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  1. Member
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    Aug 2013
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    I've been adjusting the levels in AviSynth to get darker blacks and whiter whites. My original source is a VHS tape captured in Virtual Dub with ATI AIW with proc amp adjustments and i tried to keep out of the red areas to prevent clipping the blacks/whites. So i imagine this is keeping within the 235 range?

    Onto Avisynth and after i've applied SmoothTweak(brightness=-14, contrast=1.16, saturation=1.14) which is identical to ColorYUV(levels="TV->PC") though with better control over the adjustments, i'm pretty happy with the results. Blacks look black and whites look white. But i'm just concerned i've crushed blacks and lost detail? Is anything supposed to go in the brown area of the histogram?

    After levels adjustment
    Image
    [Attachment 67745 - Click to enlarge]


    Before levels adjustment
    Image
    [Attachment 67750 - Click to enlarge]


    I notice the line hasn't gone flat, and there is jagged edges, does this mean no detail has been crushed?
    Image
    [Attachment 67749 - Click to enlarge]


    An example of something on-screen surrounded by darkness
    Image
    [Attachment 67747 - Click to enlarge]


    Before levels adjustment
    Image
    [Attachment 67751 - Click to enlarge]
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  2. Too much brightness reduction.
    Code:
    SmoothTweak(brightness=-6, contrast=1.1, saturation=1.0)
    keeps levels within the legal range.
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  3. Member
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    Thanks. Though i do want the blacks to be black, rather than slightly washed out.

    For example, this is a video playing in the media player.. is there anyway to get these black bars as dark as the pillarbox in the player? So getting it to black without removing the noise (detail) moreso for other darks in the video?

    Image
    [Attachment 67766 - Click to enlarge]


    Image
    [Attachment 67763 - Click to enlarge]
    Image Attached Files
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  4. In real analog video pure black does not exist because of the fluctuations caused by the noise. So if you don't want to loose any details by clipping you will have to find a compromise how to set the "black" level of the dark scenes or dark parts of the picture, and/or you can try to denoise as far as reasonable.
    For the second example you know that the bars should be pure black without any details. Hence you can simply substitute the captured bars by synthesized bars, like
    Code:
    AVISource("Original File.avi")
    crop(6,68,-6,-68)
    addborders(6,68,6,68)
    For the first example you could try to build a mask which leaves the yellow squares on the top an bottom alone and set the rest of the borders to black.
    Last edited by Sharc; 23rd Nov 2022 at 03:20.
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