Digital Image Processing With Photoshop Lab Exercise 1
1.- Huffman coding & RLE (This practice exercise is similar to an in-lab quiz you’ll do in the first lab) Consider an 8x8 image with eight possible gray levels, 0,1,2,3,4,5,6,7 as shown below: 00000000 00001111 22222222 33333333 33333333 33333333 44445555 66667777 (a) Calculate probabilities of the eight gray levels. (b) Calculate the entropy. (c) Calculate the average length of fixed-length code and code efficiency. Code H , where H is the entropy of a source and L is the average code length efficiency = L for the coding scheme. (d) Apply reduction process to construct a compact variable-length Huffman code, illustrate the codeword construction process, and calculate code efficiency with respect to entropy. (e) What is the minimum size of the compressed image taking into account the code table. Justify that your design is of the code table, and why it is efficient. (f) Suppose we have the next bit stream representing an image. Use RLE to encode the bit stream and then use Huffman to encode the run lengths. What’s the resulting size in bytes?
00001010101111100010111111110010110011011111111111111111111100001110 00001111111110010101001010010101111111000000000000000011010000111011
2.- JPEG performance measurement
a) To do in the lab session: convert the BMP image provided in the lab to JPEG and save it with different qualities. For each quality, change the image resolution and fill the next table using the resulting image size.
10 Image Quality/Resolution(%) (%) 1 2 3 4 5 6 7 8 9 10
20 (%)
30 (%)
40 (%)
50 (%)
60 (%)
70 (%)
80 (%)
90 (%)
100 (%)
b) To hand-in before the next lab session: with the information gathered in a), plot your data comparing the performance curves and provide an analysis of your results (explain with your own words).