Assignment 2
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Transcript of Assignment 2
Image and Video Compression
Homework # 2
Due date: 18 October 2015 : 11: 59 : 59 P.M.
Summary: This assignment addresses predictive coding, the DCT, and its use for imagecompression using VcDemo software. The software and reference images are uploaded on Slate.The related VcDemo tools are found in the “Basic Compression” and “Linear Transforms” menus.
Instructions: The homework can be done individually or in a group of two people at most. A report containingsummary of the results, with a brief discussion on the questions provided for each exercise has to besubmitted by each group. The provided comments should be concise and the report should not bemore than 4 pages long.
Images to be used: each group shall perform every exercise using two images: a natural image and asynthetic image (either Odie256B or zone256B).
VcDemo can open images in bmp or tiff format (beware: tiff format must be uncompressed). It issuggested to use the bmp format.
Exercise 1: PCM
Apply PCM compression (i.e., quantization of the pixel values), with no dithering and no errors,with bitrates of 1, 3, and 4 bpp. Analyze the visual quality and the PSNR. Quantization theoryindicates that, for each additional bit, the PSNR improvement should be roughly 6 bpp. Is thisalways true?
Then apply errors choosing a certain biterror rate (BER). What is the effect of the errors?
Optional:Evaluate the effect of using different prediction models for DPCM on the compressionperformance.
Exercise 2: DCT
The DCT module computes the DCT of an image and performs coding in the style of JPEG, withDC prediction, quantization and possibly entropy coding.Select two bitrates, one <= 1 bpp and the other > 1 bpp. For each bitrate:
Evaluate the performance gain obtained by performing entropy coding as opposed to noentropy coding.
With entropy coding enabled, evaluate the performance difference between the low (<= 1bpp) and high (> 1 bpp) rate.
With entropy coding enabled, evaluate the performance difference between predicting onlythe first (DC) coefficient of the DCT, and all the coefficients. Justify the results.
At bitrate of 1 bpp and with entropy coding enabled and prediction of only the DC
coefficient, evaluate the effect of the DCT block size. Briefly comment the difference of the results for the natural and synthetic images.