A Study of Possible Improvements in JPEG Compression with Applications in High Compression and Wirel

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A Study of Possible Improvements in JPEG
Compression with Applications in High Compression
and Wireless Transmission

• Andrew Puryear
• PSYCH221/EE362
• March 13, 2003

http//ise.stanford.edu/apuryear/
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Outline

• PART I COLA-JPEG
• The COLA-JPEG is aimed at mitigating the
  blockiness inherent in the JPEG compression
  scheme at high compression ratios using a
  Constant OverLap Add window instead of a
  rectangular window.
• PART II JPEGa
• The JPEGa is aimed at coding an image so that it
  will be amenable to transmission over hostile
  wireless channels.

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Highly Compressed JPEG

• Blockiness visible in the image is a general
  phenomenon apparent in JPEG images with high
  compression ratios.

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JPEG Compression Process
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JPEG Compression Process
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JPEG Compression Process
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JPEG Compression Process
Quantizer Weights the various spectral
coefficients according to their importance, with
respect to the human visual system.
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COLA-Window

• The COLA window is 10-by-10 pixels, maximum of
  one, first step down 0.75, and second step down
  of 0.25.
• The window has the property that, with a hop size
  of 8 (in linear combination of horizontal and
  vertical), it overlaps and adds to a constant
  value of one.

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COLA-Window (Cont.)

• COLA Window Pros
• Because it is Constant OverLap Add, perfect image
  reconstruction is possible (with out compression)
• Each image block contains part of its
  surrounding blocks hopefully this will suppress
  the blockiness
• COLA Window Cons
• COLA Window is 36 larger than the rectangular
  window and therefore requires increased
  quantization for fair comparisons.

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COLA-JPEG Comp./Expan.
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COLA-JPEG Results Zero Compression
JPEG
COLA-JPEG
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COLA-JPEG Results Compression Ratio 3
JPEG
COLA-JPEG
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COLA-JPEG Results Compression Ratio 9
JPEG
COLA-JPEG
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COLA-JPEG Results Compression Ratio 9
COLA-JPEG
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Outline

• PART I COLA-JPEG
• The COLA-JPEG is aimed at mitigating the
  blockiness inherent in the JPEG compression
  scheme at high compression ratios using a
  Constant OverLap Add window instead of a
  rectangular window.
• PART II JPEGa
• The JPEGa is aimed at coding an image so that it
  will be amenable to transmission over hostile
  wireless channels.

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JPEGa The Wireless Ready JPEG
Todays vision information is increasing being
transferred via wireless technologies such as a
laptop with a wireless card or a mobile phone
with photo-display technology.
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JPEGa

• The JPEGa standard improves the binary encoding
  step in the JPEG standard to make the image more
  robust to possible errors during transmission. In
  this standard, everything is the same as the JPEG
  except for the Binary Encoder/Decoder.

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JPEGa Convolutional Encoder

• The improvement is made by convolutionally
  encoding the binary sequence. The scheme allows
  for low bit error rates (BER) even with low
  signal to noise ratios.

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JPEGa Binary Decoder

• The received image is decoded using the so-called
  Viterbi algorithm. The algorithm looks at the
  received string (15 bits long in this case) and
  minimizes the hamming distance between it and all
  allowed strings of length 15.
• More info can be found at
• http//ee.tamu.edu/ee489/original/MOD_COD.PDF
• Page 70.

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JPEGa Performance

• To determine the performance of the JPEGa
  standard, I simulated its transmission trough a
  wireless channel including the effects of pulse
  shaping, additive white Gaussian noise, and
  matched filter detection.
• Results are compared with JPEG images transmitted
  through the same channel.

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JPEGa Simulation Details
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JPEG Simulation Details
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Results
4dB
6dB
8dB
10dB
JPEGa
JPEG
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Conclusions References

• Two possible improvements to the JPEG image
  compression standard have been presented. The
  first proposed improvement, the COLA-JPEG, was
  aimed at mitigating the blockiness inherent in
  the JPEG compression scheme at high compression
  ratios using a Constant OverLap Add window
  instead of a rectangular window. This proposed
  improvement, while being instructive, proved to
  offer no advantage over JPEG. The second proposed
  improvement, the JPEGa, was aimed at coding the
  image so that it would be amenable to
  transmission over hostile wireless channels. This
  proposed improvement provides a 4dB gain over the
  JPEG standard for quality reception at the
  expense of increased complexity.

References 1 Introduction to JPEG -
http//www.faqs.org/faqs/compression-faq/part2/sec
tion-6.html 2 Welcome to the JPEG Tutorial! -
http//www.ece.purdue.edu/ace/jpeg-tut/jpegtut1.h
tml 3 B. Wandell, Compression and
Multiresolution - http//coursework.stanford.edu/c
oursework/servlet/ShowFile?contentid36070 4
T.S. Rappaport, Wireless Communications -
Principles and Practice, 2nd Edition, Prentice
Hall, 2001. 5 S. Haykin, Communication Systems.
New Wiley, 2002. 6 G. L. Stüber, Principles of
Mobile Communication, 2nd Edition, Kluwer
Academic Publishers, 1996.