Noise and banding issues with 645Z - help requested

[Ed Hurst]

Hello chums,

As ever when I experience a knotty and intractable problem, I turn (after trying a range of solutions) to this wonder brain's trust for advice and help.

I am a big fan of my 645Z in many ways. It has transformed my photography, even by comparison to the 645D + D800E I was using previously. However, I am finding a couple of problems that are very frustrating given how I tend to shoot.

Firstly, when shooting high contrast scenes (which is often the case around sunrise/sunset, where parts of the scene tend to be very dark and light), it has for many years been my practice to bracket +/-2 stops then layer the files and brush selectively using layer masks. It has worked well with every digital camera I have used, from 1Dsii and 5Dii to 645D. However, with the Z, I find that this has become problematic. The dark areas tend to be very noisy, which is counter to my general experience that there is low noise and high DR on this camera. Layering in a lighter exposure and brushing those areas in seems only to accentuate the noise, until I brush the areas in so much that they are so light that the noise doesn't show up (which of course is not my intention, as I want those areas to look relatively dark in the scene). I can make it work by allowing those areas to become very light, then darkening them again using curves, but that seems counter to the very benefits of this camera and I can't believe it should be necessary.

Look at the bottom right hand area of this picture for the effect I mean. This happens a lot. In this case, I layered in a lighter exposure for that area - which in the past has mean a nice noise-free image for the dark places:

[/url]_IMG0725Step4sRGBSMALL by Ed Hurst, on Flickr[/IMG]

Furthermore, I have noticed that skies tend to be prone to banding. Here is an example:

[/url]_IMG2089Step5sRGBSMALL by Ed Hurst, on Flickr[/IMG]

That banding in the sky is not a result of JPG compression or Flickr crushing the file - it's there on the 16 bit TIFF.

Now I will admit that I tend to edit fairly vigorously, but no more so that I have always done without this occurring. So I am flummoxed. Is it a problem with the sensor (I have tried two different 645Zs, with the same results)? Can I change my technique somewhat to get around this? I have tried using Prophoto colour space in case it's about that somehow (it didn't help). I do all my processing in 16 bit mode.

All advice gratefully received!

Ed

 

[Kabraxis]

Hi Ed, there is a very long thread @Pentaxforums.com about the problem.

Maybe you will find your solution there:
http://www.pentaxforums.com/forums/...ing-strange-colour-shifts-sky-highlights.html

Regards
Pascal

 

[Kolor-Pikker]

Hi Ed, there is a very long thread @Pentaxforums.com about the problem.

Maybe you will find your solution there:
http://www.pentaxforums.com/forums/...ing-strange-colour-shifts-sky-highlights.html

Regards
Pascal

Some of the posts there are by me, the topic intrigued me since I had a 645Z too and was concerned that I might run into something like that. What I do know is that it occurs with intense colors near the limit of RGB gamut, and if one or two or of chroma channels got clipped, but having inspected hundreds of images over 8 months and done specific testing, and I've never ran into banding or noise problems.

In fact, almost every HDR I've shot I ended up using only one exposure with shadow push, the added noise in the extreme shadows was so little and so difficult to see even at 100% on a 1440p 27" monitor, that it just wasn't worth my time to do blending.

Speaking of which, the person who had this problem on Pentax Forums shot those images in New Zealand, so... I dunno, maybe it's something about your down under skies? On thing's for sure, where I live we never have skies nearly as intense in color as what I see from Aus/NZ, so that limits my testing capabilities.

Try downloading RawDigger and analyzing the Raw histogram of the shot with banding, it could be that some of the color channels are clipped, but you simply don't know it because of auto white balance.

 

[Ed Hurst]

I just want to say thanks to you all for your help and advice. I have not got this licked yet, but I am making progress. I'll continue doing testing and report back when I have had the time to spend more time. But one thing is already clear - if I lighten the dark areas within a single file, they are remarkably noise free. It's trying to adjust the tonal values within those areas - especially if I want them to end up being moderately dark - that the issues arise. As long as I am willing to lighten things more than I want to, noise seems to vanish. I will be experimenting with LAB to see if that allows me to fix this.

So the noise thing seems soluble, but not the adjustment of tones or the banding thing. But the progress made so far makes me feel a solution will come.

Watch this space - and thanks again!

Ed

 

[ErikKaffehr]

Hi Ed,

A couple of months ago I have seen an odd banding issue on my P45+. What I have found was that it was caused by my DNG-profile generated by Adobe DNG Editor. It was also present in Capture One but went away with Adobe Standard in LR and also using a DNG profile created with DCamProf.

So, I would think camera profiles may be the basic cause of things.

Best regards
Erik

I just want to say thanks to you all for your help and advice. I have not got this licked yet, but I am making progress. I'll continue doing testing and report back when I have had the time to spend more time. But one thing is already clear - if I lighten the dark areas within a single file, they are remarkably noise free. It's trying to adjust the tonal values within those areas - especially if I want them to end up being moderately dark - that the issues arise. As long as I am willing to lighten things more than I want to, noise seems to vanish. I will be experimenting with LAB to see if that allows me to fix this.

So the noise thing seems soluble, but not the adjustment of tones or the banding thing. But the progress made so far makes me feel a solution will come.

Watch this space - and thanks again!

Ed

 

[Pradeep]

I am no expert on this issue, but on another forum there is a discussion on banding with A7R files. Some of the possibilities are

1. Incorrect profile, perhaps trying a third party Pentax profile may help
2. Try Flattening the image to see if the banding disappears.
3. Try a different RAW convertor
4.Does the banding persist when printed?

Pradeep

 

[MrSmith]

are you clipping a channel in those deep colour areas? if your rgb values are a zero in one of the channels then you will get banding/posterisation. i have had this with red products and there are various ways round it but always process out with some values in all channels and then tweak the colour in post. often the monitor cannot show the true colour and it disappears if you print. maybe try luminosity mode for your curve and then an HSB adjustment layer on top of that, or selective colour. You can also use a colour balance layer to bring back values into one channel.
i’m using these methods more and more due to curves not always giving me the results needed.
it may be a profile/processing issue so ignore the above if that proves the case.

 

[Paul2660]

Ed,

I sent you a pm, but I did want to again compliment the Sydney bridge in the morning/evening (wasn't sure) fog. Love that shot and again it shows me the direction I want to go. Really nice DR in that at iso 100.

As for banding, I worked up the PEF in LR CC 2015, then worked on it just a bit in Topaz, mainly clarity. I can't see any banding and I did look hard. It's actually a very clean show, virtually no noise, even in the lower right/left corners.

Looks like it was taken with the 25mm, sad that Pentax pulled that lens, as you have a very good copy.

I can send you both of my conversions. I did them both in Adobe RGB (1998) and Prophoto. No Problems with either. I tend to use Adobe RGB 1998 since I have much less printing gamut issues there.

Paul

 

[gazwas]

Now that is a beautiful picture!!!

_IMG0725Step4sRGBSMALL by Ed Hurst, on Flickr[/IMG]

 

[Ed Hurst]

Hey everyone,

Thanks so much for the generous help and the kind compliments on my shot. Apologies for the slow reply - not had much opportunity to be on here over the last week or so (the joys of being a parent of a 16 month old boy, while holding down a job!).

I am planning to try the following from the excellent advice above:
- Trying different profiles (though I have already tried Adobe and third party ones - so I don't expect this to make the problems go away);
- Using a different raw converter (keen for this not to be the answer, since I like ACR's workflow, but hey, if it works!);
- Using luminosity mode in curves.

In response to the points made above, the issue is apparent in prints (not just on screen), it is apparent when the file is flattened and I already use Adobe RGB colour space.

Please note that the banding and noise issues are probably separate issues - the Harbour Bridge fog shot showed noise for me but not banding. The Opera House shot showed banding but not noise. So Paul, the shot you have reprocessed (would love to see your versions, by the way, as offered - thanks so much!) showed noise for me in the bottom right hand corner, but not banding.

Paul - the fog shot was on the 55mm lens, not the 25mm, but you're so right about it being a shame it is discontinued. I love the lens (though it's not perfect).

So far, with the noise issue, I seem to be able to get rid of it by lightening the file (more than I want to), but I cannot let those areas be agreeably dark without noise appearing - even if I add the darkness back later with adjustment layers. So there is something going on here I have not yet worked out.

Thanks again everyone - you guys are amazing!