CpE 491: Information Systems Engineering II
(Homework 2)
Assigned on: February
12, 2001
Due back on: February
26, 2001
- Use
the uniform quantizer program provided in the same ftp site to uniformly
quantize the Sena image. Do this for various numbers of quantizer bins
(N). For each quantized image calculate the distortion due to quantization
(D) and plot it against the rate of the quantizer (R ).
- Do the
exact same thing as above, but also add a Huffman code module at the end.
So, now the rate of at which the image is compressed is given by the
number of bits you actually spend in encoding the image (after Huffman
coding). Is there any difference between the plot that you see in this
question and the one you generated in the previous question? Comment on it.
- The
source code for JPEG is available (for free) at ftp.uu.net:/graphics/jpeg/jpegsrc.v6b.tar.gz.
You can also find the ZIP archive format at ftp.simtel.net:/pub/simtelnet/msdos/graphics/jpegsr6b.zip
(for PCs). If you are using “attila” it is already installed there. You
can also find these codecs at http://www.ece.stevens-tech.edu/~cpe491/Codecs
directory. The command to compress an image is “cjpeg” and the decoder
command is “djpeg”. To learn more about how to use these commands you can
type “man cjpeg” at the UNIX prompt. Having said all this, here is the
question:
- Compress
the Sena image at various bit rates, starting from 0.75 bits per pixel to
about 0.2 bpp. Plot the SNR versus R curve. From the reconstructed images
(view them using xview in Solaris or Irfan view or other viewer on PCs)
at these rates, what conclusions can you draw regarding the quality of
the compressed images? What strikes you most about the distortions you
see at the lower rates? Can you comment on what can be done to remove
those? Include the PSNR Vs R plot and some images as well in your answer
sheet.