A two-dimensional generalization of the Haar transform which is used for the compression of astronomical images. The algorithm consists
of dividing the
image into blocks of
pixels, calling the pixels in the block , , , and . For each block, compute the four coefficients
(1)
(2)
(3)
(4)
Construct a
image from the
values, and repeat until only one value remains. The H-transform can be performed in place
and requires about
additions for an
image.
Capaccioli, M.; Held, E. V.; Lorenz, H.; Richter, G. M.; and Ziener, R. "Application of an Adaptive Filtering Technique to Surface Photometry
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69-80, 1988.Fritze, K.; Lange, M.; Möstle, G.; Oleak, H.; and Richter,
G. M. "A Scanning Microphotometer with an On-Line Data Reduction for Large
Field Schmidt Plates." Astron. Nachr.298, 189-196, 1977.Richter,
G. M. "The Evaluation of Astronomical Photographs with the Automatic Area
Photometer." Astron. Nachr.299, 283-303, 1978.White,
R. L.; Postman, M.; and Lattanzi, M. G. "Compression of the Guide
Star Digitised Schmidt Plates." In Digitised
Optical Sky Surveys: Proceedings of the Conference on "Digitised Optical Sky
Surveys" held in Edinburgh, Scotland, 18-21 June 1991 (Ed. H. T. MacGillivray
and E. B. Thompson). Dordrecht, Netherlands: Kluwer, pp. 167-175,
1992.
image into blocks of 
pixels, calling the pixels in the block 
, 
, 
, and 
. For each block, compute the four coefficients
image from the 
values, and repeat until only one 
value remains. The H-transform can be performed in place
and requires about 
additions for an 
image.
