[OpenCV Tutorial] $4 - Changing the contrast and brightness of an image!

Goal

In this tutorial you will learn how to:

• Access pixel values
• Initialize a matrix with zeros
• Learn what cv::saturate_cast does and why it is useful
• Get some cool info about pixel transformations

Theory

Image Processing

• A general image processing operator is a function that takes one or more input images and produces an output image.
• Image transforms can be seen as:
  • Point operators (pixel transforms)
  • Neighborhood (area-based) operators

Pixel Transforms

• In this kind of image processing transform, each output pixel's value depends on only the corresponding input pixel value (plus, potentially, some globally collected information or parameters).
• Examples of such operators include brightness and contrast adjustments as well as color correction and transformations.

Brightness and contrast adjustments

• Two commonly used point processes are multiplication and addition with a constant:
  g(x)=αf(x)+β
• The parameters α>0 and β are often called the gain and bias parameters; sometimes these parameters are said to control contrast and brightness respectively.
• You can think of f(x) as the source image pixels and g(x) as the output image pixels. Then, more conveniently we can write the expression as:
  g(i,j)=α⋅f(i,j)+β
  
  
  where i and j indicates that the pixel is located in the i-th row and j-th column.
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