B&W Conversion 2 – Grayscale

Today we’ll look at the 2nd of three B&W conversion techniques, grayscale.Tomorrow it will be luminosity.

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Portland Head Light

Dark (well before sunrise) misty scene (the kind I love)


How is Grayscale computed?

  • Grayscale attempts to take into account how our vision perceives color.

We do not perceive all colors as being equally bright

  • Green is seen as being brighter than red which is brighter than blue.

In order to convert colors to match the colors the way that we see them (more or less)

  • We can’t simply average all three colors equally as in the desaturation method
  • We must weight each color proportionally to how our eyes see them
  • The accepted weightings are:
    • 30% of the red value
    • 59% of the green value, and
    • 11% of the blue value
    • Not equal weights as in desaturation

The weighted average gives us the grayscale shown in example below.

  • Often, it is hard to see a difference between luminance and grayscale
  • This RGB test panel example shows that there is one – especially the green

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Tomorrow – Luminosity


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