Real-time Contrast Enhancement Research Articles

Rapid Prototyping of Image Contrast Enhancement Hardware Accelerator on FPGAs Using High-Level Synthesis Tools

Rapid prototyping tools have become essential in the race to market. In this work, we have explored employing rapid prototyping approach to develop an intellectual property core for real-time contrast enhancement which is a commonly employed image processing task. Specifically, the task involves real-time contrast enhancement of video frames, which is used to repair washed out (overexposed) or darkened (underexposed) appearance. Such scenario is frequently encountered in video footage captured underwater. Since the imaging conditions are not known a priori, the lower and upper limits of the dynamic range of acquired luminance values need to be adaptively determined and mapped to the full range permitted by the allocated bitwidth so that the processed image has a high-contrast appearance. This paper describes a hardware implementation of this operation using contrast stretching algorithm with the help of Simulink high-level synthesis tool using rapid prototyping paradigm. The developed model can be directly used as a drop-in module in larger computer vision systems to enhance Simulink computer vision toolbox capabilities, which does not support this operation for direct FPGA implementation yet. The synthesized core consumes less than 1% of total FPGA slice logic resources while dissipating only 7 mW dynamic power. To this end, look-up table has been employed to implement the division operator which otherwise requires exorbitantly large number of logic resources. Moreover, an online algorithm has been proposed which avoids multiple memory accesses. The hardware module has been tested in a real-time video processing scenario at 100 MHz clock rate and depicts functional accuracy at par with the software while consuming lower logic resources than competitive designs. These results demonstrate that the appropriate use of modern rapid prototyping tools can be highly effective in reducing the development time without compromising the functional accuracy and resource utilization.

Spatio‐temporal video contrast enhancement

A video contrast enhancement algorithm which automatically enhances the contrast of a video using spatial and temporal information is proposed. The algorithm is based on the observation that the contrast in a video frame can be improved by increasing the grey-level differences between each pixel of the video frame and its neighbouring pixels. Furthermore, such an improvement should be smooth in between consecutive video frames so that continuum of contrast improvement is achieved. A two-dimensional (2D) histogram of a video frame is constructed using mutual relationship between each pixel and its neighbouring pixels. For each video frame, a 2D target histogram is computed by considering 2D histogram of the video frame, 2D uniformly distributed histogram, and the 2D histograms of forward and backward neighbouring video frames. The contrast enhancement of the video frame is achieved by mapping the diagonal elements of the 2D input histogram to the diagonal elements of the 2D target histogram. The proposed algorithm is easy to implement and is thus suitable for real-time contrast enhancement applications.

Embedded system for contrast enhancement in low-vision

This paper presents a real-time contrast enhancement system, implemented in FPGA and adapted to display the processed images on a Head Mounted Display (HMD). A novel visual processing scheme is proposed which combines a version of the algorithm known as Contrast Limited Adaptive Histogram Equalization (CLAHE) with a spatial filtering based on a bio-inspired retina model. The system is designed so that visually impaired people can improve their functionality in environments with non-uniform lighting or with abrupt changes in lighting conditions. The parallelism offered by FPGA devices allow to achieve real-time processing with VGA-resolution images, reaching up to 60 frames per second. This system, developed on a FPGA of reduced complexity, has been compared in performance with a parallel implementation on a portable platform based on GPU.

Two-dimensional histogram equalization and contrast enhancement

In this paper, we propose a two-dimensional histogram equalization (2DHE) algorithm which utilizes contextual information around each pixel to enhance the contrast of an input image. The algorithm is based on the observation that the contrast in an image can be improved by increasing the grey-level differences between each pixel and its neighbouring pixels. The image equalization is achieved by assuming that for a given image, the modulus of the grey-level differences between pixels and their neighbouring pixels are equally distributed. The well-known global histogram equalization algorithm is a special case of 2DHE when contextual information is not utilized. 2DHE is easy to implement requiring only a small number of simple arithmetic operations and is thus suitable for real-time contrast enhancement applications. Experimental results show that 2DHE produces better or comparable enhanced images than several state-of-the-art algorithms. The only parameter in 2DHE which requires tuning is the size of the spatial neighbourhood support which provides the contextual information for a given dynamic range of the enhanced image. An automated parameter selection algorithm is also presented. The algorithm can be applied to a wide range of image types.

Real-time contrast enhancement to improve speech recognition.

An algorithm that operates in real-time to enhance the salient features of speech is described and its efficacy is evaluated. The Contrast Enhancement (CE) algorithm implements dynamic compressive gain and lateral inhibitory sidebands across channels in a modified winner-take-all circuit, which together produce a form of suppression that sharpens the dynamic spectrum. Normal-hearing listeners identified spectrally smeared consonants (VCVs) and vowels (hVds) in quiet and in noise. Consonant and vowel identification, especially in noise, were improved by the processing. The amount of improvement did not depend on the degree of spectral smearing or talker characteristics. For consonants, when results were analyzed according to phonetic feature, the most consistent improvement was for place of articulation. This is encouraging for hearing aid applications because confusions between consonants differing in place are a persistent problem for listeners with sensorineural hearing loss.

A real-time contrast enhancement algorithm for infrared images based on plateau histogram

In this paper, a new self-adaptive contrast enhancement algorithm based on plateau histogram equalization for infrared images is presented. By analyzing the histogram of image, the threshold value is got self-adaptively. This new algorithm can enhance the contrast of targets in most infrared images greatly. The new algorithm has very small computational complexity while still produces high contrast output images, which makes it ideal to be implemented by FPGA (Field Programmable Gate Array) for real-time image process. This paper describes a simple and effective implementation of the proposed algorithm, including its threshold value calculation, by using pipeline and parallel computation architecture. The proposed algorithm is used to enhance the contrast of infrared images generated from an infrared focal plane array system and image contrast are improved significantly. Theoretical analysis and other experimental results also show that it is a very effective enhancement algorithm for most infrared images.

P-35: Distinguished Poster Paper: MPEG-Based Image Enhancement for the Visually Impaired: Implementation on a General-Purpose PC Platform

A real-time contrast enhancement algorithm for MPEG was implemented, demonstrating that the concepts proposed by Kim & Peli (SID 2003) are computationally efficient enough to run on a general purpose PC. The application supports further research into the effectiveness of the technique for those with visual impairments.

Contrast enhanced and phase controlled stroboscopic additive fibre optic TV-holography for whole field out-of-plane vibration analysis

A new technique for real-time contrast enhancement and phase control of fringes in additive Stroboscopic TV-holography applied to out-of-plane vibration analysis and its implementation on a fibre-optic electronic speckle pattern interferometer (FOESPI) are presented. Synchronous Stroboscopic illumination, firing two pulses per object vibration period, is combined with simultaneous inter-pulse (high frequency) and inter-frame (low frequency) phase modulation in the reference arm of the ESPI yielding a sequence of frames (interferograms) that are grabbed and processed in real-time. With this technique both speckle and fringe phases are independently controlled by means of the parameters of modulation enabling speckle contrast inversion, as required to enhance the visibility of fringes by sequential subtraction, as well as dynamic fringe phase shifting to solve peakvalley ambiguities.