Ekram Khan

Segment dependent dynamic multi-histogram equalization for image contrast enhancement

Histogram equalization (HE) method proved to be a simple and most effective technique for contrast enhancement of digital images. However it does not preserve the brightness and natural appearance of the images, which is a major drawback. To overcome this limitation, several Bi- and Multi-HE methods have been proposed. Although the Bi-HE methods significantly enhance the contrast and may preserve the brightness, the natural appearance of the images is not preserved as these methods suffer with the problem of intensity saturation. While Multi-HE methods are proposed to further maintain the brightness and natural appearance of images, but at the cost of contrast enhancement. In this paper, two novel Multi-HE methods for contrast enhancement of natural images, while preserving the brightness and natural appearance of the images, have been proposed. The technique involves decomposing the histogram of an input image into multiple segments based on mean or median values as thresholds. The narrow range segments are identified and are allocated full dynamic range before applying HE to each segment independently. Finally the combined equalized histogram is normalized to avoid the saturation of intensities and un-even distribution of bins. Simulation results show that, for the variety of test images (120 images) the proposed method enhances contrast while preserving brightness and natural appearance and outperforms contemporary methods both qualitatively and quantitatively. The statistical consistency of results has also been verified through ANOVA statistical tool. This work utilizes the concept of histogram equalization.It introduces the new concept of even expansion of histogram bins.More emphasis has been given on avoidance of intensity saturation problem.New full dynamic range allocation of narrow segments has been introduced.New normalization function has also been introduced.

Memory efficient set partitioning in hierarchical tree (MESH) for wavelet image compression

This paper presents a memory efficient version of set partitioning in hierarchical tree (SPIHT). The proposed coder termed as memory efficient SPIHT (MESH), uses a single re-usable list instead of three continuously growing linked lists as in conventional SPIHT. The list is re-initialized at the beginning of each bit-plane (coding pass) and is exhausted within that bit-plane itself. Another feature of the proposed coder is that it uses a single pass for each bit-plane by merging the sorting and refinement passes of conventional SPIHT together. The reinitialization of the list in each bit-plane makes the proposed coder inherently error resilient. The performance of the proposed coder is measured in terms of coding efficiency and the worst case memory requirements for list entries in each bit-plane. The performance comparison with SPIHT shows that the proposed algorithm results in 50-70% memory saving while retaining a coding efficiency comparable to SPIHT.

FrWF-Based LMBTC: Memory-Efficient Image Coding for Visual Sensors

After the successful development of JPEG2000, many state-of-the-art wavelet-based image coding algorithms have been developed. However, the traditional discrete wavelet transform (DWT) is implemented with memory intensive and time-consuming algorithms and, therefore, has very high system resource requirements. In particular, the very large requirement of memory poses a serious limitation for multimedia applications on memory-constrained portable devices, such as digital cameras and sensor nodes. In this paper, we propose a novel wavelet-based image coder with low memory requirements and low complexity that preserves the compression efficiency. Our encoder employs the fractional wavelet filter (FrWF) to calculate the DWT coefficients, which are quantized and encoded with a novel low memory block tree coding (LMBTC) algorithm. The LMBTC is a listless form of the wavelet block tree coding algorithm. Simulation results demonstrate that the proposed coder significantly reduces memory requirements and computational complexity and has competitive coding efficiency in comparison with other state-of-the-art coders. The FrWF combined with the LMBTC is, thus, a viable option for image communication over wireless sensor networks.

Physical layer unequal error protection of wavelet coded video using Hierarchical QAM

Unequal Error protection (UEP) of wavelet coded video is investigated using Hierarchical Quadrature Amplitude Modulation (HQAM). Based on the unequal sensitivity of coded bit stream against transmission errors, this paper investigates the properties of HQAM constellation to provide different degree of error protection to the coded bits having different degree of importance. This paper proposes an UEP scheme, performed at the physical layer using HQAM to protect higher priority (more sensitive) bits strongly without any additional bandwidth, but at the cost of increased errors in the lower priority (less sensitive) bits. The performance of the transmission system is evaluated under the Additive White Gaussian Noise (AWGN). Simulation results verify the improvements in the performance.

Optimized cross-layer unequal error protection for wireless video communication

Error control strategies to video bitstream are usually provided at different layers of the communication network. Optimizing the error control strategies at different layers independently leads to inefficient utilization of the resources. In this paper, a cross-layer strategy to optimally utilize the application and physical layer resources for unequal error protection (UEP) of wavelet coded scalable video is investigated. We propose a cross-layer optimized UEP scheme, combining optimal forward error correction (FEC) at application layer and hierarchical QAM (HQAM) at physical layer. A look-up table-based approach, to select optimal parameter values at both layers that maximizes the overall video quality for a given channel condition, is suggested. A wide range of video sequences of different degree of motion and texture are considered to design the look-up table. The major advantage of the look-up table based approach is the low computation complexity of the transmission system, which is one of the major issue in portable video communication devices. Simulation results show the proposed scheme outperforms other techniques comprehensively over a wide range of channel conditions.

Reliable transmission of wavelet-based scalable video over wireless networks using cross-layer approach

The conventional network layers are mainly designed for fixed networks and are not suitable to cope the challenges offered by the modern wireless networks. Moreover, certain functionalities can be implemented simultaneously in more than one layer. For example, unequal error protection (UEP) can be performed at the application layer, using forward error correction (FEC), but it is bandwidth inefficient. On the other hand, UEP can also be performed at the physical layer using hierarchical modulation to protect higher priority bits more strongly without any additional bandwidth, but at the cost of increased errors in the lower priority bits. The authors propose a cross-layer UEP approach to enhance reliability of scalable video by combining adaptive FEC at the application layer and hierarchical quadrature amplitude modulation (HQAM) at the physical layer. The idea is to slightly reduce the FEC protection of higher priority bits and increase the FEC protection of low-priority bits in such a fashion that the overall data rate at the application layer remains unchanged. The higher priority bits are additionally protected using HQAM at the physical layer. Simulation results show significant improvements in performance when the proposed scheme is used.

Unequal error protection (UEP) of wavelet coded video using multi-layered Hierarchical QAM

In this paper, the performance of unequal error protection (UEP) scheme for wavelet coded video using multi-layered 64-Hierarchical QAM (64-HQAM) is presented. Depending on the error sensitivity of coded video bitstream against channel errors, the bitstream is partitioned into multiple sub-streams. The most sensitive sub-stream is assigned highest protection while least sensitive are assigned lowest protection by adjusting the distance between points in the constellation diagram of HQAM. The performance of the communication system is evaluated for Additive White Gaussian Noise (AWGN) channel. The simulation results demonstrate that three-layer UEP provides increased Quality-of-Service (QoS) compared to level two-layer UEP.

Efficiently-mapped adaptive hierarchical QAM for reliable scalable video communication

This paper proposes an efficiently-mapped adaptive hierarchical QAM (AHQAM) scheme for unequal error protection (UEP) of embedded video bitstream. The coded bits of each frame are hierarchically partitioned into high priority (HP) and low priority (LP) substream, using two-staged partitioning strategy. Then pairs of stream blocks, one from each substream are selected judiciously to form symbols, which are modulated using HQAM with varying modulation parameter. The proposed scheme is generic in nature and can be applied to any scalable video bitstream. Simulations are performed with 16-AHQAM for AWGN channel and it is observed that the proposed scheme offers up to 7.2 dB improvement in quality of received video as compared to 16-HQAM.

Optimized unequal error protection of embedded video bitstream using adaptive-hierarchical QAM

In this paper, a reliable video communication system using adaptive Hierarchical QAM (HQAM) is designed to provide optimized unequal error protection (UEP) to embedded video bitstreams. Based on the relative importance of bits, video bitstream is partitioned into two priorities, namely High Priority (HP) and Low Priority (LP) substreams. Then, the optimal value of modulation (or hierarchical) parameter (α) of HQAM, which controls the relative error protection of these substreams, is selected from a pre-designed look-up table. The proposed system adapts itself by adapting the optimal α according to the varying channel condition, without changing the modulation level. This is in contrast to conventional WiMAX and LTE systems, in which dynamic switching among multiple modulations is used to adapt the varying channel conditions. This paper proposes HQAM with adaptive α as an alternative to the multiple modulation schemes. Moreover, for fixed average transmission power, receiver demodulates symbols without the knowledge of α. In order to further improve the video quality and to reduce the effects of erroneously received LP bits, the proposed system uses another level of adaptation, in which received LP bits are adaptively considered or discarded, before decoding the video, depending on the channel conditions (or optimized α). Simulation results show that proposed system can achieve significant improvement in the video quality compared to QAM based EEP scheme and non-adaptive HQAM.

Unequal error protection of embedded video bitstream with optimized FEC

In this paper, an optimized unequal error protection scheme using Forward Error Correction (FEC) for transmission of embedded video bitstream over AWGN channel is investigated. The scheme exploits the non-uniform importance and error sensitivity of the bits generated by the a wavelet video coder. Depending upon their importance in the reconstruction of the video, the bitstream is first divided into High Priority (HP) and Low Priority (LP) substreams. Then appropriate FEC is applied to these substreams to protect them against the channel errors. The optimal FEC parameters are searched using an offline optimization technique subject to constraint that end-to-end transmission distortion is minimized. A look-up table with optimal FEC parameters for wide range of channel conditions, is designed. Furthermore, this paper also argues that whether optimized UEP has any advantage over EEP for protection of embedded bitstream. This scheme is suitable for real-time video communication using portable devices which possess low processing capabilities and small battery power.