Muhammad Safdar

AT-SAFNAQ algorithm for power allocation in MC-CDMA system

A power allocation algorithm for projection matrix receiver based MC-CDMA system named Adaptive Threshold SAFNAQ (AT-SAFNAQ), has been proposed. SAFNAQ is a combination of frequency domain (FDPA) and eigenvector based (EBPA) power allocation algorithms. SAFNAQ algorithm does not optimize threshold value and it uses same threshold value over different channel realizations. In AT-SAFNAQ, the receiver has an extra unit compared to the receiver used in SAFNAQ algorithm. This extra unit optimizes threshold level adaptively. In accordance with optimum threshold value and the subcarrier gains, the feedback vector is sent to the transmitter for allocation of power. We have compared our results with no power allocation, FDPA, EBPA and SAFNAQ. Simulation results show that AT-SAFNAQ algorithm provides noticeable improvement in performance compared to the algorithms available in literature. We have generated testing bits at transmitter end, passed through Rayleigh fading channel to calculate BER performance of the system at receiver end to verify the results. Moreover, Variances of BER for different users are explored to show that in our system all the users have equal priority.

Obtaining Absolute Scene Luminance Using HDR Imaging

The absolute measure of scene luminance is needed in many applications, e.g., color image reproduction (especially outdoor), surveillance images, light appearance, and glare prediction. Currently, commercial luminance cameras are being used, which are very expensive and have limitations in dynamic range. An efficient and inexpensive method is needed to obtain absolute luminance of each of pixels in the scene. In the current study, a method was proposed to obtain absolute scene luminance (XYZ map) at each pixel using digital RGB camera and high dynamic range (HDR) imaging. The proposed model was calibrated using a tele-spectroradiometer (TSR) by means of average luminance at a small spot. A good match of results was obtained between TSR and the proposed method.

Extension of SAFNAQ algorithm for MC-CDMA using channel allocation

For future systems of wireless communication, multi-carrier code division multiple access (MC-CDMA) is becoming much attractive due to its high data rate and multiple access capability. Continuing our research on main issues of MC-CDMA, which mainly include power and channel allocation, here we have considered power allocation following the channel allocation to improve overall performance of the system. In the current work, adaptive sub-channel allocation scheme has been incorporated into SAFNAQ algorithm to improve bit error rate (BER) performance of MC-CDMA system. SAFNAQ is an algorithm for transmission power allocation in MC-CDMA system. A projection matrix receiver based MC-CDMA system has been considered. The Rayleigh fading channel was used for simulations. The SAFNAQ algorithm, cohesion of frequency domain power allocation (FDPA) and eigen vector based power allocation (EBPA) algorithms, allocates available transmission power to adaptively chosen strongest sub-carriers with respect to corresponding coefficients of power balance vector computed using EBPA algorithm. In adaptive sub-channel allocation, different sub-channels are allocation to different users on the base of channel state information (CSI). In sub-channel allocation module, sub-channels were divided into small groups. Number of sub-channels in each group was equal to the length of pseudo random codes used to gain multiple access capability. At most one user can be allocated to each group simultaneously and corresponding users desired power is allocated to sub-channels of that group in accordance with SAFNAQ algorithm. The system was simulated for different number of users and channel paths. Simulation results showed that usage of adaptive sub-channel allocation along with SAFNAQ algorithm improves the overall system bit error rate (BER) performance.

Performance Comparison of Uniform Color Spaces by Integrating into a Tone Mapping Operator

Typically, tone mapping operators are used to map luminance of high dynamic range (HDR) scenes to that of a displayable range. The goal of this study was to compare the performance of different uniform color spaces (CIELAB, ICTCP, and Jazbz) by integrating them into a tone mapping operator. The Contrast Limited Adaptive Histogram Equalization-based Tone Mapping Operator (CLAHE-TMO) was used here. For this purpose, the HDR radiance map of a given scene was first constructed from multiple exposures of the scene captured by using an ordinary RGB camera. The radiance map was then transformed to a uniform color space for the application of TMO on its lightness channel. A psychophysical experiment was conducted using pair comparison method to compare performance of different uniform color spaces. Tone mapped images were compared in four different contexts: preference, naturalness, contrast, and texture details. The experimental results are reported here.

A neural response-based model to predict discomfort glare from luminance image:

It is well known that one of the problems of the current method for discomfort glare evaluation, called the unified glare rating, is the non-uniform luminance of the glare source. This paper addresses this issue by considering the spatial contrast of luminance as a measure of non-uniformity. An image-based metric is proposed to evaluate discomfort glare by modeling the neural response of human vision. The model takes an absolute luminance image as input and predicts visual discomfort based on the spatial distribution of the luminance of the stimulus and the background. The developed model was tested to predict subjective glare ratings based on an experiment conducted using non-uniform LED sources with symmetric and asymmetric patterns of LEDs, and its performance was compared with the unified glare rating. As expected, the unified glare rating predictions correlated well with the subjective glare evaluations of luminaires with symmetric patterns of LEDs (as they appear less non-uniform) but not for those with asymmetric patterns. Results showed that the developed model, named the Neural Response-based Glare Model, gave similar performance to unified glare rating for symmetric patterns but outperformed UGR for asymmetric patterns of LEDs.

Calibration of 3D Images in Terms of Spectral Reflectance

Recently, 3D image processing has become widespread in the various applications such as medical, animation, and graphics communication. There exist a number of techniques to transform 2D images into 3D. The purpose of this study was to develop a set of procedure to achieve precise color reproduction in cross-media color reproduction for 3D images and to simulate images under different illuminants. A 3dMD® system was used to capture images of 3D objects. A polynomial model-based camera characterization was implemented. To further enhance the scope of research, different 3D images were transformed into the spectral images via two different methods, principal component analysis (PCA) and Wiener. The spectral images were then used to transform images under different illuminants. Finally, a simulation of the appearance of 3D images on a display under different illuminants was successfully achieved.

Digital Camera-Based Appearance Meter (AppMeter)

Currently, people use luminance or illuminance meters to measure illumination at different spots in a room to know the appearance. A more robust method is needed to measure the spatial distribution of light as the spot measurement-based methods do not correspond to visual perception. The current study was conducted to propose an instrumental method to measure the appearance. The CIE color appearance model CIECAM02 was modified and proposed as an imaging method to predict the appearance attributes from an RGB image. As brightness is a function of CCT and Duv according to the previous studies, CIECAM02 brightness formula was extended in the current study. Raw data and images from three different experiments were collected to test the model. The correlation between predictions of modified CIECAM02 and visual data was found statistically significant for three different experiments.

Test Criteria and Investigation of Uniform Color Spaces to Meet the Requirements of Future Imagery

The television and cinema industry has grown very rapidly during last few years and future displays will likely be able to cover high dynamic range (HDR) and wide color gamut (WCG). A uniform color space is desired that is suitable not only for efficient quantization but also for color volume mapping in HDR and WCG environment. A design goal for the next generation display is Rec.2020 which is the minimum requirement for future video encoding. There are a number of aspects which must be considered while developing a color space in order to meet the requirements of future imagery. Current study lists eight different criterions to test the ability of a color space to meet these requirements. After defining the testing criteria, this study investigated four different color spaces including CIELAB, CAM16-UCS, ICaCb, and recently proposed zICaCb. Results showed that zICaCb outperformed other spaces tested for most of the measures and gave similar performance for others.