Polariser plus SLT - blotchy sky problem

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edrice
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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 3:55 pm

Greg Beetham wrote: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

Greg, you are right. Here's one from the NEX7 I did a little differently. At first I thought there might be a small dust in the upper right. But beneath it is a crop of the upper-right corner that is completely desaturated, so it looks like the same thing is going on here. (Again jpg out of camera)


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edrice
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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 4:00 pm

Greg Beetham wrote: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

Greg, yes, that's why I put the sky on a separate layer so I'm blurring that and not the rest of the image. Thanks for the links as I'm always looking for new techniques. I'll give them a thorough going-over.

Ed

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 5:16 pm

I should add I left out some steps. Looking at the Vimeo video reminded me of what you are referring to about blurring the whole image. I've done it a couple of different ways. One is to open the image and then duplicate it to make a copy and then in the copy I select the sky and then cut the inverse pixels. I'd then sample the sky as the foreground color and and fill the remainder of the cut area with that so that when the gaussian blur is applied you don't wind up with colors from the cut area mixed in. I then go back to the original image and select the sky in that one and do an inverse copy and paste it over in the duplicated image and shift-move it back down to where it belongs. There are variations of this where you could paste the whole image into th dup and then cut the sky and make sure you have layers dragged into the proper order.

This method has always seemed to work well and and the right amount of blur can maintain the gradients in the sky. I've even been able to make do with clouds in the sky with a little more care. but I'm going to look into the gradient tutorial also. Looks like it might have some possibilities.

Ed

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Wed Aug 01, 2012 6:42 pm

Here's a quick-and-dirty blurring of David's Mono sky. I wasn't that careful with the selection lines and should have expanded it a bit, but like I said, quick-and-dirty.

Ed
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Re: Polariser plus SLT - blotchy sky problem

Unread postby Greg Beetham » Thu Aug 02, 2012 11:56 am

Yes Ed that looks like it has potential if the numerous bands can be smoothed out; trouble is David has already had a bash at it too, it’s not the original file so that makes it difficult to fiddle with.
I had a dabble with it to see if I could find a filter (sky selected) that would improve things but I couldn’t find one in E8 that did anything worthwhile, there was a couple of filters that tried to do something but didn’t seem to have the necessary punch.
I thought of Corel Paintshop PhotoPro X3 but it’s a learning curve with that one as I haven’t devoted enough time to getting to know it yet, it seems to have more controls and more powerful than E8 though so maybe if the photo was processed from scratch in that program it might come up with a different result…who knows. PhotoPro works really differently to the way E8 does so I was all at sea with it. I have a lot of faith in Corel products because of Corel Draw but maybe PhotoPro needs some further work…I don’t know what to make of it in absolute terms yet, maybe I was using it incorrectly, I know there is a new edition (X4) out so maybe they’ve done some re-organising.
I originally stopped using it because I couldn’t figure out how one reduces an image for the web and still retain high enough quality not to produce weird results, at least as per what I could see in real time on screen (I think sometimes editing program/s don’t show things correctly as well, updating view glitches? File size vs. full screen thumbnail/screen resolution/translation glitches?).
Greg

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Re: Polariser plus SLT - blotchy sky problem

Unread postby johnstra » Thu Aug 02, 2012 10:08 pm

I thought I had replied already but I cannot find my post so here we go again.
I can now see the problem but it is not always present. I could not find it in the shots I took with the 28-75 and old 2 stop Hoya polariser. However I have seen it in a shot I took yesterday with the 16-80CZ and a Hoya HD. It is not as apparent as in David's shots and I am sure he is right in that we don't get those really deep blues here. I can't find the pic right now to post it but what I find is that I cannot see the fault if the sky is not sharpened. It is also worse if the colour noise reduction is set too low. I find that the default of 25 is about right for that. So in Adobe Camera Raw using Photoshop or Lightroom I use the masking slider (press ALT while sliding to see the extent of the masking). I used around 50 on my shot. This fixes it and generally you do not need to sharpen a sky. I don't know if that will work in your cases but it's worth a try.
Bob Johnston

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Fri Aug 03, 2012 4:39 pm

Greg Beetham wrote:Yes Ed that looks like it has potential if the numerous bands can be smoothed out; trouble is David has already had a bash at it too, it’s not the original file so that makes it difficult to fiddle with.

Greg, I'm not seeing the bands while in photoshop and wonder if, in addition to stripping out the metadata, save-for-web compresses the file enough to create the banding in the sky. I usually don't do save-for-web that much because I rarely need to get the file size small enough to meet the maximum upload requirements on clubalpha. I'll have to look more closely and see if there are settings that can be made in save-for-web that give more control over this.

Ed

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Re: Polariser plus SLT - blotchy sky problem

Unread postby kuau » Wed Aug 22, 2012 2:26 am

I would just add that using a polarizer on anything wider then a 35mm lens is going to be problematic.
Uneven blue sky is very common when using a polarizer with a wa lens.
Also a very good tip bellow if you use LR or ACR, use the masking in the sharpening with the alt key pressed down until the sky goes black, so the sharpening will not be applied to the sky. I do this all the time.
Another tip, or something worth trying is on the A77 shoot at ISO 50 and see if the sky looks any cleaner.

Steven

johnstra wrote:I thought I had replied already but I cannot find my post so here we go again.
I can now see the problem but it is not always present. I could not find it in the shots I took with the 28-75 and old 2 stop Hoya polariser. However I have seen it in a shot I took yesterday with the 16-80CZ and a Hoya HD. It is not as apparent as in David's shots and I am sure he is right in that we don't get those really deep blues here. I can't find the pic right now to post it but what I find is that I cannot see the fault if the sky is not sharpened. It is also worse if the colour noise reduction is set too low. I find that the default of 25 is about right for that. So in Adobe Camera Raw using Photoshop or Lightroom I use the masking slider (press ALT while sliding to see the extent of the masking). I used around 50 on my shot. This fixes it and generally you do not need to sharpen a sky. I don't know if that will work in your cases but it's worth a try.

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Re: Polariser plus SLT - blotchy sky problem

Unread postby John David Cubit » Sat Sep 15, 2012 10:28 pm

Since I'm planning to buy the a99 as my first SLT camera, I'm disappointed to hear that the SLT hardware may not work well with polarizers. Because of the uneven effect on blue skies and reduction in light, I usually avoid these filters. I can do the skies better in post processing. However, the filters are very effective in controlling unwanted glare from water surfaces and shiny leaves, which cannot be fixed in post processing. For example, no amount of PhotoShop fixes will show the inhabitants of a tidepool that were obscured by reflections off the surface of the water.

(By the way, Peter, there are slim polarizers and ones with expanded rings that will eliminate or reduce the vignetting you illustrate.)

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Sat Sep 15, 2012 11:07 pm

John David Cubit wrote:Since I'm planning to buy the a99 as my first SLT camera, I'm disappointed to hear that the SLT hardware may not work well with polarizers. Because of the uneven effect on blue skies and reduction in light, I usually avoid these filters. I can do the skies better in post processing. However, the filters are very effective in controlling unwanted glare from water surfaces and shiny leaves, which cannot be fixed in post processing. For example, no amount of PhotoShop fixes will show the inhabitants of a tidepool that were obscured by reflections off the surface of the water.


And water and leaves are some of the main reasons I use polarizers, not just skies.

But my example above shows that the NEX-7 produces the same problem, so it's not limited to just SLTs.

Ed

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Re: Polariser plus SLT - blotchy sky problem

Unread postby David Kilpatrick » Tue Sep 18, 2012 12:16 am

I may have some kind of resolution to this. It appears that lo-pass filter assemblies - as I have suspected but not been able tp confirm - polarize light, as any thin-film diffraction based filter will do. They also consist of two or more layers or differential offset and correction coatings.

It is more likely that lo-pass (AA) filter inconsistency is responsible for variations in polarized tones such as sky, than the SLT mirror. Both have potential polarizing effects.

Based on this, I'd go for for a sensor entirely free of any optical layer between it and the lens. Even the Nikon D800E, it seems, has a form of AA filter. To get what I want, it's Leica, Pentax or medium format.

David

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Tue Sep 18, 2012 12:39 am

I even see it in the RX100. (colors exaggerated)

rx100.jpg
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Re: Polariser plus SLT - blotchy sky problem

Unread postby Greg Beetham » Tue Sep 18, 2012 12:49 am

How was the RX100 image processed Ed? (or not)
Greg

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Re: Polariser plus SLT - blotchy sky problem

Unread postby Dusty » Tue Sep 18, 2012 1:43 am

David Kilpatrick wrote:Based on this, I'd go for for a sensor entirely free of any optical layer between it and the lens. Even the Nikon D800E, it seems, has a form of AA filter. To get what I want, it's Leica, Pentax or medium format.

David


Pentax? I thought about them, as they have IBIS, but then Barry noted the problem with white balance and exposure. I'm also a bit worried about their sticking around in today's market as a DSLR system. The other 2 choices I can't afford!

Dusty
An a700 and couple of a580s, plus even more lenses.

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Re: Polariser plus SLT - blotchy sky problem

Unread postby edrice » Tue Sep 18, 2012 2:00 am

Greg Beetham wrote:How was the RX100 image processed Ed? (or not)
Greg

It's a jpg that I just ramped up the vibrance, saturation and contrast to make it stand out. That was all. Just looking at the shot before doing any of that, it looks fine.

I picked up one of those Lensmate filter adapters. They just became available last week.

Ed


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