need to find a 8bit dither solution for photoshop gradient

Discussion in 'Photoshop Tutorials' started by Radim Schreiber, Aug 7, 2003.

  1. Hi,
    I need to use a 8bit mask (grayscale) for large file (10,000x5,000
    pixels). I don't get very smooth results using gradient tool, because
    dithering method is not progressive enough for this large scale (I can
    see banding). I have applied some noise, but didn't solve problem
    completely. Right now I am searching for alternative, and I thought
    something like a "Dither plug-in" for PC would help, but I cannot find
    one. I could pay for it if necessary.

    Any other ideas?

    Want to know what I am doing? Follow this link to another discussion
    group:
    http://forums.dpreview.com/forums/read.asp?forum=1014&message=5766458

    I appreciate your help,
    Radim
     
    Radim Schreiber, Aug 7, 2003
    #1
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  2. Radim Schreiber

    Toby Thain Guest

    Radim,

    I tried both RGB and Grey scale gradients from black to white. I was
    able to demonstrate by changing adjacent colour palette entries
    (consecutive channel values) that the built-in gradient dither does in
    fact blend smoothly and completely between channel increments (1/256).

    Basically I cannot duplicate your problem - I see no banding. Are you
    confusing what you see on screen - which is affected by colour
    management, frame buffer effects etc and may show spurious banding -
    and what is actually in the data (demonstrably smooth)? Or do you
    simply have gradient dither turned off?

    Toby
     
    Toby Thain, Aug 8, 2003
    #2
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  3. Toby,
    You are right, that it is difficult to see banding in grayscale.
    Actualy my problem lies in large files and also using this gradient as
    a grayscale mask in adjustement layers. If you are interested to
    duplicate my problem, follow up discussion on dpreview (link is in my
    first post), or simply get a image of blue sky (with dimensions around
    10,000x5,000 pixels) and create adjustment layer, and boost levels
    quite a bit to brighter or darker side. Than create smooth graduation
    from left to right (or circular) accross the whole image and see what
    happens.

    If you flaten your results and tweek levels to the middle (extreme,
    not practical technique), you should be getting simlar result as this
    picture:

    http://www.theskyfactory.com/temp/CST0006_01_banding.jpg

    That is a reason why I am trying to find a dither solution for
    photoshop.

    thanks for your observations,
    Radim
     
    Radim Schreiber, Aug 8, 2003
    #3
  4. Radim Schreiber

    Toby Thain Guest

    My first test proved it is not the gradient (mask) that is the
    problem. The gradient is properly dithered by Photoshop.

    In my second test, after reading your post, I was able to obtain
    visual steps - but only when the input data was poorly quantised. This
    is aggravated by application of the colour correction (especially
    extreme corrections), revealing banding or stepping (quantisation
    effects) *in the input data*.

    It's actually not Photoshop's fault - it's just bad input - so I can
    suggest no remedy other than to improve the quality of your source
    images. Scanning/shooting with better dynamic range (>8 bits per
    channel), using a different digital camera, or using a drum scanner,
    may help mitigate this.

    Toby
     
    Toby Thain, Aug 9, 2003
    #4
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