Mahmoud R. El-Sakka, Khaled Hassanein, and Mohamed S. Kamel,
"An Optimized JPEG Quantizer for Financial Document Images",
SPIE International Conference on Applications of Digital
Image Processing XXI, Vol. 3460, pp. 530-538, July 1998, San
Diego, California, USA.
In this paper, two schemes for optimizing the JPEG quantizer
are investigated. The first scheme starts from a given
quantization-table and executes a sub-optimal search for
quantization-table parameters. Those parameters, when changed
by a pre-specified incremental step-size, result in the most
optimal move towards decreasing (increasing) the compressed
file-size, with a minimal increase (maximum decrease) of
error. This procedure is repeated, until a pre-specified
file-size is reached. The second scheme is based on performing
a mapping from the JPEG default quantization-table to an
optimized one. This mapping adapts the default
quantization-table to the statistics of the DCT coefficients
of the image at hand.
The superiority of these two optimized JPEG quantizers is
established in terms of the visual quality of their
reconstructed images. This was done by running comparative
visual image quality experiments involving 20 human subjects.
These optimized quantizers were also demonstrated to result
in a higher level of machine image quality, by improving the
accuracy of cheque amount reading applications. Experimental
results indicate that the second optimization scheme yields a
higher level of visual image quality, while requiring a
fraction of the processing time used by the first scheme.