Find index of unique pixel values and assign a different pixel value to the grayscale image.

I have a grayscale image in which objects are represented as:

Object Pixel Value

Background 0

Class 1 1

Class 2 2

Class 3 3

Class 4 4

Class 5 5

There are no other pixel values except the 6 mentioned above. Background is essentially present, other objects may or may not be present.

The requirement is to assign different pixel value to the objects

Object Pixel Value New Pixel Value

Background 0 0

Class 1 1 50

Class 2 2 100

Class 3 3 150

Class 4 4 200

Class 5 5 250

For an example, i am attaching an image with Background, Class 4 and Class 5

What is the most optimized method to find and replace pixel values in a grayscale image?

[Walter Roberson]

This appears to duplicate https://www.mathworks.com/matlabcentral/answers/1770150-find-index-of-unique-pixel-values-and-assign-a-color-to-the-image-original-image-is-a-grayscale?s_tid=srchtitle

[Rishi Raj]

Although similar.. i wanted to know the best way to change pixel values and keep a grayscale to grayscale image

Answer 1

[Walter Roberson]

map = cast(0:50:250, class(Img));

NewImg = map(Img + 1);

Or more simply,

NewImg = Img .* 50;