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    Flicker removal in Shake
    #1
    Junior Member
    Join Date
    Dec 2010
    Posts
    13
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    Hi Folks, do any of you Gurus out there know how to remove the flicker/Auto Exposre variations in Apples Shake. I had to leave the camera in auto for various reasons ie it was in a remote heli and want to even out the exposure variations in post.
    So far I have blured out the image, and applied a pixel analise node... and now I am stuck.
    I need to apply the analised date to and exposure node I think but don't know how.
    Any Ideas Guys? Many thanks ;-)


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    #2
    Member
    Join Date
    Feb 2004
    Location
    Brussels, Belgium
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    69
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    I prefer using Furnace's Deflicker tool, but you can achieve reasonably good results with a pixel analyser node as well.

    Examples are quite easy to find though... This one is directly copied from Shake's user manual...

    "The following examples show how you can use the PixelAnalyzer node to obtain image
    data that is used to correct the exposure of a shot that dynamically brightens or
    darkens. The goal is to even the exposure of the image out so it doesn’t change. These
    examples illustrate the power of expressions in Shake to automate complex operations.


    Setting Up the PixelAnalyzer Node
    Attach a PixelAnalyzer node to the problem image. It will eventually be used as a source
    of color values by expressions placed within the parameters of color-correction nodes.
    The color-correction nodes are not attached to the PixelAnalyzer node; instead, they’re
    branched off of the source image. Three different examples show three different color-
    correction nodes in use—different situations may require different approaches,
    depending on the image.

    Note: To accurately analyze changes in brightness, the PixelAnalyzer node’s analysis
    area should be positioned over the brightest area of the image.

    Method 1: Using an Add Node

    Attach an Add node to the image, then enter the following expression into its red,
    green, and blue channels:
    (PixelAnalyzer1.area1AverageRed@@1)-PixelAnalyzer1.area1AverageRed
    (PixelAnalyzer1.area1AverageGreen@@1)-PixelAnalyzer1.area1AverageGreen
    (PixelAnalyzer1.area1AverageBlue@@1)-PixelAnalyzer1.area1AverageBlue

    The first part of the expression takes the first frame of the image as the base value
    (specified by @@1). The average channel values from all other frames are compared to
    frame 1. For every frame, the current channel value is subtracted from that of frame 1.
    For example, if at frame 1 the average red value is .5, and at frame 10 the average red
    value is .6, the above expression subtracts .1 from frame 10 to arrive at .5 again.
    Note: To avoid problems when analyzing images with a lot of noise or grain, use the
    PixelAnalyzer node’s Average value parameters.
    In one possible scenario, examining the resulting image with the PlotScanLine viewer
    script might reveal that the midtones are OK, but that the darks are creeping down.
    This might indicate that the change in brightness is not occurring because of addition,
    but perhaps is a result of multiplication.


    Method 2: Using a Brightness Node
    If the Add node didn’t provide satisfactory results, a Brightness node might have a
    better effect. Attach a Brightness node, then enter the following expression into the
    value parameter:
    (PixelAnalyzer1.area1AverageRed@@1)/PixelAnalyzer1.area1AverageRed
    The expression uses the same basic approach as in Method 1, except that the color
    value from frame 1 is divided by the current frame’s color value. Since Brightness is a
    multiplier, this makes an adjustment based on the difference. As a result, if at frame 1
    the average red value is .5, and at frame 10 the average red value is .6, the above
    expression multiplies frame 10 by .83333 (.5/.6) to arrive at .5 again.


    Method 3: Using a Mult Node to Correct All Three Channels
    Method 2 assumes uniform variation across all three channels, which is probably
    wishful thinking. On the other hand, it’s fast and easy. A more accurate approach might
    be to feed similar expressions into the RGB channels of a Mult node.
    The following expressions are entered into the red, green, and blue parameters of a
    Mult node:
    (PixelAnalyzer1.area1AverageRed@@1)/PixelAnalyzer1.area1AverageRed
    (PixelAnalyzer1.area1AverageGreen@@1)/PixelAnalyzer1.area1AverageGreen
    (PixelAnalyzer1.area1AverageBlue@@1)/PixelAnalyzer1.area1AverageBlue
    This adjusts each channel according to the PixelAnalyzer node’s analysis of each
    channel of frame 1."
    Arkham
    RED#487


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