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Thread: Problem with stair stepping/jaggies/pixelation

  1. #1

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    Problem with stair stepping/jaggies/pixelation

    Hi, Neil again,

    I have two questions for the forum this time concerning stair stepping or pixelation.

    I shot this image using a 5dii and a 135mm 2.8 @ f11. At the time I was concentrating on focus stacking and didn't pay much attention to the pixelation on the arms of the sunglasses. Now the setup is tidied away and I think I have to reshoot...

    So, I'd love to know what went wrong and how to avoid the stair stepping pixelation again. I think I read somewhere about the ant-aliasing filter on the Canon's sensor being arranged horizontally. I shot this picture vertically. Btw, the pixelation is present in the Raw files, it's not a resampling issue. I think you should also know I shot it in sRGB and processed as a 16 bit tif.

    Secondly, is there a Photoshop method for removing the stair stepping?

    Thanks in advance, Neil.

    2013-11-12-19.09.16 ZS DMap.jpg

    Screen Shot 2013-11-16 at 19.50.51.png

  2. #2

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    Re: Problem with stair stepping/jaggies/pixelation

    It's a very dramatic image!

    If you hadn't mentioned that the issue is present in the RAW file, I would have sworn that the issue is the moire effect that is produced only at certain display sizes of whatever size you uploaded. I'm stumped and am eager to learn from others what would cause this and how to prevent it.
    Last edited by Mike Buckley; 20th November 2013 at 11:36 AM.

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    Black Pearl's Avatar
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    Re: Problem with stair stepping/jaggies/pixelation

    I came across a similar problem, oddly enought while photographig sunglasses.
    My issue was the Bowens flash heads were outputting slightly different exposures each time they fired - in usual situation this hadn't been an issue. Swapping to better quality Elincrom heads sorted it as their output was rock solid over hundreds of fires.

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    Re: Problem with stair stepping/jaggies/pixelation

    Hi Neil,

    Im no expert but here's my two bobs worth,you mentioned stacking,could it be your stacking software?
    When i tried stacking just the other day Helicon Focus told me there was a difference in my lighting? I think i was to eager to see the end result i never did any p.p first. After working on exposure on 1 image then doing a sync with rest problem sorted!

    Cheers David

  5. #5

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    Re: Problem with stair stepping/jaggies/pixelation

    Thanks guys. It's not the Zerene software, I contacted them about it to ask.

    I'm reshooting it right now with a fixed focal in horizontal crop. The stair stepping is gone... I'm using the same lights as before: Profoto & Elinchrom. The web suggested it was a contrast issue, the background is so dark against the highlight on the arms of the glasses.

    I'm eager to read what others think later. Thanks all for posting. I thought my camera was misbehaving!

  6. #6

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    Re: Problem with stair stepping/jaggies/pixelation

    It's not really clear to me if this is a stacked image, but I will assume that it is and , that it is stacked in PS.
    It is not often that the stacking sequence is an "apply it and forget it" scenario...going back to the virgin images and cutting out a fresh selection and pasting it into the offending spot in your finished image is a common necessity. In this case, as you say that the problem exists in the RAW image, that suggestion might not work anyway and a reshoot may be your only option, short of cloning from another unsullied portion of the image.

  7. #7
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    Re: Problem with stair stepping/jaggies/pixelation

    I'd also be curious to know more.

    I use Zerene all the time and have never seen this.

    I was puzzled by this:

    Btw, the pixelation is present in the Raw files, it's not a resampling issue. I think you should also know I shot it in sRGB and processed as a 16 bit tif.
    First, if you are shooting raw, it makes no difference whether you had the camera set to sRGB. It has no effect on the raw file. Second, if it is present in the raw file, it can't be from stacking, since your stacking software doesn't (AFAIK) accept raw input, and you used 16-bit TIFFs for this (as I do). Do you mean that when you opened a single raw file before editing, the pixelation was present?

  8. #8

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    Re: Problem with stair stepping/jaggies/pixelation

    Yes DanK, the original raws have the stair stepping, although not as pronounced. I use Capture One Pro for my processing. Perhaps the default sharpening exaggerated it...

    Problem with stair stepping/jaggies/pixelation

  9. #9

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    Re: Problem with stair stepping/jaggies/pixelation

    Hi everyone,

    I seem to have resolved the issue!

    Rik at Zerene systems, who make Zerene Stacker, has given me invaluable insight to my approach - even shooting tips. He has very kindly agreed to allow me post his email response here so we can all understand what might have gone wrong.

    Here it is:

    Neil, thanks for pointing me to this thread.

    For those who don't know me, I'm the fellow who wrote & supports Zerene Stacker. Lots of interesting issues come in as support requests, and Neil's problem turned out to be one of those. We exchanged quite a bit of email, and he thought other readers of this thread might be interested in what we figured out. .

    First, it quickly became evident that most of the problem was not due to stacking. I asked to see 100% crops of source files and stacked output, and the stairstepping turned out to be quite similar in both. It wasn't identical, because in order to properly align multiple source files ZS had to slightly resize the best focused image by about 1% change. Resizing always means resampling, which definitely can introduce Moire and make pixelation worse, but it didn't seem to be a big contributor here.

    I discussed the problem further with one of my colleagues. He too was initially puzzled by why the pixelation was much more obvious in Neil's images than what we're used to seeing. After quite a bit of back and forth discussion, we concluded that the problem was probably caused by a combination of three things:

    1. The rim lighting and subject shape combined to produce a very thin hard bright line.

    2. Neil's premium lens produces a very sharp optical image. Used at f/11 on a 5D Mark II, I'm quite confident that the lens is outresolving the sensor.

    3. The image appears to have been significantly sharpened, probably in the raw-to-TIFF conversion process. In fact around the bright rimline, there is an obvious black halo that suggests oversharpening.

    The combination of these three aspects ended up producing a nearly straight, very narrow, high contrast bright line. In many places the bright line produced by the rimlight is only a single pixel wide -- dark/bright/dark. -- and that's in the original source files that have over 5 times the resolution of the web-resolution image that Neil showed at the top of this thread.

    When such a line is also just a bit off horizontal or vertical, this becomes absolutely the worst case for producing visible pixelation.

    Our suggestion based on those observations would have been that Neil try reshooting using a softer rimlight, and take care to avoid strong sharpening along those long straight lines. Frequently a better overall effect can be produced by selectively sharpening areas that contain small details, while leaving long straight lines in their original softer versions. This provides the desired impression of sharpness while minimizing opportunities for pixelation to intrude.

    However there were some delays in email, and in the meantime Neil had done the followup research and shooting he describes above.

    As Neil describes, the situation improved a lot when he reshot horizontally with a different lens.

    My guess is that the improvement did not have much to do with the orientation of the camera's antialiasing filter. As far as I know, those filters are designed to be symmetric in X and Y, although it would not be surprising if there are minor differences due to manufacturing tolerances. (http://www.maxmax.com/olpf_study.htm documents the OLPF for the 5D MK II and makes a point that it's actually composed of two identical layers aligned orthogonally.) I shot some test images with my Canon T1i to check the issue. On my camera there does seem to be a bit of difference in contrast for horizontal versus vertical lines, but to my eye the amount of visible stairstepping is quite similar in both orientations. A different camera could be different, of course. It's also conceivable that there's X-Y asymmetry in some particular raw conversion software, though as a software developer I confess I'd be surprised by that.

    Instead, I suspect that more improvement was made by slight differences in the lighting and lens. Anything that would broaden and soften those problematic long thin bright lines would help a lot to reduce the pixelation.

    I hope this is helpful!

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