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Journal of Electronic Imaging

Finding maximum JPEG image block code size
Author(s): Gopal Lakhani
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Paper Abstract

We present a study of JPEG baseline coding. It aims to determine the minimum storage needed to buffer the JPEG Huffman code bits of 8-bit image blocks. Since DC is coded separately, and the encoder represents each AC coefficient by a pair of run-length/AC coefficient level, the net problem is to perform an efficient search for the optimal run-level pair sequence. We formulate it as a two-dimensional, nonlinear, integer programming problem and solve it using a branch-and-bound based search method. We derive two types of constraints to prune the search space. The first one is given as an upper-bound for the sum of squares of AC coefficients of a block, and it is used to discard sequences that cannot represent valid DCT blocks. The second type constraints are based on some interesting properties of the Huffman code table, and these are used to prune sequences that cannot be part of optimal solutions. Our main result is that if the default JPEG compression setting is used, space of minimum of 346 bits and maximum of 433 bits is sufficient to buffer the AC code bits of 8-bit image blocks. Our implementation also pruned the search space extremely well; the first constraint reduced the initial search space of 4263 nodes down to less than 232 nodes, and the second set of constraints reduced it further by 97.8%.

Paper Details

Date Published: 11 July 2012
PDF: 8 pages
J. Electron. Imag. 21(3) 033003 doi: 10.1117/1.JEI.21.3.033003
Published in: Journal of Electronic Imaging Volume 21, Issue 3
Show Author Affiliations
Gopal Lakhani, Texas Tech Univ. (United States)

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