---
title: "Disadvantage of intensity interpolation"
subject: "Computer Graphics"
chapter: 8
key: "semester_5/computer_graphics:intensity-interpolation-disadvantage"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/intensity-interpolation-disadvantage
site: BCT Engineering
---

# Disadvantage of intensity interpolation

Computer Graphics · Chapter 8: Illumination and Surface Rendering methods

- Asked in: 2071 Shrawan, 1 marks
- Video: [Gouraud Shading in computer graphics | Shading | Intensity Interpolation method | With example](https://www.youtube.com/watch?v=uKjzQkcz0wo) — Harmanpreet kaur
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/intensity-interpolation-disadvantage
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-8

## Question

Mention the disadvantage of the intensity interpolation technique.

## Short answer

Specular highlights inside a polygon may be missed or distorted because intensity is calculated only at vertices; the linear interpolation causes Mach bands at edges where intensity slope changes abruptly.

## Answer

The main disadvantage of the intensity-interpolation (Gouraud) technique is that **specular highlights inside a polygon may be missed or distorted**, because the illumination is calculated only at the vertices. It also produces **Mach bands** (bright or dark streaks) where the slope of the intensity changes at polygon edges.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the main disadvantage of intensity interpolation (Gouraud) shading?
   A. Specular highlights inside a polygon may be missed or distorted
   B. It needs a normal at every pixel
   C. It cannot shade triangles
   D. It gives the same intensity to the entire polygon
   Answer: A. Illumination is computed only at vertices, so a highlight in the polygon interior can be missed. (Key point: Highlight problem)

2. Why do Mach bands appear in Gouraud shading?
   A. Normals are interpolated at each pixel
   B. Intensity is interpolated linearly, so its slope changes abruptly at polygon edges
   C. Only one intensity is used per polygon
   D. The depth values are quantised
   Answer: B. Slope discontinuities at edges appear as bright or dark streaks. (Key point: Mach bands)

## Related in Computer Graphics

- [Gouraud shading for polygon rendering](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Agouraud-shading-intensity-interpolation) — Computer Graphics, chapter 8, asked 6×

## Related in other subjects

- [Newton interpolation: y(1.6), y(4.8)](https://www.bctengineer.com/question.md?key=semester_4%2Fnumerical_method%3Anewton-1-6-4-8) — Numerical Method, chapter 4