Question

What is a histogram? Explain linear contrast stretching to improve the quality of an image.

Hint:

Think of it like a crumpled rubber band. The data is bunched up in the middle. Contrast stretching pulls both ends of the rubber band out so you can see all the details clearly!

Answer 1

Step 1: Concept
Digital image enhancement involves manipulating the pixel values of a satellite image to make specific features more visible to the human eye.

Step 2: Meaning
A histogram visualizes the distribution of pixel brightness, while contrast stretching is a mathematical technique applied to that distribution to improve image clarity.

Step 3: Analysis

• Histogram: It is a graphical representation showing the frequency of occurrence of each digital number (brightness value) in an image. The X-axis represents the pixel values (e.g., 0 to 255), and the Y-axis represents the number of pixels with that value.
• Linear Contrast Stretching: Unprocessed images often have low contrast, meaning their pixel values are clustered in a narrow range on the histogram (making the image look gray or washed out).
• Linear contrast stretching mathematically uniformly expands this narrow range of original values to fill the maximum possible dynamic range of the display (e.g., pulling the lowest value to 0 and the highest to 255).

Step 4: Conclusion
By stretching the histogram, the distinction between dark and light pixels increases, significantly improving the visual quality and contrast of the image. Final Answer: A histogram is a graph showing the frequency distribution of pixel brightness values in an image. Linear contrast stretching improves image quality by uniformly expanding a narrow range of original pixel values to utilize the full available display range (like 0-255), thereby increasing the image's overall contrast.