Adjusting Brightness

How to adjust RGB values to make an image brighter?

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Method 1: Simply scale pixel components  Must “clamp” to range, e.g. [0..1] or [0..255] Method 2: Blend pixels with black or white  Remains in valid range by construction.

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Adjusting Contrast

Intuitively, increase contrast:  Mid-level pixels remain unchanged.  Dark pixels get darker.  Light pixels get lighter.  Preserve average luminance. • Decrease contrast: push all pixels towards average luminance.

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Color to gray-levels

  1. What is Luminance?
  2. Measures perceived “gray-level” of pixel  L = 0.30red + 0.59green + 0.11*blue

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At every pixel: compute luminance L from RGB, then set RGB to (L,L,L)

Adjusting Gamma

Function originally accounting for nonlinearity in cameras and displays

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$$ I_{out}=I_{in}^\gamma $$

\gamma depends on camera and monitor.

Adjusting Saturation

Decrease / increase color saturation of every pixel Interpolate / extrapolate between original image and grayscale version of it