20.8.4 Image Adjustment


Adjusting the contrast and brightness, hue and saturation, or other properties of the image is usually used to reveal or enhance the image details to get a "better", or "more useful" image for the processing or analysis that follows.

Brightness and Contrast

Origin provides many tools to adjust the brightness and contrast of an image, either by adjusting it pixel by pixel, or adjusting pixels as a group.

  • Adjustment: Brightness and Contrast
A general way of adjusting brightness and contrast of pixels individually, according to some direct mapping relationship (usually refer to as a "curve"). It is widely used in underexposed image adjustment.
Adjustment cvBC 01.png
  • Adjustment: Gamma
Adjusts the brightness and contrast by applying Gamma Correction and thus brings out the details that cannot display in the original image. It is original used but not limited in CRT display adjustment.
Human vision follows an approximate Gamma function under common illumination conditions. It means that human eyes are more sensitive to differences between darker tones than between lighter ones. If too many pixels of an image locate in light or dark area that cannot be differentiated by human eyes, the visual quality would be badly reduced. Gamma Correction takes advantage of the nonlinear characteristic of human vision to adjust the intensity distribution.
Adjustment cvGamma 02.png
See a comparison on the right. When Gamma value < 1 the image becomes darker, and Gamma value > 1 the image lighter. Larger the Gmma value, lighter the image, and thus bring the boats shape and grass at the low-right corner out of shadow.
Adjustment cvGamma 01.png
  • Histogram Adjustment
Adjusting contrast by Histogram is a typical way of adjusting pixels as a group. Histogram Adjustment (also called "histogram stretching") can normalize the histogram in one or all RGB channels to the range specified and thus "stretches" the contrast. Take the below images as an example. In the original image we can see most pixels' gray scales locate in a small range [115, 205], so the contrast is rather close. After normalization the distribution is stretched to whole range [0, 255], so the contrast is enhanced.
Original After Histogram Adjustment
Image Adjustment cvHistc 01.png Adjustment cvHistc 02.png
Histogram Adjustment cvHistc 03.png Adjustment cvHistc 04.png


  • Histogram Equalization
Equalizes the histogram of an image to enhances the contrast. It is extremely useful when the difference of intensity in the interested region is rather small. Take the below images as an example. We use the same image as the above section. After equalization the original gray scale values are mapping to whole range [0, 255], so the contrast is enhanced. By a close looking we can see that Histogram Equalization does a better job than Histogram Adjustment in handling details.
Original After Histogram Equalization
Image Adjustment cvHistc 01.png Adjustment cvHistEq 02.png
Histogram Adjustment cvHistc 03.png Adjustment cvHistEq 04.png

Hue and Saturation

Adjusts the hue and saturation of an image. To adjust Hue and Saturation, select

  • Adjustment: Hue and Saturation

Adjustment cvHS 01.png

Color Balance

Adjusts color of an image by altering the color level of R, G, B channel(s). It is widely used in color correction, and sometimes creatively used in artistic area. To perform Color Balance, select

  • Adjustment: Color Balance
Original Image After Color Balance
Adjustment cvColorBal 03.png Adjustment cvColorBal 04.png
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