Polariser plus SLT - blotchy sky problem

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dewarp
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Re: Polariser plus SLT - blotchy sky problem

Unread postby dewarp » Thu Jul 19, 2012 11:52 am

Hi Greg

Yes, the blocks at the top are clearly visible. However, when I take a full sized TIFF and look at it in PS x 400% there is no sign of the blocks - just the normal "blanket" look. I think the blocks came with the jpg conversion.

regards - Peter

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Greg Beetham
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Re: Polariser plus SLT - blotchy sky problem

Unread postby Greg Beetham » Thu Jul 19, 2012 3:35 pm

Yes Hi Peter, it’s so badly broken up where the most polarization is its hard too believe it’s just the program JPEG reduction algorithm that’s fowling things up to that degree, but if the TIFF is good it must be I guess. I wonder if the camera produced JPEG is any better when a polarizer is used?
And another question is is the A900 any different with a polarizer, is its JPEG's any better? (I've never heard of anyone complaining though)
Greg

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Re: Polariser plus SLT - blotchy sky problem

Unread postby David Kilpatrick » Thu Jul 19, 2012 5:37 pm

This is one of the polarised sky shots (a 100% clip from an ISO 100 Alpha 77 shot) processed about as well as I could to reduce the patchy effect:
polarizedsky.jpg
polarizedsky.jpg (302.35 KiB) Viewed 3021 times

Obviously, it's seen in isolation, it just looks too uneven to be acceptable - and this is the best I can do.

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Re: Polariser plus SLT - blotchy sky problem

Unread postby Greg Beetham » Thu Jul 19, 2012 5:57 pm

It looks like violet/blue coloured water dribbling down a window, its pretty faint on my screen at first but the more you look the more you see, it probably looks a lot better at normal size.
Greg
Ps I still wonder how a camera JPEG would look, the same or different?

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Re: Polariser plus SLT - blotchy sky problem

Unread postby Dr. Harout » Wed Jul 25, 2012 10:19 pm

Checked many photos made with a77 with either 70-300 G or 2/24 ZA with respectively Hoya Ultra whatever and Zeiss T* polarizers. No blotchy skies!
A99 + a7rII + Sony, Zeiss, Minolta, Rokinon and M42 lenses

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Re: Polariser plus SLT - blotchy sky problem

Unread postby johnstra » Mon Jul 30, 2012 10:08 pm

Sorry for the late post but life caught up with me a bit. I have my A77 back from repair and have tried an old fashioned 2 stop Hoya on my KM 28-75. I cannot find any evidence of the blotchy sky effect at all. I now have my SAL16-80 back too. I have been recovering from a minor operation so I have missed the recent sun but I will try the A77, 16-80 combo with a more modern Hoya HD polariser tomorrow, weather permitting.
Regards,

Bob
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Re: Polariser plus SLT - blotchy sky problem

Unread postby David Kilpatrick » Tue Jul 31, 2012 12:04 am

Remember, I was talking about intense deep blue California sky over Sierra rocks - the sort of polariser blue you never get in Britain!

My paler skies are not a problem.

David

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 3:08 am

Yeah, I think I'm seeing evidence of this with the A65.

I live in southern California about 3 hours south of the Sierras and when I saw the thread I had to go digging arounnd to see if I could find anything that matched the circumstances. This shot is from high up in our local mountains and I was using the A65 with the CZ16-80 and a Hoya HMC polarizer. A polarizer in this area is a most important piece of equipment. I might as well leave the camera at home if I leave the polarizer. Here's one I found, the full shot and then number two is the upper-right over the tank. Number three is upper-left. This is jpg straight out of the camera.

fullshot.jpg
fullshot.jpg (42.39 KiB) Viewed 2784 times


overtank.jpg
overtank.jpg (62.29 KiB) Viewed 2784 times


left.jpg
left.jpg (63.9 KiB) Viewed 2784 times


Usually I would have more shots like this but I've been using the NEX7 so much that the A65 is feeling lonely. I guess I need to take a closer look at some of those.

Ed
Last edited by edrice on Wed Aug 01, 2012 3:16 am, edited 1 time in total.

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 3:13 am

Here's one from the raw of the same shot and crop above from over the tank. I didn't match the colors exactly to the jpg. It may be a bit less here, but I think I still see it. Am I just gone bats seeing things now?


fromraw.jpg
fromraw.jpg (80.9 KiB) Viewed 2786 times

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Re: Polariser plus SLT - blotchy sky problem

Unread postby David Kilpatrick » Wed Aug 01, 2012 1:33 pm

Got to admit that looks very even, but unfortunately the noise level would result in a possible problem for our end uses of our images - Alamy, and even more so if we were to try placing image on iStock and other sites whose licencing model I don't agree with.

Here's a typical Californiia trip polarised sky - Mono Lake - on A77 at ISO 100 - I reduced this to 3600 pixels wide final file, as I was not happy with the detail sharpness (nothing to do with the camera or lens, entirely to do with the temperature and the heat haze - I have had to discard plenty of shots entirely, and reduce others to minimum acceptable size, because of heat haze issues on this trip).

monolake-polsky.jpg
monolake-polsky.jpg (416.47 KiB) Viewed 2751 times

As you can see, it's a very dense sky when polarised.

Here is a 100% clip showing the kind of uneven quality I get and maybe it's also down to colour noise reduction:

polarizedsky-2.jpg
polarizedsky-2.jpg (54.58 KiB) Viewed 2751 times

I don't like getting this kind of result as it is very difficult to correct in any way. It is just acceptable but only just for commercial use. It is also possible that the Hoya £100+ top end polariser is not very even. I know that many of my expensive earlier ones, including Minolta, are patchy when examined carefully.

David

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Re: Polariser plus SLT - blotchy sky problem

Unread postby Greg Beetham » Wed Aug 01, 2012 2:41 pm

David there is a very ragged edge horizontally about half way up the sky especially on the left side of the seascape image, there are a couple of other ragged edges but that one is most noticeable.

Ed if you want too see something horrible just get the crop with the tank still in it and do nothing else but boost the saturation +10 or even +15 i.e. not much and watch what happens. (I’ve already done it) :shock:
Greg

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 2:49 pm

What I've tended to do in the past with blotchy skies, and in particular grainy skies from film scans, is to put the sky on a separate layer and give it a good dose of gaussian blur and ended up with the smoothest skies you could ever ask for. I don't know if Alamy accept such file workage. Tihs works for cloudless skies which we get a lot of here.

Is that color banding that I see in the sky gradation on the left going up from the distant hills to the darker upper sky?

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Re: Polariser plus SLT - blotchy sky problem

Unread postby Greg Beetham » Wed Aug 01, 2012 3:29 pm

I still think it’s more to do with bad program file processing/reduction, a large file with a gamma effect sky not being reduced in the processing and size reduction with even gradient where there should be an even gradient. I’ve noticed sky artefacts in some skies from my A100 and A700 not even using a polarizer but much less so with the KM5D so I was putting it down to the size of the file to begin with, i.e. the larger the file the more it has to be reduced and the more pronounced the artefacts…sometimes, and one method I used to minimize them was to increase the file size with the quality slider, the more it is boosted (while keeping the 1000 pixel limit) the more the artefacts diminish, it doesn’t get rid of them completely but it sure helps.
Ed I thought Gaussian blur would soften the whole image but I see there is a technique for using it for gradient smoothing in this discussion, http://slodive.com/photoshop/how-to-correct-banding-in-your-gradients-using-photoshop it got a bit involved for my three working brain cells, this next tutorial I haven’t looked at yet but it might be promising too. http://vimeo.com/4569340
Greg

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 3:29 pm

edrice wrote:What I've tended to do in the past with blotchy skies, and in particular grainy skies from film scans, is to put the sky on a separate layer and give it a good dose of gaussian blur and ended up with the smoothest skies you could ever ask for.

An example from a 35mm slide taken with the X700. The first shot is the faded original with what looks like faulty processing with the vertical stripe in the sky. and the second is the corrected sky and restored colors.


before.jpg
before.jpg (191.42 KiB) Viewed 2740 times


desertdoggies1.jpg
desertdoggies1.jpg (237.67 KiB) Viewed 2740 times


The colors may look a little oversaturated in the second one. Funny, it doesn't look that way in Bridge. I didn't do a save for web on that one and may have something to do with it. But you get the idea.

Ed

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Re: Polariser plus SLT - blotchy sky problem

Unread postby Greg Beetham » Wed Aug 01, 2012 3:48 pm

I've sort of tentatively come to the conclusion that scanners use too much contrast when producing a photo image file from a negative, I re-worked a couple of scanned negatives (TIFFS of old portraits taken with the Bronica) in Elements trying to work out a way of fixing all the small processing spots and harsh grain (none of which are visible in a wet print) and one thing I found was the big improvement that occurred when moving the contrast slider a long way into the minus area. There is probably a filter that would work also, I remember fooling around with various filters the other day and found one that seemed to smooth things quite nicely (not Gaussian) but now I can’t remember which one it was. I’m pretty sure it was in the Elements Menu bar…Filters>Adjustments>?
Greg


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