Explain Pseudocolor Image Processing. Describe intensity slicing and color coding with a neat diagram.

Pseudocolor Image Processing

Pseudocolor image processing (also called false color processing) is the technique of assigning colors to different gray levels in a grayscale image. This is done to enhance the visibility of image features for human interpretation.

• In grayscale images, humans can distinguish only around 20 shades of gray.
• In contrast, we can differentiate thousands of colors.
• So, converting grayscale data into color helps in better visualization of patterns, edges, and details.

Pseudocolor is used mainly for:

• Medical imaging
• Satellite images (like rainfall or temperature maps)
• Scientific data interpretation
• Multispectral image analysis

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1. Intensity Slicing

Intensity slicing is one of the simplest forms of pseudocolor processing.

• It involves dividing the intensity (gray level) range of an image into several slices or intervals.
• Each slice is assigned a specific color.

Basic Idea:

Imagine the grayscale image as a 3D surface (intensity vs x-y plane).

• Then, place horizontal slicing planes at specific intensity levels.
• Each slice between two planes is colored differently.

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xample Formula:

Let the image intensity range be divided using P planes at levels:
l₁, l₂, ..., lP

Then we get P+1 intervals:
I₁, I₂, ..., IP+1

Each pixel (x, y) is assigned a color ck depending on its intensity level:

If f(x, y) ∈ Ik, then f(x, y) = ck
Where: ck = color for interval Ik

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2. Color Coding

In color coding, a mapping is defined between ranges of gray levels and specific RGB color values.

• For example:
  • 0–50 → Blue
  • 51–150 → Green
  • 151–255 → Red

This method helps to easily differentiate regions of different brightness.

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3. Intensity-to-Color Transformation (Advanced Pseudocolor)

A more flexible method involves:

• Applying three separate transformations on grayscale intensity
• The results are sent to Red, Green, and Blue channels of a color monitor

This method can use:

• Piecewise-linear functions (like intensity slicing)
• Or nonlinear functions for smoother gradients

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4. Multispectral Pseudocolor

Sometimes, instead of one grayscale image, three different grayscale images are used (from different sensors/bands).
Each is assigned to one of the RGB channels:

• Image 1 → Red
• Image 2 → Green
• Image 3 → Blue

Used widely in remote sensing and satellite image analysis.