In this paper, we present a novel method for inverse filtering a two dimensional (2-D) signal using phase-based processing techniques. A 2-D sequence can be represented by a sufficient number of samples of the phase of its Fourier transform and its region of support. This is exploited to perform deconvolution. We examine the effects of additive noise and incomplete knowledge of the point spread function on the performance of this deconvolution method and compare it with other 2-D deconvolution methods. The problem of finding the region of support will also be brie y addressed. Finally, an application example will be presented.
In the Differential Pulse-code Modulation (DPCM) image coding, the intensity of a pixel is predicted as a linear combination of a set of surrounding pixels and the prediction error is encoded. In this paper, we propose the adaptive residual DPCM (ARDPCM) for intra lossless coding. In the ARDPCM, intra residual samples are predicted using adaptive mode-dependent DPCM weights. The weights are estimated by minimizing the Mean Squared Error (MSE) of coded data and they are synchronized at the encoder and the decoder. The proposed method is implemented on the High Efficiency Video Coding (HEVC) reference software. Experimental results show that the ARDPCM significantly outperforms HEVC lossless coding and HEVC with the DPCM. The proposed method is also computationally efficient.
When interlaced scan (IS) is used for television transmission, the received video must be deinterlaced to be displayed on
progressive scan (PS) displays. To achieve good performance, the deinterlacing operation is typically computationally
expensive. We propose a receiver compatible approach which performs a deinterlacing operation inexpensively, with
good performance. At the transmitter, the system analyzes the video and transmits an additional low bit-rate stream.
Existing receivers ignore this information. New receivers utilize this stream and perform a deinterlacing operation
inexpensively with good performance. Results indicate that this approach can improve the digital television standard in a
receiver compatible manner.
Block-based image and video coding systems are used extensively in practice. In low bit-rate applications, however, they suffer from blocking artifacts. Reduction of blocking artifacts can improve visual quality and PSNR. Most methods in the literature that are proposed to reduce blocking artifacts apply post-processing techniques to the compressed image. One major benefit of such methods is no modification to current encoders. In this paper, we propose an approach where blocking artifacts are reduced using side information transmitted by the encoder. One major benefit of this approach is the ability to compare the processed image directly with the original undegraded image to improve the performance. For example, we could process an image with different methods and transmit the most effective method as part of the side information. A major question in using our proposed approach and compare it with a post-processing type of system and illustrate that the proposed approach has the potential to be beneficial in both visual quality and PSNR for some range of coding bit-rates.
Multiple description video coding is one method that can be used to reduce detrimental effects caused by transmission over lossy packet networks. In a multiple description system, a video sequence is segmented into two or more complimentary streams in such a way that each stream is independently decodable. When combined, the streams provide the highest level of quality, yet if one of the streams is lost or delivered late the video can be played out with only a slight reduction in overall quality. Each approach to multiple description coding consists of a tradeoff between compression efficiency and robustness. How efficiently each method achieves this tradeoff depends on the level of quality and robustness desired and on the characteristics of the video itself. Previous approaches to multiple description coding have made the assumption that a single segmentation method would be used for an entire sequence. Yet, the optimal method of segmentation can vary depending on the goals of the system, it can change over time, and it can vary within a frame. This work introduces a unique approach to multiple description coding through the use of adaptive segmentation. By selecting from a set of segmentation methods, the system adapts to the local characteristics of the video and maximizes tradeoff efficiency. We present an overview of this system and analyze its performance on real video sequences.
The enhancement layer in many scalable coding algorithms is composed of residual coding information. There is another type of information that can be transmitted instead of (or in addition to) residual coding. Since the encoder has access to the original sequence, it can utilize adaptive format conversion (AFC) to generate the enhancement layer and transmit the different format conversion methods as enhancement data. This paper investigates the use of adaptive format conversion information as enhancement data in scalable video coding. Experimental results are shown for a wide range of base layer qualities and enhancement bitrates to determine when AFC can improve video scalability. Since the parameters needed for AFC are small compared to residual coding, AFC can provide video scalability at low enhancement layer bitrates that are not possible with residual coding. In addition, AFC can also be used in addition to residual coding to improve video scalability at higher enhancement layer bitrates. Adaptive format conversion has not been studied in detail, but many scalable applications may benefit from it. An example of an application that AFC is well-suited for is the migration path for digital television where AFC can provide immediate video scalability as well as assist future migrations.
In conventional bit rate control schemes, the buffer level is controlled by adjusting the quantization step size while the frame rate and spatial resolution chosen for coding are fixed throughout the coding process. In this paper, we consider a more general Multidimensional (M-D) bit rate control where the frame rate, spatial resolution and quantization step size are jointly adapted for buffer control. In the M-D bit rate control setting, the problem is to decide which frames to code (and which frames to skip) along with the spatial resolution and the quantization step size to use for each coded frame. Given a finite set of operating points on a M-D grid, we formulate the optimal solution of the M-D buffer-constrained allocation problem. The formulation allows a skipped frame to be reconstructed from one coded frame using any temporal interpolation method. A dynamic programming algorithm is presented to obtain an optimal solution for the case of intraframe coding which is a special case of dependent coding. We experiment with both zero-order hold and motion-compensated temporal interpolation. Operational rate-distortion (R-D) bounds are illustrated for both the M-D and conventional bit rate control approaches. Our focus is one very low bit rate applications where a significant delay is tolerable.
In this paper, we propose a new method to improve the performance of a duplicate video transmission system. The proposed method is based on an alternate temporal sub-sampling approach, which is to transmit the encoded even-numbered and odd-numbered pictures through separate channels. At the receiver, the decoded pictures from both channels are combined by alternately choosing one from each channel. The proposed method uses the full capacity of both regular and backup channels for failure-free video transmission. Experimental results show that the proposed alternate temporal sub-sampling method gives about 1.0 to approximately 4.0 dB improvements in PSNR over the conventional simulcast one at the bit rates of 2 to approximately 15 Mbps/channel for failure-free video transmission.
Block-based video coders rely on motion compensated block prediction for more data compression. With the introduction of video coding over packet-switched networks such as the Internet and the resulting packet loss that occurs on congested networks, coding mode selection for each macro- block is significant in determining the overall distortion on the decoded video sequence. In this work, we examine the problem of mode selection for macro-blocks in the presence of loss and a channel rate constraint. We present and evaluate several methods for mode selection that attempt to minimize perceptual distortion from packet loss. We formulate a simplified problem which is useful for gaining some insight, and present an efficient algorithm to finding an optimal solution.
An algorithm for methodically deriving rate-distortion points for transform coefficient selection schemes for images is presented. The idea is to iteratively generate a set of convex hulls from which a composite operational rate- distortion curve is derived. Although this approach can be used to generate optimal interior rate-distortion points, the complexity is high. A fast suboptimal approach is then proposed which is based upon a modified version of threshold selection. In the modified threshold selection algorithm, each transform block operates on a point along a non-convex rate-distortion curve which is generated from rank ordering of coefficients in the block. Simulations of this fast algorithm using finely quantized DCT coefficients from an image with separate coding of amplitudes and runlengths show that very good rate-distortion performance can be obtained. These simulations also suggest that the modified threshold selection curve tends to lie within the first few convex hulls generated from the composite shell method. The modified threshold selection algorithm provides a fast way for achieving good rate-distortion performance in transform coding systems.
Region-based coding schemes may yield considerable improvements in performance as compared to block-based schemes. A fundamental problem in region-based coding is to efficiently encode the interior of each region. This paper proposes two approaches for coding the interiors of arbitrarily-shaped regions. The first is an adaptive iterative scheme and the second is a matching pursuits-type scheme. A geometric interpretation of the problem is given to provide insight into these approaches and to compare their different properties and performances. A number of examples illustrate the performance of the previous and proposed approaches.
Broadcasting High Definition Television (HDTV) requires the transmission of an enormous amount of information within a highly restricted bandwidth. Adhering to the transmission constraints, channel errors are inevitable. This paper proposes error concealment techniques to remove subjective effects of transmission errors. Error concealment techniques for several data parameters transmitted for the compressed representation of HDTV are considered. Specifically, we address errors in motion vectors and DCT coefficients. The concealment techniques estimate the true value of the corrupted parameters by exploiting the spatial and temporal correlation within the image sequence. In general, the error concealment techniques are found to be extremely successful in removing degradations from the decoded image.