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RGB values, and the other one?

MrWriter
In Capture One Pro 20 when I hover the mouse curser over the image and more it around there are RGB values across the top that change also, but there is a fourth value in grey, what is this value?
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4 comments

Date Votes
  • Ian Wilson
    Moderator
    Top Commenter
    The other one is the total luminance at that point. If you were to desaturate the image, that would be the value. Compare this with the with Histogram tool, where you will see four curves, a grey one and R, G, and B.

    Ian
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  • MrWriter
    Thanks, Ian, new to histograms and C1 so have to try and figure out how to read histogram and what they mean. Looking for a decent tutorial on it, in laymen's terms.
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  • Ian Wilson
    Moderator
    Top Commenter
    In simple terms the histogram is a graph of how many pixels there are at each brightness level in your image, from 0 (pure black) to 255 (maximum brightness). (If you could hover the mouse over each pixel in turn and log the values you see at the top of the screen, you would get the data for that graph.)

    If there is a small range of brightness in the scene you photograph, the histogram may not reach as far as 0 on the left or 255 on the right. But if there is a wide range (perhaps bright sun in some places, but deep shadows in others) the range of tones may exceed the possible dynamic range of the camera sensor, and the histogram may be bunched up against the 0 end or the 255 end or both. That will mean loss of detail in the shadows, or in the highlights or in both.

    One of the instructive things to notice is that the grey histogram may be within bounds at either end but one of the colours may still be bunched up at the side. So the red channel might be overexposed even if the grey histogram looks OK.

    I found this explanation online which you may find instructive.

    https://www.azuloxworkshops.com/educational/capture-one/capture-one-histograms-levels/

    Also this video (based on an older version of Capture One , but the principle is the same for this feature.)

    https://photography.tutsplus.com/tutorials/how-to-use-the-histogram-in-capture-one--cms-28591

    Ian
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  • MrWriter
    Thanks. Just watched the video, already knew those basics. Will read the longer article now. Thanks again, Ian.
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