Skip navigation
Currently Being Moderated

Banding at magnification lower than 64%

Mar 24, 2013 1:52 PM


Seriously I cant figure this out. When I'm viewing photo at zoom lower than 64% banding kicks in. At zoom higher than 63% everything smoothed out. It's giving me a hard time when I'm trying to retouch big files at lower magnification because actually I cant know until I zoom in do I'm removing something what exist or actually not!


I know it's an issue regards do displaying preview of 16bit image as 8bit image. I was checking this in many ways and it appears only in 16bit mode. I'm quite a quality maniac so I always retouch in 16bit mode and ProPhoto color space to give myself a bit more room to play with post production.


Please take a look at snaps made using windows snipping tool. All images are in ProPhoto color space but I also have tried this in RGB and it looks quite the same.


1. With banding.

16bit mode

ProPhoto color space

Zoom: 63%

https://dl.dropbox.com/u/2234179/1banding.PNG

1. Without banding.

16bit mode

ProPhoto color space

Zoom: 64%

https://dl.dropbox.com/u/2234179/1bandingno.PNG


Can you guys let me know is it normal, does everybody suffers the way I am? If not how to fix it?


I'm on windows 7 ultimate 64bit, 64GB memory, Intel I7 processor, geforec GTX680 GPU.


Thnx.

 
Replies
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 24, 2013 3:23 PM   in reply to LeoNeon51

    You have a good eye.

     

    1.  Photoshop composites layers using a speed-optimized process on downsized 8 bit data for zoomed-out resolutions when the Cache Levels setting is 2 or higher in the Performance preferences.  Thus, at zoomed out sizes you see posterization.  You can force an egregious level of it with a couple of extreme curves operations.  A workaround, which comes with downsides, is to set your Cache Levels preference to 1, which forces all compositing to be done at full resolution.  This does work, and I use it when I do astrophotography processing myself, because I often use extreme Curves operations, but the downsides are 1) that it slows things down (maybe not a problem if you have a rompin' stompin' computer), and 2) that it may destabilize Photoshop and require you to work with the Basic drawing mode.

     

    2.  There is a long-standing bug in the color-management logic that Adobe runs in the GPU in Normal and Advanced modes, which gives rise to the slightly colored banding you see.  Adobe has known about this since way back, and as you have correctly shown, the problem does not exist in the Adobe Color Engine that runs in the CPU, which is what Basic mode causes.

     

    Since the CPU does more work that would normally be done in the GPU when you configure Basic mode, it may change the performance you see.  However, it's not bad and can represent a good workaround if the accuracy of what you see on your screen is highly important to you.

     

    -Noel

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 24, 2013 3:32 PM   in reply to LeoNeon51

    By the way just for clarity, OpenCL is not the same as OpenGL.  OpenCL is not involved in this.

     

    The key for the ProPhoto RGB workaround is that the color-management not be done in the GPU, but rather in the CPU, and using either Basic mode or disabling the use of the GPU entirely is what makes that happen.

     

    And it's also worth noting that these are both problems with the DISPLAY of your image in Photoshop while editing - they do NOT cause inaccuracies in the image itself, unless you're doing screenshots (which of course would be data that's been through Photoshop's color-management).

     

    -Noel

     
    |
    Mark as:
  • Currently Being Moderated
    Mar 24, 2013 5:06 PM   in reply to LeoNeon51

    LeoNeon51 wrote:

     

    Even if I disable OpenCl

     

    As Noel said, OpenCL has nothing to do with this.

     

    Go into the Advanced Settings for the graphics processor, found in Preferences > Performance, and set it to "Basic".

     

     

    and set cache levels to 1 it's steel happening. Problem appears in ProPhoto but as well in RGB (a bit less but steel). Your work around seems not working for me, is there any other?

     

    In addition to using Cache Levels of 1, or even if you use more cache levels, try a low-level noise layer at top of stack. It can be made not visible when not required, such as when generating a file for print.

    To make a noise layer...

     

    Create a new top layer with Overlay blending mode and fill it with 50% gray.

     

    If you use the New Layer dialog then never do a 16 bpc 50% gray fill with it because that creates RGB (16448, 16448, 16448) instead of the correct RGB (16384, 16384, 16384).

     

    Edit > Fill command is one way to get the correct 50% gray fill.

     

    Use Add Noise filter to add 25% uniform monochrome noise to the new layer.

     

    Reduce the new layer's opacity to about 5% then lock the layer so it cannot be accidentally disturbed. Remember, the layer should have Overlay blending mode.

     
    |
    Mark as:
  • Currently Being Moderated
    Mar 24, 2013 5:40 PM   in reply to LeoNeon51

    Screen-shot-2013-03-25-at-00.33.25.png

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 24, 2013 6:44 PM   in reply to LeoNeon51

    You need to restart Photoshop after making the settings changes, or you will not be testing what you think you're testing.

     

    -Noel

     
    |
    Mark as:
  • Currently Being Moderated
    Mar 24, 2013 7:50 PM   in reply to LeoNeon51

    The noise layer doesn't help hide display banding when zoom is below 64% unless Cache Levels is 1. Are you absolutely sure that you set CL to 1 then relaunched Ps before testing the noise?

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 25, 2013 7:27 AM   in reply to LeoNeon51

    It's worth noting that the bike images you're posting are nearly black (the levels are in the single digits).

     

    If you're seeing posterization in them directly, without enhancement (e.g., via a Curves layer), could it be that your monitor is well out of calibration, and you're just seeing more in the shadows than you should be seeing?

     

    -Noel

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 25, 2013 9:10 AM   in reply to LeoNeon51

    Sounds like your monitor is displaying the lowest luminance levels brighter than most - usually folks don't start seeing a difference until level 4 or 5; many can't see any squares in the first fow at all.  That your system is more sensitive to level changes at small values than most probably says your gamma response is a bit on the high side. 

     

    However, that still doesn't seem to describe why you should see a lower quality compositing of layers at zoomed-out resolutions.

     

    It could be a color-management issue somehow I guess...  Monitor color profiles have been known to be faulty.  Using the Windows Color-Management dialog, Devices tab, what profile is associated with your monitor?  Does anything different happen if you add the sRGB IEC61966-2.1 profile to the list and make it the default for your monitor?

     

    I have not seen, with Cache Levels 1, Photoshop show a difference in compositing quality between zoomed-out and 100% resolutions, but that doesn't mean it can't happen.  It may be specific to individual video drivers, and more complex under the covers than any of us give it credit for.

     

    -Noel

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 25, 2013 1:47 PM   in reply to LeoNeon51

    It's using the default sRGB IEC61966-2.1 profile already then, so that's probably not the issue.

     

    With my monitor calibration I can (barely) make out the level 1 square, and the level 2 square is just slightly more visible.  I don't sense a distracting level of banding in the images you posted up above unless I enhance your images quite a bit.

     

    If display accuracy is that critical to you, perhaps you might want to investigate what it would take to get 30 bit color (that's an extra 2 bits each for red, green, and blue).  With a full 30 bit signal path (i.e., where video card, cable, and monitor are capable of 30 bit color and the Photoshop 30 bit color setting enabled) the number of discrete levels of gray available goes from 256 to 1024.  I doubt you'd be able to sense those transitions.

     

    I just remembered something I had forgotten about...  As I recall the 13.1 Photoshop release had a bug in at least some of the color-management logic that could cause a slight inaccuracy and 2 level output jumps in what should be single level changes, effectively reducing your color capablity to 7 bits per color.  I wonder if you could be seeing that...  If you download this 16 bits/channel smooth gradient test file and load it into Photoshop, do you see evenly spaced level changes from center to edge?

     

    http://Noel.ProDigitalSoftware.com/temp/DarkGrayGradientTestImage.psd

     

    -Noel

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 25, 2013 4:10 PM   in reply to LeoNeon51
     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 25, 2013 5:42 PM   in reply to LeoNeon51

    I think we've nailed down the problem.  I don't know if it's a software issue or a hardware issue on your system, but the best possible performance would be where your system would display every single step with an equal jump in brightness, and there would be no appearance of grouping - the gradient would just be even all the way from corner to edge (I see it that way).  Where you see the groups divided up by what look like bigger steps, it's because there is a 2 level grayscale jump instead of a 1 level jump.

     

    My system displays that gradient all in one smooth transition, with 1 level jumps at every transition.

     

    Capture your screen showing that gradient, please, save it as a PNG, and post it here.  I will be able to tell you, by looking for 2 level jumps in your screen grab, whether the problem is occurring in the software or at your video card and monitor.

     

    I'm not that familiar with the settings in nVidia drivers, but as I recall there's a section for adjusting desktop color settings.  Have you changed any of the color controls there?

     

    -Noel

     
    |
    Mark as:
  • Currently Being Moderated
    Mar 26, 2013 10:39 AM   in reply to LeoNeon51

    There is no 2-level jump in your screenshot.

     

    I'm puzzled by your sudden appearance of banding when zooming at 63.75% or lower when Cache Levels is 1.

     

    Please do the following:

     

    Set Cache Levels to 1

    Set GPU mode to Basic (which shouldn't matter with sRGB, but do it anyway)

    Relaunch Photoshop

    Open the test gradient image

    Add a Curves Adjustment Layer with "Lighter" preset

    Zoom to 64%

    Grab screenshot

    Zoom to 63%

    Grab screenshot

    Post both screenshots

     

     

    My screenshots below show highly obvious banding appear at zoom 63% when Cache Levels is 4, but not when CL is 1.

     

     

    cl1-64.png

     

    cl1-63.png

     

    cl4-64.png

     

    cl4-63.png

     

     

    In the distinctively banded screenshot, there is the same quantity of bands as the other screenshots, each band being 1 level different from its neighbours. However, each 4th or 5th band is so narrow that the appearance is very similar to a gradient with fewer steps and with level jumps of  1-2-1-1-1-2-1-1-2-1-1-1-2-1-1-2-1-1-……..

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 26, 2013 12:15 PM   in reply to conroy

    I agree that there are not multi-level jumps in LeoNeon51's screen grab, which says that digitally the data is clean.

     

    Seems to me we have potentially two issues here that conpsire to make the banding visible.

     

    1.  The 8 bit lower-quality compositing that occurs with cache levels > 1 at zoomed-out magnifications.

     

    2.  An issue where the monitor signal is being quantized between the video card and monitor somewhere.

     

    LeoNeon51, do you have the 30 bit color setting enabled?  It's possible that might help, as it instructs the video card to do higher accuracy work.  But that's dependent on specific hardware and driver capabilities.

     

    EDIT:  I just saw the response you submitted while I was typing, LeoNeon51.  Try the 30 bit color setting.

     

    Also, how do you have your video card cabled to your monitor?  Different signal paths have different characteristics, and you may have capabilities you're specifically not taking advantage of.

     

    -Noel

     
    |
    Mark as:
  • Currently Being Moderated
    Mar 26, 2013 12:33 PM   in reply to LeoNeon51

    OK, your screenshots make it clear that something is peculiar about your system.

     

    You are correctly getting good gradients when zoom is 64% regardless of Cache Levels setting, and correctly getting a poor gradient when zoom is 63% and Cache Levels is 4.

     

    You are incorrectly getting the poor gradient when zoom is 63% and Cache Levels is 1. The failure of CL 1 to be effective in your system explains your frustration with the bike image and the failure of a noise layer to hide display banding when zoomed out.

     
    |
    Mark as:
  • Currently Being Moderated
    Mar 26, 2013 12:28 PM   in reply to Noel Carboni

    Noel Carboni wrote:

     

    The 8 bit lower-quality compositing that occurs with cache levels > 1 at zoomed-out magnifications.

     

     

    Yes, something is definitely wrong when Cache Levels 1 is failing to give LeoNeon51 full-quality compositing when zoom is 63.75% or lower.

     
    |
    Mark as:
  • Currently Being Moderated
    Mar 26, 2013 1:25 PM   in reply to LeoNeon51

    Yes, 32-bit mode always uses full-quality compositing as far as I've noticed, but a great many tools, adjustments and filters are unavailable in that mode.

     
    |
    Mark as:
  • Noel Carboni
    23,526 posts
    Dec 23, 2006
    Currently Being Moderated
    Mar 26, 2013 4:48 PM   in reply to LeoNeon51

    I'm not familiar with your particular hardware, but my current theory is that your video card and monitor, to achieve the calibration you desire, is limiting the range of signals to a set smaller than the maximum possible range from 0 to 255 for each of the three colors, so some levels simply cannot be displayed.  In short, you're getting slightly less than 24 bit color.  This causes 2 level jumps between certain adjacent colors. 

     

    This alone might be tolerable, but in addition, some part of the color-managment logic within your setup is also conspiring to cause 2 level jumps between certain colors, and possibly these are combining so that you see a 3 level jump in certain cases.

     

    That said, I have Dell monitors (older ones) connected via DVI and I don't see any multiple level jumps in a gradient that runs all the way from black to white - and I do use my display driver settings to calibrate.  This might be a difference between ATI and nVidia, or just the particular choices we've made in hardware.

     

    Did you see the problem before changing the display driver calibration settings?

     

    Just to be certain your system is using the sRGB IEC61966-2.1 profile, you could try adding it and making it the default in the Devices tab of your OS color-management dialog.

     

    Do you have the ability to connect the monitor to the video card by DisplayPort or HDMI?  It might be worth seeing if that uncovers more capability than DVI.

     

    I assume you tried the 30 bit color setting (making sure to restart Photoshop after setting it) and saw no improvement.

     

    -Noel

     
    |
    Mark as:
  • Currently Being Moderated
    Apr 21, 2013 2:08 PM   in reply to conroy

    Leo, in case you return to this thread, your failure to get Cache Levels 1 behaviour despite the setting in Preferences could be explained by the following quote from thread http://forums.adobe.com/message/5255798?tstart=0#5255798

     

     

    Chris Cox wrote:

     

    There is a bug with the cache level preferences on Windows.

    Try changing it in the 32 bit app, then quit and relaunch the 64 bit app.

     

     
    |
    Mark as:

More Like This

  • Retrieving data ...

Bookmarked By (0)

Answers + Points = Status

  • 10 points awarded for Correct Answers
  • 5 points awarded for Helpful Answers
  • 10,000+ points
  • 1,001-10,000 points
  • 501-1,000 points
  • 5-500 points