Title: A Comparison of Still-Image Compression Standards and Proposed Methods for Improving Lossy Image Quality
1A Comparison of Still-Image Compression Standards
and Proposed Methods for Improving Lossy Image
Quality
- MDDSP Literature Survey Presentation
- Eric Heinen
2Project Goals
- Investigate existing methods for improving JPEG
image quality - Consider adapting these methods to JPEG2000
- Novel approaches?
- Compare image quality of JPEG and JPEG2000 (with
without improvements) across - Image set
- Compression ratios
3Joint Thresholding and Quantizer Selection for
JPEG Encoding(M. Crouse and K. Ramchandran, 1997)
- Optimize encoding without affecting decoding
- Rate-Distortion optimization framework
4Improved JPEG Compression Using Human Visual
System (HVS) Model(G. Sreelekha and P. S.
Sathidevi, 2005)
- Exploits contrast sensitivity of HVS
- Sinusoid at given frequency requires certain
amount of contrast to elicit a response - HVS is insensitive to very low and very high
frequencies - Contrast Sensitivity Function (CSF)
- CSF Thresholding
- Discard DCT coefficients below CSF value
5Improved JPEG Compression Using Human Visual
System (HVS) Model(G. Sreelekha and P. S.
Sathidevi, 2005)
- Also exploits masking property of HVS
- Vision less sensitive to local variation in
brighter regions - Compute luminance masking threshold based on
blocks DC coefficient - DCT coefficients below this threshold discarded
- Quantization after thresholding
- different from JPEG standard
- incompatible with JPEG standard decoder
6JPEG2000 vs. JPG
- Arbitrary rectangular tile size allowed
- Color space transformation can be
- Lossless (YUV)
- or lossy (YCbCr)
- Discrete Wavelet Transform (DWT)
- More sophisticated entropy encoding
- Improvements to JPEG can be applied
7Image Quality Assessment
- Full-reference image quality metrics (IQM)
- Estimate DMOS
- Convenient
- Popular IQMs
- Peak Signal to Noise Ratio (PSNR)
- Universal Image Quality Index
- Structural Similarity (SSIM)
8Statistical Evaluation of Recent IQMs(H. R.
Sheikh, M. F. Sabir, and A. C. Bovik, 2006)
- Image database
- Set of distortions
- JPEG, JPEG2000, White Noise, Gaussian Blur,
simulated wireless channel - Collect mean opinion scores
- 3 different performance metrics
- RMSE between IQM score and DMOS after non-linear
regression
IQM RMSE
PSNR 13.4265
JND 10.2649
DCTune 16.2150
PQS 10.4221
NQM 11.4698
Fuzzy S7 15.3544
BSDM (S4) 9.7934
SSIM (MS) 9.3691
IFC 9.0007
VIF 8.2459
9Questions?