*Interpolated Halftoning, Rehalftoning, and Halftone Compression*

Prof. Brian L. Evans

Laboratory for Image and Video
Engineering

Dept. of Electrical and Computer Engineering

The University of Texas at Austin, Austin, Texas

Collaboration with Mr. Niranjan Damera-Venkata and Dr. Thomas Kite and

Wednesday, November 4, 1998, 3:00 PM

Hewlett-Packard Laboratories

Palo Alto, CA

With increasing number of dots per inch on printers, grayscale
images are often *interpolated and then halftoned*.
Using our LSI model, we can compensate for the frequency distortion
in interpolation and halftoning to produce halftones with the same
frequency response of the original plus noise, using only raster image
processing operations.
In a similar manner, we can *rehalftone* a scanned error
diffused halftone for a particular error diffusion printer in such
a way as to eliminate all frequency distortion.
Rehalftoning is essentially inverse halftoning followed by halftoning.
Because the inverse halftone will be halftoned, we show that we
can use a 4 x 4 FIR filter to perform the inverse halftoning.
This is in contrast to sophisticated inverse halftoning algorithms [1,2].

Interpolated halftoning and rehalftoning are useful in compressing halftones. Halftone compression is a key issue in the emerging JBIG2 standard, which is intended for the next-generation fax machines, printers, and scanners. The key problem with current fax machines is that they expand halftones. In JBIG2, halftones may be (1) compressed directly or (2) converted to a higher bitwidth and then each bit plane is compressed. Lossless compression is high for clustered dot halftones (5:1) but low for error diffused halftones (2:1). We propose to apply our work in rehalftoning for JBIG2 codecs and interpolated halftoning in JBIG2 decoders to improve the coding gain for error diffused halftones. We also propose to use our quality assessment techniques to rate JBIG2 codecs.

- N. Damera-Venkata, T. D. Kite, M. Venkataraman, and B. L. Evans,
"Fast Blind Inverse Halftoning",
*Proc. IEEE Int. Conf. on Image Processing*, Chicago, IL, Oct. 4-7, 1998, vol. 2, pp. 64-68. - T. D. Kite, N. Damera-Venkata, B. L. Evans, and A. C. Bovik,
"A High-Quality, Fast Inverse Halftoning Algorithm for Error
Diffused Halftoned Images",
*Proc. IEEE Int. Conf. on Image Processing*, Chicago, IL, Oct. 4-7, 1998, vol. 2, pp. 59-63. - T. D. Kite, B. L. Evans, T. L. Sculley, and A. C. Bovik,
"Digital Halftoning As 2-D Delta-Sigma Modulation",
*Proc. IEEE Int. Conf. on Image Processing*, vol. I, pp. 799-802, Oct. 26-29, 1997, Santa Barbara, CA.

Mail comments about this page to bevans@ece.utexas.edu.