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At high compression levels, the quantization of DCT coefficients
used by the JPEG image format results in "blocking" artifacts. I have developed
a method for reducing those artifacts by creating a new smooth basis which can
recover non-blocky image from the same quantized DCT coeffients.
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Examples
(a)
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(b)
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Figure 1: An example of JPEG deblocking. Image (a) is a portion of the image Lena,
generated from a higly compressed JPEG stream. Compression is achieved by
high level of quantization to the DCT coefficients, resulting in
severe blocking artifacts when decompressed using the standard JPEG algorithm.
The image on the right shows the same JPEG source which has been decompressed
using my new method.
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(a)
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(b)
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Figure 2: A second example, again (a) shows the standard JPEG decompression, and (b) shows
decompression using my new method.
Notice that the blocking artifacts are greatly reduced; this is most
apparent in the smooth areas (such as the cheeks).
Additionally, 'ringing' artifacts -- such as those which are very visible around her lips --
are also suppressed with this method.
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(a)
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(b)
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Figure 3: A third example showing the improvment on an even more compressed (highly quantized) JPEG stream.
Even under such severe quantization, the recovered image is still quite good.
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How does it work?
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Figure 4: Each image depicts the (1,2) subband of the DCT decomposition of the Lena
subwindow shown in Figure 3.
Image (a) shows the full accuracy (non-quantized) inverse DCT;
when all full-accuracy subbands are added together the
original image is recovered exactly (upto floating point accuracy).
Image (b) shows the inverse DCT of the same subband after the coefficients have been quantized;
when all of the quantized subbands are added together the image in Figure 3a is recovered.
Image (c) shows the inversion of the quantized DCT coefficients using my new smooth basis.
Even though the coefficients have been quantized, the basis is smooth.
By adding to all such smooth subbands no blocking artifacts can occur, and the image in
Figure 3b is recovered.
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Page loaded on November 23, 2024 at 08:08 PM.
Page last modified on
2006-05-27
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Copyright © 1997-2024, Jeremy S. De Bonet.
All rights reserved.
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