Mathematics of Image Processing
Worksheet #4 - Quantization -Dequantization
Name: Box #:
Consider the 4x4 matrix which has been plucked from the clown image
Y=
2222
61 69 69 69
69 61 69 61
61 69 61 61
The 2D DCT of Yis:
Z=
197.0000 0 −4.0000 0
−78.6179 −3.6569 1.5307 0.8284
−67.0000 2.1648 0 −5.2263
−35.6261 4.8284 3.6955 7.6569
1. Now write down two different quantization matrices:
Q1=
Q1=
In the first one pick a uniform step for all frequencies. In the second one let the step size
vary with the frequencies.
2. Compute the results of scalar quantization
Z1=
Z2=
1
