Preprocessing Technique for Face Recognition Applications under Varying illumination Conditions

In the last years, face recognition has become a popular area of research in computer vision, it is typically used in network security systems and access control systems but it is also useful in other multimedia information processing areas. Performance of the face verification system depends on many conditions. One of the most problematic is varying illumination condition. In this paper, we discuss the preprocessing method to solve one of the common problems in face images, due to a real capture system i.e. lighting variations. The different stages include gamma correction, Difference of Gaussian (DOG) filtering and contrast equalization. Gamma correction enhances the local dynamic range of the image in dark or shadowed regions while compressing it in bright regions and is determined by the value of 3B3;. DOG filtering is a grey scale image enhancement algorithm that eliminates the shadowing effects. Contrast equalization rescales the image intensities to standardize a robust measure of overall intensity variations. The technique has been applied to Yale-B data sets, Face Recognition Grand Challenge (FRGC) version 2 Experiment 4 and a real time created data set

Contrast enhancement and exposure correction using a structure-aware distribution fitting

Realce de contraste e correção de exposição são úteis em aplicações domésticas e técnicas, no segundo caso como uma etapa de pré-processamento para outras técnicas ou para ajudar a observação humana. Frequentemente, uma transformação localmente adaptativa é mais adequada para a tarefa do que uma transformação global. Por exemplo, objetos e regiões podem ter níveis de iluminação muito diferentes, fenômenos físicos podem comprometer o contraste em algumas regiões mas não em outras, ou pode ser desejável ter alta visibilidade de detalhes em todas as partes da imagem. Para esses casos, métodos de realce de imagem locais são preferíveis. Embora existam muitos métodos de realce de contraste e correção de exposição disponíveis na literatura, não há uma solução definitiva que forneça um resultado satisfatório em todas as situações, e novos métodos surgem a cada ano. Em especial, os métodos tradicionais baseados em equalização adaptativa de histograma sofrem dos efeitos checkerboard e staircase e de excesso de realce. Esta dissertação propõe um método para realce de contraste e correção de exposição em imagens chamado Structure-Aware Distribution Stretching (SADS). O método ajusta regionalmente à imagem um modelo paramétrico de distribuição de probabilidade, respeitando a estrutura da imagem e as bordas entre as regiões. Isso é feito usando versões regionais das expressões clássicas de estimativa dos parâmetros da distribuição, que são obtidas substituindo a mé- dia amostral presente nas expressões originais por um filtro de suavização que preserva as bordas. Após ajustar a distribuição, a função de distribuição acumulada (CDF) do modelo ajustado e a inversa da CDF da distribuição desejada são aplicadas. Uma heurística ciente de estrutura que detecta regiões suaves é proposta e usada para atenuar as transformações em regiões planas. SADS foi comparado a outros métodos da literatura usando métricas objetivas de avaliação de qualidade de imagem (IQA) sem referência e com referência completa nas tarefas de realce de contraste e correção de exposição simultâneos e na tarefa de defogging/dehazing. Os experimentos indicam um desempenho geral superior do SADS em relação aos métodos comparados para os conjuntos de imagens usados, de acordo com as métricas IQA adotadas.Contrast enhancement and exposure correction are useful in domestic and technical applications, the latter as a preprocessing step for other techniques or for aiding human observation. Often, a locally adaptive transformation is more suitable for the task than a global transformation. For example, objects and regions may have very different levels of illumination, physical phenomena may compromise the contrast at some regions but not at others, or it may be desired to have high visibility of details in all parts of the image. For such cases, local image enhancement methods are preferable. Although there are many contrast enhancement and exposure correction methods available in the literature, there is no definitive solution that provides a satisfactory result in all situations, and new methods emerge each year. In special, traditional adaptive histogram equalization-based methods suffer from checkerboard and staircase effects and from over enhancement. This dissertation proposes a method for contrast enhancement and exposure correction in images named Structure-Aware Distribution Stretching (SADS). The method fits a parametric model of probability distribution to the image regionally while respecting the image structure and edges between regions. This is done using regional versions of the classical expressions for estimating the parameters of the distribution, which are obtained by replacing the sample mean present in the original expressions by an edge-preserving smoothing filter. After fitting the distribution, the cumulative distribution function (CDF) of the adjusted model and the inverse of the CDF of the desired distribution are applied. A structure-aware heuristic to indicate smooth regions is proposed and used to attenuate the transformations in flat regions. SADS was compared with other methods from the literature using objective no-reference and full-reference image quality assessment (IQA) metrics in the tasks of simultaneous contrast enhancement and exposure correction and in the task of defogging/dehazing. The experiments indicate a superior overall performance of SADS with respect to the compared methods for the image sets used, according to the IQA metrics adopted

Automatic Segmentation of Optic Disc in Eye Fundus Images: A Survey

Optic disc detection and segmentation is one of the key elements for automatic retinal disease screening systems. The aim of this survey paper is to review, categorize and compare the optic disc detection algorithms and methodologies, giving a description of each of them, highlighting their key points and performance measures. Accordingly, this survey firstly overviews the anatomy of the eye fundus showing its main structural components along with their properties and functions. Consequently, the survey reviews the image enhancement techniques and also categorizes the image segmentation methodologies for the optic disc which include property-based methods, methods based on convergence of blood vessels, and model-based methods. The performance of segmentation algorithms is evaluated using a number of publicly available databases of retinal images via evaluation metrics which include accuracy and true positive rate (i.e. sensitivity). The survey, at the end, describes the different abnormalities occurring within the optic disc region

Complimentary Image Processing Techniques: Critical Review with C#

Image Enhancement is one of the most essential and laborious techniques in image researches. The scheme of image enhancement is to improve the visual semblance of an image, or to afford a “correct transform representation for future automated image processing. Many images like medical images, satellite images, aerial images and even real life photographs suffer from indigent contrast and noise. It is necessary to enhance the contrast and remove the noise to enhance image quality. One of the most significant stages in medical images detection and analysis is Image Enhancement techniques which improves the quality (clearness) of images for human look, removing blurring and noise, increasing contrast, and unveil details are examples of enhancement operations. The enhancement technique varies from one field to another according to its objective. The existent techniques of image enhancement can be classified into two categories: Spatial Domain and Frequency domain enhancement. In this research, we present an overview of image enhancement projection techniques in spatial domain. More specifically, we categorise processing methods based typical techniques of Image enhancement. Thus the contribution of this paper is to arrange and review image enhancement procedure techniques, attempt an evaluation of shortcomings and universal needs in this field of active research and in last we will stage out promising directions on research for image enhancement for prospective research. Keywords: Frequency based domain enhancement, Image Enhancement, Spatial based domain enhancement, Histogram Equalization

Enhancement of Gray Color Image using Limited Histogram Equalization Technique

Image enhancement plays asignificant role in multimedia and image processing applications. Many images writhe from poor dissimilarity and noise due to the insufficient lighting during image obtaining. So it is required to enhance the contrast of image as well as remove the noise that reductions image quality. The objective of enhancement is to improve the fundamental appearance of an image without any degradation in the input image. The main goal of this paper is to give a simple implementation of histogram equalization algorithm of a color image in efficient manner