Showing papers on "Contourlet published in 2001"

Pyramidal directional filter banks and curvelets

Abstract: A flexible multiscale and directional representation for images is proposed. The scheme combines directional filter banks with the Laplacian pyramid to provide a sparse representation for two-dimensional piecewise smooth signals resembling images. The underlying expansion is a frame and can be designed to be a tight frame. Pyramidal directional filter banks provide an effective method to implement the digital curvelet transform. The regularity issue of the iterated filters in the directional filter bank is examined.

Frame reconstruction of the Laplacian pyramid

Abstract: We study the Laplacian pyramid (LP) as a frame operator, and this reveals that the usual reconstruction is suboptimal. With orthogonal filters, the LP is shown to be a tight frame, thus the optimal linear reconstruction using the dual frame operator has a simple structure as symmetrical with the forward transform. For more general cases, we propose an efficient filter bank for reconstruction in the LP that is shown to perform better than the usual method. Numerical results indicate that gains of more than 1 dB are actually achieved.

Image enhancement using multiscale oriented wavelets

Abstract: We describe a novel method of enhancing image geometric features using the oriented wavelets introduced in our earlier work (see Yu-Ping Wang, IEEE Trans. Image Proc., vol.8, no.12, p.1757-71, 1999). The poor directional selectivity of the conventional 2D wavelet transform has been circumvented by using this class of oriented wavelets. By taking advantage of directional wavelet decomposition, both the directional and scale correlation information are utilized for enhancing salient structures in images. To remove phase dependence, a pair of quadrature filters are used. The proposed algorithm has been applied to chromosome image enhancement. Comparisons of this algorithm with other approaches are presented.

An Enlargement Method of Digital Images Based on Laplacian Pyramid Representation without Edge-Effect

Abstract: Since the enlargement of digital images is carried out by insertion of sample points, the Nyquist frequency of the enlarged image is naturally larger than that prior to enlargement. Hence, estimation of unknown higher-frequency components is required for enlargement of digital images. On the other hand, Laplacian pyramid representation is widely known as a layered expression of the images. Based on this Laplacian pyramid representation, the unknown higher-frequency components to be estimated at the time of enlargement of digital images correspond to the unknown higher-resolution Laplacian components. There is strong correlation between the Laplacian images at different layers. Specifically, the edge information spans several continuous layers as zero crossings and hence appears at the same location. Differences in the layers are recognized as differences in gradient near the zero crossing. In this paper, this property is directly used to provide a method of obtaining unknown higher-resolution Laplacian images from low-resolution Laplacian images (direct method). The results of enlargement by the direct method are particularly good in the smoothly varying parts of the images, but there are some difficulties in enlargement at the edges and of details. The paper proposes a hybrid method in which the direct method is combined with the method of Greenspan, with excellent enlargement results at edges and details, after the enlargement of images by estimation of the unknown higher-resolution Laplacian images as in the direct method. It is demonstrated by many application examples that this hybrid method is reasonably simple and is superior numerically and subjectively. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(6): 40–49, 2001