양승준 교수

The histogram equalization (HE) is a widely used contrast enhancement method. But what is missing from the HE is a mechanism to control the rate of enhancement. The enhanced image always follows the uniform distribution. This paper presents a simple enhancement rate control mechanism for the HE. The gradient of the mapping function is controlled by putting constraints on the probability density function with the bin underflow (BU) and bin overflow (BO). The BUBO operation can provide the rate of

At low bit rates, image compression codecs based on overlapping transforms introduce spurious oscillations known as ringing artifacts in the vicinity of major edges. Unlike previous works, we present a maximum-likelihood approach to the ringing-artifact removal problem. Our approach employs a parameter estimation method based on the k-means algorithm with the number of clusters determined by a cluster-separation measure. The proposed algorithm and its simplified approximation are applied to JPEG

Block-wise processing of motion compensated interlaced-to-progressive conversion (MC-IPC) can cause spurious errors that degrade converted image quality significantly. This paper presents a novel IPC method based on motion adaptive IPC (MA-IPC) with its adaptation assisted by the motion compensation. The motion adaptation is performed with respect to a motion selected from a limited set based on the accuracy evaluated with a reduced and overlapped block. The use of the reduced and overlapped blo

A reduced reference picture quality measure is proposed for MPEG-2 compressed videos. The measure can be calculated from the ratio of three N tap one-dimensional discrete cosine transform (DCT) coefficients. The proposed measures are highly correlated to subjective test scores and can provide accurate assessment of picture quality for a certain type of sequences.

This paper presents an image size conversion method based on bilateral filtering. We formulate interpolation with bilateral filters by an optimization problem, with which we can enforce the interpolation constraint as well as smoothness constraint. The designed bilateral filter can be used in image size conversion, providing better pass-band characteristics and less artifacts from aliasing.

At low bit rates, image compression codecs based on overlapping transforms introduce spurious oscillation known as ringing artifacts in the vicinity of major edges. The image quality can be enhanced considerably by removing the artifacts. We present a maximum likelihood approach to the ringing artifact removal problem. Our approach employs a parameter estimation method based on the k-means algorithm with the number of clusters determined by a cluster separation measure. The proposed algorithm an

This paper presents the generalized lapped biorthogonal transform embedded inverse discrete cosine transform (ge-IDCT) as an alternative to the IDCT. The ge-IDCT with nonlinear weighting in the embedded transform domain can reconstruct the signal with alleviated blockishness. Additional complexity, imposed by the replacement, is trivial thanks to an efficient lattice structure. The proposed ge-IDCT is applied in the JPEG still image compression standard to demonstrate its validity.

Motion compensated interlaced-to-progressive conversion (MC-IPC) methods employ implicit decision on whether to use the estimated motion vectors in order to prevent spurious errors due to poorly estimated motion vectors. This often limits the performance of the MC-IPC. We present an IPC method based on the pattern matching assisted motion estimation and motion vector histogram analysis. The proposed method employs an explicit decision on whether to use the estimated motion vectors. Extensive exp

Biased anisotropic diffusion is applied to the coding artifacts removal of the DCT based codec. It is formulated as a cost minimization problem. The weighting factors of the cost function are controlled such that the solution removes the blocking effect and conceals the block losses. It has an advantage over other postprocessing schemes because it handles the discontinuity of the image, smoothes the image selectively, and takes the visual masking in to account. Features needed for the weighting

The Gibbs distribution with spatially adaptive clique potential functions is used as the image prior distribution in the coding artifact reduction problem. Unlike previous approaches, the image is divided in regions based on the local statistics and a clique potential function is assigned for each region. A non-differentiable potential function that preserves edge in detailed image regions is introduced. Images recovered by the proposed approach contain reduced coding artifact and improved prese

Image/video size conversion at variable rates requires that a large set of interpolation filters should be stored in a table. We present the interpolated Mth-band filters as the interpolation filters, which are obtained from the cubic spline interpolation of a prototype M/sub p/th-band eigenfilter. The proposed filter can be calculated in real time, eliminating the need for a large on-chip memory. Scaled images using the proposed filters show superb image quality.

A particle filtering based block-wise estimation method for estimation of motion in a video sequence and joint estimation of disparity and motion in a stereo video sequence is proposed. Parameters of motion and disparity of a block in a sequence are defined as a state, and evolution of the state with respect to the block index is tracked with particle filtering. The state is assumed to be dependent on the states of neighboring blocks. Estimated motion and disparity fields are consistent and suit

In this paper, we extend the results of the denoising in the wavelet domain to the lapped transform (LT) domain. The LT coefficients are rearranged into the octave based representation, and their statistics are modeled by the same methods as the wavelet coefficients. Since the part of the LT that follows the discrete cosine transform (DCT) is orthogonal, the problem of removing the quantization noise introduced in the DCT based codecs can be solved in the LT domain. The maximum a posteriori (MAP