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LOCAL COSINE TRANSFORM A method for the reduction of the Blocking Effect in JPEG

Summary: LOCAL COSINE TRANSFORM ­ A method for
the reduction of the Blocking Effect in JPEG
appeared in Journal of Mathematical Imaging and Vision, Special Issue on Wavelets, Vol. 3, pp. 7­38, 1993
G. Aharoni y , A. Averbuch y , R. Coifman z , M. Israeli x
y School of Mathematical Sciences, Tel Aviv University,
Tel Aviv 69978, Israel
z Department of Mathematics, Yale University,
New Haven, CT 06520, USA
x Faculty of Computer Science, Technion, Haifa 32000, Israel
This paper presents the Local Cosine Transform (LCT) as a new method for the reduction
and smoothing of the blocking effect that appears in Discrete Cosine Transform (DCT) based
image coding algorithms at low bit rates. In particular the blocking effect appears in the JPEG
baseline sequential algorithm.
Two types of LCT were developed: LCT­IV which is based on the DCT type IV and LCT­II
based on DCT type II, which is known as the standard DCT. At the encoder side, the image
is first divided to small block of pixels. Both types of LCT have basis functions that overlap
adjacent blocks. Prior to the DCT coding algorithm, a preprocessing phase is applied on the
image in which the image is multiplied by a smooth cutoff functions (or bells) that overlap
adjacent blocks. This is implemented as folding the overlapping parts of the bells back into the


Source: Averbuch, Amir - School of Computer Science, Tel Aviv University


Collections: Computer Technologies and Information Sciences