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Color match area

Nov 18, 2012 9:41 PM

Tags: #grayscale

I have a B&W pic I'd like to sum the overall grayscale values into one number and create a swatch from this. How would one do this?

 
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  • Currently Being Moderated
    Nov 19, 2012 1:37 AM   in reply to luca del carlo

    With Photoshop, perhaps. Blur-and-blur-some-more until your image is all but a gray blur. Then measure it.

     
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  • Rob Day
    3,134 posts
    Oct 16, 2007
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    Nov 19, 2012 5:15 AM   in reply to luca del carlo

    PhotoShop's Histogram panel in expanded view gives the median pixel value. So in this case it would be 100|100|100 RGB:

     

    Screen shot 2012-11-19 at 8.06.28 AM.png

     
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  • Currently Being Moderated
    Nov 19, 2012 5:15 AM   in reply to Rob Day

    It shows a value "100", so I'm guessing this is not a percentage . So this must be in 1/256ths? Or, if the maximum value for all-white is "255", 1/255ths?

     

    Wait -- that cannot be right, I just called up a simple graphic (black lines on white background) and it shows "255". Maybe you should look at the "Mean" value, 2 items up? Statistics is one of the few fields of maths in which I'm surprisingly bad, I could not recall the difference between Mean, StdDev, and Median if my life depended on it ...

     
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  • Rob Day
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    Oct 16, 2007
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    Nov 19, 2012 5:38 AM   in reply to [Jongware]

    You're right Mean is the average.

     
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  • Currently Being Moderated
    Nov 19, 2012 5:59 AM   in reply to Rob Day

    <g> I tried my blur/blur/blur/and blur even more, but it doesn't lead to anything useful after all.

     

    Since the Mean is "109.88" in your image, I suspect this isn't a percentage either If it is 1/256ths, there still is a lingering question ... Luca wants a grayscale swatch, which is measured as a percentage of [Black], that is, 0% is white and 100% is full black.

     

    So would the value needed be 109.88/256 * 100% = 42.9% [Black] or does Photoshop measure "the other way around", as usual for RGB, and is the value of Black therefore 100 - 42.9 = 57.1%?

     
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  • Rob Day
    3,134 posts
    Oct 16, 2007
    Currently Being Moderated
    Nov 19, 2012 6:30 AM   in reply to [Jongware]

    Black therefore 100 - 42.9 = 57.1%?

     

    I think that's probably right. Photoshop's Curve dialog lets you choose between 8-bits and ink percentage:

     

    Screen shot 2012-11-19 at 9.26.57 AM.png

     

    Screen shot 2012-11-19 at 9.27.05 AM.png

     
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