Intensity Transformation

Intensity transformation as the name suggests, we transform the pixel intensity value using some transformation function or mathematical expression.

Intensity transformation operation is usually represented in the form

s = T(r)

where, r and s denotes the pixel value before and after processing and T is the transformation that maps pixel value r into s.

Basic types of transformation functions used for image enhancement are

  • Linear (Negative and Identity Transformation)
  • Logarithmic (log and inverse-log transformation)
  • Power law transformation

The below figure summarize these functions. Here, L denotes the intensity value (for 8-bit, L = [0,255])

source: R. C. GonzalezR. E. Woods, Digital Image Processing

This is a spatial domain technique which means that all the operations are done directly on the pixels. Also known as a point processing technique (output depend only on the single pixel) as opposed to neighborhood processing techniques(like filtering) which we will discuss later.


  • To increase the contrast between certain intensity values or image regions.
  • For image thresholding or segmentation.
Before Thresholding
After Thresholding

In the next blog, we will discuss these different transformation functions in detail. Hope you enjoy reading.

If you have any doubt/suggestion please feel free to ask and I will do my best to help or improve myself. Good-bye until next time.

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