B&W Conversion 1 – Desaturation

Yesterday provided an overview of three B&W conversion techniques. Each of them will be examined individually over the next three days. Today we’ll begin with desaturation.


NOT done by desaturation


A B&W conversion technique that you may want to avoid

Avoid? Why?

  • Because it has no redeeming features other than simplicity
    • Some editing software offer it as a menu option under COLOR thus tempting users to use it.
    • Don’t!
  • The resulting B&W conversions are rarely (like never) better than the alternatives
    • This is best illustrated by yesterday’s overview example

    Why would you ever use a B&W conversion that potentially could do this?

    Especially when there are better alternatives??


    How each desaturation is computed…

    Are you surprised that a straight desaturation of the color image, as a means of B&W conversion, produced a uniform gray image? Once you know how desaturation is accomplished the mystery will be solved.

    Desaturation B&W conversion is done by averaging the image’s RGB component values, pixel by pixel. The above image is pure RGB. This means that its color’s component R/G/B values from left to right are –

    • Red = 255/0/0
    • Green = 0/255/0
    • Blue = 0/0/255

    To determine each color’s gray conversion value, compute the average of each component’s strength –

    • Red = (255+0+0)/3 = 85
    • Green = (0+255+0)/3 = 85
    • Blue = (0+0+255)/3 = 85

    And, WOW, look at that! They’re all the same.They all convert to the same shade of gray. Maybe, just maybe – desaturation isn’t that great of a technique for B&W conversion (although at times you can get away with it; it depends on the image’s colors).

    Now we know why the desaturation option gave the result that it did in our R/G/B image test panel.

    Tomorrow – Grayscale

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