In this paper, we study the importance of pre-training for the generalization capability in the color constancy problem. We propose two novel approaches based on convolutional autoencoders: an unsupervised pre-training algorithm using a fine-tuned encoder and a semi-supervised pre-training algorithm using a novel composite-loss function. This enables us to solve the data scarcity problem and achieve competitive, to the state-of-the-art, results while requiring much fewer parameters on ColorChecker RECommended dataset. We further study the over-fitting phenomenon on the recently introduced version of INTEL-TUT Dataset for Camera Invariant Color Constancy Research, which has both field and non-field scenes acquired by three different camera models.
Typically, color constancy algorithms are divided into two main categories, namely unsupervised methods and supervised methods. The former involve methods with static parameters settings which are based on low-level statistics @cite_31 @cite_27 @cite_5 @cite_23 @cite_2 and methods using physics-based dichromatic reflection model @cite_21 @cite_1 @cite_18 @cite_24 , while the latter involve data-driven approaches that learn to estimate the illuminant in a supervised manner using labeled data. Supervised methods can be further divided into two main categories: characterization-based methods and training-based methods. The former involve characterization of camera response in one way or another, such as Gamut Mapping @cite_22 , which assumes that in a real world scenario, for a given illuminant, only a limited number of colors can be observed. The latter involve methods that try to learn illumination directly from the scene @cite_7 @cite_9 @cite_11 @cite_26 . One group of training-based methods considers different illumination estimation approaches and learns a model that uses the best performing method or a combination of methods to estimate the illuminant of each input based on certain scene characteristics @cite_26 . Another group of learning-based methods uses deep learning based approaches to solve the illumination estimation problem.
@cite_18 @cite_26 @cite_22 @cite_7 @cite_9 @cite_21 @cite_1 @cite_24 @cite_27 @cite_23 @cite_2 @cite_5 @cite_31 @cite_11
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In this work, we investigate how illuminant estimation techniques can be improved taking into account intrinsic, low level properties of the images. We show how these properties can be used to drive, given a set of illuminant estimation algorithms, the selection of the best algorithm for a given image. The algorithm selection is made by a decision forest composed of several trees on the basis of the values of a set of heterogeneous features. The features represent the image content in terms of low-level visual properties. The trees are trained to select the algorithm that minimizes the expected error in illuminant estimation. We also designed a combination strategy that estimates the illuminant as a weighted sum of the different algorithms' estimations. Experimental results on the widely used Ciurea and Funt dataset demonstrate the effectiveness of our approach. We present a novel image transform called Scale Manipulation (SMT). The transform can be used for object pose estimation and registration of affine transformed images in the presence of non homogenous illumination changes. The transform calculates affine invariant features of objects in a global manner and avoids using any sort of edge detection. The computational load of the method is relatively low since it is linear in the data size. In this paper we introduce the transform and demonstrate its applications for pose estimation in the presence of non uniform varying illumination. Computational color constancy is a fundamental prerequisite for many computer vision applications. This paper presents a survey of many recent developments and state-of-the-art methods. Several criteria are proposed that are used to assess the approaches. A taxonomy of existing algorithms is proposed and methods are separated in three groups: static methods, gamut-based methods, and learning-based methods. Further, the experimental setup is discussed including an overview of publicly available datasets. Finally, various freely available methods, of which some are considered to be state of the art, are evaluated on two datasets. Most video processing applications require object tracking as it is the base operation for real-time implementations such as surveillance, monitoring and video compression. Therefore, accurate tracking of an object under varying scene conditions is crucial for robustness. It is well known that illumination variations on the observed scene and target are an obstacle against robust object tracking causing the tracker lose the target. In this paper, a 2D-cepstrum based approach is proposed to overcome this problem. Cepstral domain features extracted from the target region are introduced into the covari-ance tracking algorithm and it is experimentally observed that 2D-cepstrum analysis of the target object provides robustness to varying illumination conditions. Another contribution of the paper is the development of the co-difference matrix based object tracking instead of the recently introduced covariance matrix based method. In this paper, the estimation of the illuminant in color constancy issues is analysed in two perceptual color spaces, and a variation of a well-known methodology is presented. Such approach is based on the Gray-World assumption, here particularly applied on the chromatic components in the CIELAB and CIELUV color spaces. A comparison is made between the outcomes on imagery for each color model considered. Reference images from the Gray-Ball dataset are considered for experimental tests. The performance of the approach is evaluated with the angular error, a metric well accepted in this field. The experimental results show that operating on perceptual color spaces improves the illuminant estimation, in comparison with the results obtained using the standard approach in RGB. There are several models for lightness computation, as many are the retinex based theories about color constancy. This paper provides a new hybrid technique for color recovery, which combines one of the most effective retinex algorithm (McCann99) and the gray world transformation applied at multiple resolutions.. A novel post processing step is also presented that improves the final color balance and range. The experimental tests on synthetic and real images, confirm the algorithm robustness and the improved color recovery capability with respect to other on the edge algorithms. In many multi-media applications it is desirable to separate the influence of the illumination sources and imaging equipment from the properties of the depicted scene. The ability of the human visual system to solve this task in many situations is known as color constancy. Technical applications of these methods include automatic color correction and illumination independent search in image databases. Many conventional computational color constancy methods assume that the effect of an illumination change can be described by a matrix multiplication with a diagonal matrix. In this paper we introduce a color normalization algorithm which computes the unique color transformation matrix which normalizes a given set of moments computed from the color distribution of an image. This normalization procedure is a generalization of the channel independent color constancy methods since general matrix transformations are considered. We compare the performance of this new normalization method with conventional color constancy methods. The experiments show that diagonal transformation matrices provide a better illumination compensation. This shows that the color moments also contain significant information about the color distributions of the objects in the image which is independent of the illumination characteristics. In another set of experiments we use the unique transformation matrix as a descriptor of the set of moments which describe the global color distribution in the image. Combining the matrices computed from two such images describes the color differences between them. We then use this as a tool for color dependent search in image databases. This matrix based color search is computationally less demanding than histogram based color search tools. Color constancy is the ability to measure colors of objects independent of the color of the light source. A well-known color constancy method is based on the gray-world assumption which assumes that the average reflectance of surfaces in the world is achromatic. In this paper, we propose a new hypothesis for color constancy namely the gray-edge hypothesis, which assumes that the average edge difference in a scene is achromatic. Based on this hypothesis, we propose an algorithm for color constancy. Contrary to existing color constancy algorithms, which are computed from the zero-order structure of images, our method is based on the derivative structure of images. Furthermore, we propose a framework which unifies a variety of known (gray-world, max-RGB, Minkowski norm) and the newly proposed gray-edge and higher order gray-edge algorithms. The quality of the various instantiations of the framework is tested and compared to the state-of-the-art color constancy methods on two large data sets of images recording objects under a large number of different light sources. The experiments show that the proposed color constancy algorithms obtain comparable results as the state-of-the-art color constancy methods with the merit of being computationally more efficient. Color equalization algorithms exhibit a variety of behaviors described in two differing types of models: Gray World and White Patch. These two models are considered alternatives to each other in methods of color correction. They are the basis for two human visual adaptation mechanisms: Lightness Constancy and Color Constancy. The Gray World approach is typical of the Lightness Constancy adaptation because it centers the histogram dynamic, working the same way as the exposure control on a camera. Alternatively, the White Patch approach is typical of the Color Constancy adaptation, searching for the lightest patch to use as a white reference similar to how the human visual system does. The Retinex algorithm basically belongs to the White Patch family due to its reset mechanism. Searching for a way to merge these two approaches, we have developed a new chromatic correction algorithm, called Automatic Color Equalization (ACE), which is able to perform Color Constancy even if based on Gray World approach. It maintains the main Retinex idea that the color sensation derives from the comparison of the spectral lightness values across the image. We tested different performance measures on ACE, Retinex and other equalization algorithms. The results of this comparison are presented.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. A neural network can learn color constancy, defined here as the ability to estimate the chromaticity of a scene’s overall illumination. We describe a multilayer neural network that is able to recover the illumination chromaticity given only an image of the scene. The network is previously trained by being presented with a set of images of scenes and the chromaticities of the corresponding scene illuminants. Experiments with real images show that the network performs better than previous color constancy methods. In particular, the performance is better for images with a relatively small number of distinct colors. The method has application to machine vision problems such as object recognition, where illumination-independent color descriptors are required, and in digital photography, where uncontrolled scene illumination can create an unwanted color cast in a photograph.