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5. gray level transformation
- 1. Gray level transformation By Md. Fazle Rabbi 16CSE057
- 2. 4.2 Introduction • All Image Processing Techniques focused on gray level transformation as it operates directly on pixels. • The gray level image involves 256 levels of gray and in a histogram. • Horizontal axis spans from 0 to 255. • The vertical axis depends on the number of pixels in the image.
- 3. 4.3 Introduction The simplest formula for image enhancement technique is: s = T * r Where T is transformation, r is the value of pixels, s is pixel value before and after processing. r = f(x,y) s = g(x,y) 'r' and 's' are used to denote gray levels of f and g at(x,y)
- 4. 4.4 Types of Transformation There are three types of transformation: 1.Linear 2.Logarithmic 3.Power - law
- 5. 4.5 Linear Transformation The linear transformation includes 1. identity transformation and 2. negative transformation.
- 6. 4.6 In identity transformation, each value of the image is directly mapped to each other values of the output image. Linear Transformation
- 7. 4.7 Linear Transformation Negative transformation is the opposite of identity transformation. Here, each value of the input image is subtracted from L-1 and then it is mapped onto the output image s = (L – 1) – r
- 8. 4.8 Logarithmic transformations Logarithmic transformation is divided into two types: 1. Log transformation 2. Inverse log transformation The formula for Logarithmic transformation s = c log(r + 1) Here, s and r are the pixel values for input and output image. And c is constant In the formula, we can see that 1 is added to each pixel value this is because if pixel intensity is zero in the image then log(0) is infinity so, to have minimum value one is added.
- 9. 4.9 Logarithmic transformations Log The inverse log transform is opposite to log transform
- 10. 4.10 Power - Law transformations Power Law Transformation is of two types of transformation nth power transformation and nth root transformation. Formula: Here, γ is gamma, by which this transformation is known as gamma transformation. cr s γ < 1: changes darker to brighter images γ > 1: changes brighter to darker images
- 11. 4.11 Power - Law transformations Gamma = 10 Gamma = 8 Gamma = 6 γ > 1: changes brighter to darker images
- 12. 4.12 Power - Law transformations γ= .6 γ= .3 γ= .4 γ < 1: changes darker to brighter images
- 13. 4.13 Thank You