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   -> Volume 5, Issue 4

Preprint: Visual thresholds for wavelet quantization error
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"Andrew B. Watson" (

PostPosted: Wed Dec 04, 2002 9:52 am    
Subject: Preprint: Visual thresholds for wavelet quantization error
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Preprint: Visual thresholds for wavelet quantization error

Authors: Andrew B. Watson,1, Gloria Y. Yang,2,
Joshua A. Solomon,3 & John Villasenor,4

ABSTRACT The Discrete Wavelet Transform (DWT) decomposes an image into
bands that vary in spatial frequency and orientation. It is widely
used for image compression. Measures of the visibility of DWT
quantization errors are required to achieve optimal
compression. Uniform quantization of a single band of coefficients
results in an artifact that is the sum of a lattice of random
amplitude basis functions of the corresponding DWT synthesis filter,
which we call DWT uniform quantization noise. We measured visual
detection thresholds for samples of DWT uniform quantization noise in
Y, Cb, and Cr color channels. The spatial frequency of a wavelet is r
2^-L , where r is display visual resolution in pixels/degree, and L is
the wavelet level. Amplitude thresholds increase rapidly with spatial
frequency. Thresholds also increase from Y to Cr to Cb, and with
orientation from low-pass to horizontal/vertical to diagonal. We
propose a mathematical model for DWT noise detection thresholds that
is a function of level, orientation, and display visual
resolution. This allows calculation of a "perceptually lossless"
quantization matrix for which all errors are in theory below the
visual threshold. The model may also be used as the basis for adaptive
quantization schemes.

1,3: NASA Ames Research Center, Moffett Field, CA, 94035-1000
2,4: Department of Electrical Engineering, UCLA, Los Angeles, CA

Citation: A.B. Watson, G.Y. Yang, J.A. Solomon and
J. Villasenor,"Visual thresholds for wavelet quantization error,"
Human Vision and Electronic Imaging, B. Rogowitz and J. Allebach,
2657, 382-392, The Society for Imaging Science and Technology, (1996).

PDF file is available at

Andrew B. Watson MS 262-2 NASA Ames Research Center Moffett Field CA
94035-1000 (415) 604-5419 -3323 fax
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