Image analysis – Image transformation or preprocessing – Changing the image coordinates
Patent
1994-06-23
1999-12-14
Au, Amelia
Image analysis
Image transformation or preprocessing
Changing the image coordinates
382250, 382166, G06T 340
Patent
active
060028092
ABSTRACT:
The objects of this invention are accomplished by combinging the inverse DCT of an appropriate size with scaling on the resulting reconstructed image. In particular, if the data is stored as DCT values of blocks of size P.times.Q and an output image is to be scaled by a factor of R in one dimension and S in the second dimension, then the process is performed in two stages. First a scaling of factor K1/P in the first dimension and a scaling of factor L1/Q in the second dimension are done by inverse transforming with 2-dimensional DCTs of size K1.times.L1. A factor .sqroot.(K1/P).times..sqroot.(L1/Q) is absorbed into a dequantization process prior to the inverse transorm process. Then a scaling of factor K2/K3 in the first dimension and a scaling of factor L2/L3 in the second dimension is done in the spatial domain. The integers K1, K2, K3, L1, L2, L3 are chosen so the (K1K2/K3)=R, (L1L2/L3)=S, (K1/P).gtoreq.R, (L1/Q).gtoreq.S, and the ratios (K2/K3) and (L1/L2) are close to 1. The inequality constraints guarantees that the inverse DCT process does not remove low-frequency components that should be present in in image scaled down by factors R, S. The conditions that the ratios K2/K3 and L2/L3 be close to 1 are imposed so that the scaling procedure be simple (fast) to implement. Typically, but not necessarily, P=Q, R=S, K1=L1, K2=L2, K3=L3.
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Feig Ephraim
Finlay Ian Richard
Linzer Elliot Neil
Au Amelia
International Business Machines - Corporation
Morris Daniel P.
Prikockis Larry J.
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