions (now called Pro Digital Astronomy Tools) which has an excellent routine called Local Contrast Enhancement. In Pixinsight try Local Contrast Equalization (which you can also replicate in Photoshop.)

Olly

 

[Rustang]

8 hours ago, wimvb said:

And the last image (DBE + black point) with an added S-curve, lowering the histogram peak to 0.075 and leaving the higher range unaltered. This isolates the main target a bit better, and gives a bit more drama. But again, it all depends on where you want to take the data.

Thanks for all the info, I should have explained that the above image I posted wasn't fully processed but was to show where I get to before taking it further but then adding issues such as noise so its probably my processing techniques that need some improvements. You have definitely managed to lose the washed out feel and brought out the darker sky in places I missed even in the final colour image I posted! . Il have some more goes at my recent data which hasn't been helped by the lighter nights. 

[Rustang]

1 hour ago, tooth_dr said:

@Rustang I haven’t been posting on the forum just as frequently, only seeing this thread now. I do live at a good Bortle 4 site for sure which helps. But to be honest I’ve looked at all the images you’ve produced with the camera and I’m very very impressed. Your processing is very natural and your images don’t lack contrast.  

Thanks Adam, first and foremost I'm still really happy with my purchase 😊 I saw on your Camera sale thread that you have lost some interest in the hobby which is a shame but I fully understand that it's not for the faint hearted and needs a certain degree of dedication. When you get issues such as software it really does start to gripe so it's understandable, I hope you find a drive to keep going with it. I'm starting to understand the factors of my concerns and there are probably a few, some in my control and some not, I'm certainly a little lazy on my intergration time and I'm probably worrying to much about nothing but I'm always looking to improve 🙂

[Rustang]

55 minutes ago, ollypenrice said:

This is, with absolutely no doubt whatever, a processing issue.  It has nothing to do with capture.  Others have demonstrated the potential for higher contrast contained in the data.  However, we can point you towards the processing techniques which will enhance both global and local contrasts but the extent to which you apply them will remain your call. Many images strike me as over-processed in the way Craig T82 describes above. So I'll give you a couple of ways to enhance contrast but don't take that as my saying you should use them. Make your own picture. Wim has covered the black point so let's look at...

The stretch:

When we stretch an image we do so non-linearly, so we stretch the dark parts by far more than the light parts, so increasing contrast in the dark parts. That's how we extract the nebulosity from the background. However, different stretches will give different levels of contrast. If you stretch in Levels you'll get a logarithmic stretch which looks something like this when seen in Curves:

This is a gentle curve and the difference in stretch between the red and blue lines shows the difference in stretch between those points. This will give a natural looking image with moderate contrasts.

The alternative is an aggressive stretch.:

Here all the contrasts between dark and moderate signal have been massively increased. Note the difference in stretch between red and blue. That difference is contrast.

I've shown this stretch before on here and it has raised eyebrows and disapproval but it remains one of my go-to operations, above all in narrowband where its increase of star size is not such an issue. When I demo these curves on this data with guests, most prefer the hard stretch. It was the stretch used in the Ha and OIII of this final version: https://www.astrobin.com/327970/

If you use Photoshop consider Noel's Actions (now called Pro Digital Astronomy Tools) which has an excellent routine called Local Contrast Enhancement. In Pixinsight try Local Contrast Equalization (which you can also replicate in Photoshop.)

Olly

 

Thanks Olly, il take a look into that, just to clarify again my above Ha data was not fully processed it was just to show where I start getting to before then processing further but it can then sometimes start adding issues with noise etc. It certainly seems I have some improvements in processing to learn. I normally do levels adjustments first brining in the light and dark slider but that never really helps with contrast, it's the curves that helps the most but I'm not getting to far by then with the data. 

Edited June 26, 2021 by Rustang

[Rustang]

Thanks for all your help guys, il start looking into my processing techniques to see if I can improve on them.