Analysis of colour channel coupling from a physics-based viewpoint: Application to colour edge detection

The Dichromatic Reflection Model (DRM) introduced by Shafer in 1985 is surely the most referenced physics-based model of image formation. A preliminary analysis of this model derives in the conclusion that colour channels remain coupled by the reflectance of objects surface material. Taking this observation as a basis, this paper shows that this coupling manifests itself at the signal level in the form of a set of properties only satisfied in uniform reflectance areas. Such properties are deeply analysed and formalized throughout the paper, and, eventually, they are stated geometrically. As will be seen, a compatibility relationship stems from this geometric interpretation, which allows checking at a very low cost whether two pixels correspond to the same scene reflectance or not. Finally, an edge detector based on the use of the previous relationship is presented as an example of application. This edge detector inherits all the properties of the compatibility relationship: simplicity, low computational power requirements, sensor noise adaptivity and insensitivity to image intensity changes due to scene objects curvature.     

Influence of drug colour on perceived drug effects and efficacy

A drug’s physical characteristics, such as colour, could be factors influencing its therapeutic effects. It is not well understood whether people’s expectations on drug effects and efficacy are affected by colour, especially among Chinese population. This study was conducted to examine people’s expectations on drug effects and efficacy on the basis of drug colour, and to reveal possible gender differences in colour-related drug expectations. Participants (n = 224) were asked to classify seven single-coloured and six two-coloured capsules into one of four categories of drug effects, and to indicate the strength of drug efficacy. It is found that all the coloured capsules yielded non-chance distributions in classifications of drug effects, with six single-coloured and four two-coloured capsules associated with specific drug effects. Colour also conveyed differential strengths of drug efficacy in general and in relation to specific drug effects. There were gender differences in drug expectations for some colours and colour combinations.

Practitioner Summary: Drug colour was found to have impacts on perceived drug effects and efficacy. The findings from the present study can be used by ergonomics practitioners to design appropriate drug colours in support of drug differentiation, therapeutic effects and medication adherence.     

The effect of text and background colour on visual search of Web pages

Usability and visual impact in Web pages are not necessarily compatible ideals. This paper investigates the effect of colour on the presentation of information in a navigation bar, and aims to contribute towards design guidelines for the use of colour on the Web. We studied the effect of the combination of text and background colour on visual search performance and subjective preference. Twenty-nine participants carried out a visual search task using mock Web pages. Analysis showed that higher contrasts between text and background colour led to faster searching and were rated more favourably. The results are discussed in terms of visual search processes and design recommendations are given.     

The influence of colour on CRT reading performance and subjective comfort under operational conditions

Performance and reports of comfort when proof-reading text displayed on a CRT were investigated as a function of the text/background colour. Luminances were those typically produced by commercially available hardware and software, and task conditions were designed to simulate those experienced by typical users. Colours from the extremes of the spectrum (red, blue) were shown to produce poorer reading performance, higher ratings of discomfort and a higher incidence of reported symptoms of discomfort than those from mid-spectrum and white stimulus conditions.     

Perceptual correction for colour grading of random textures

We present a method of colour shade grading for industrial inspection of random textures, the differences of which are at the threshold of human perception. This method uses image restoration techniques to recover an unblurred version of the image, and then blurs it the same way as the human visual system does, to emulate the process of the image being captured by the human sensor. Subsequently, the colour image is transformed into a perceptually uniform colour space, where colour gra ding takes place. Received: 10 October 1998 / Accepted: 21 March 2000     

The problems of environmental colour design in Japan

The streets of Japan have undergone a series of radical changes in aspect and appearance in the past century. Following the Imperial Restoration, rapid westernization took place, followed by overwhelming devastation during the Pacific War, 1939-1945. Early postwar Japan saw an abundance of cheap, unplanned construction. After that, an age of whirlwind economic development began, characterized by an explosion of neon and billboard advertisement, characterizing the new, competitive, business world. The streets of Japan, as a result, became what one might call areas of ‘colour noise pollution’. In 1981, Tokyo city buses painted in a loud and disconcerting combination of yellow and red appeared on the streets, putting ‘colour noise pollution’ at an all-time high. These unsightly vehicles led to the formation of the Study Group for Colour Use in Public Places (SCPP), composed of volunteers and members of the Japan Colour Research Institute. From this beginning, the SCPP has recognized two major challenges: tackling existing cases of ‘colour noise pollution’, e.g., neon signs and shops painted in fluorescent colours; and promoting improvement in potential sources of problems such as outdoor neon and billboard advertising, or automatic vending machines, which can lead to colour pollution. The purpose of this movement is to improve the overall Japanese urban environment from the point of view of colour.     

Accurate optical flow computation under non-uniform brightness variations

In this paper, we present a very accurate algorithm for computing optical flow with non-uniform brightness variations. The proposed algorithm is based on a generalized dynamic image model (GDIM) in conjunction with a regularization framework to cope with the problem of non-uniform brightness variations. To alleviate flow constraint errors due to image aliasing and noise, we employ a reweighted least-squares method to suppress unreliable flow constraints, thus leading to robust estimation of optical flow. In addition, a dynamic smoothness adjustment scheme is proposed to efficiently suppress the smoothness constraint in the vicinity of the motion and brightness variation discontinuities, thereby preserving motion boundaries. We also employ a constraint refinement scheme, which aims at reducing the approximation errors in the first-order differential flow equation, to refine the optical flow estimation especially for large image motions. To efficiently minimize the resulting energy function for optical flow computation, we utilize an incomplete Cholesky preconditioned conjugate gradient algorithm to solve the large linear system. Experimental results on some synthetic and real image sequences show that the proposed algorithm compares favorably to most existing techniques reported in literature in terms of accuracy in optical flow computation with 100% density.     

The effects of ambient illumination and target luminance on colour coding in a CRT display

In this paper, the effects of absolute colour-identification on a CRT display are compared under different experimental conditions, i.e., ambient illuminant intensity, colour temperature and target luminance. The results indicate that performance of colour identification deteriorated as ambient illuminant intensity was increased. Colour identification under the 2800 K colour temperature was better than that under the 1800 K and 5800K. Performance at high luminance was superior to that at low luminance. Colours were chosen to make up the colour coding system on the CRT display under various ambient illuminant conditions. The number and range of the colours selected for the colour coding could be expanded by increasing the target luminance on the CRT display.     

Indexing chromatic and achromatic patterns for content-based colour image retrieval

In this paper, we present a method to represent achromatic and chromatic image signals independently for content-based image indexing and retrieval for image database applications. Starting from an opponent colour representation, human colour vision theories and modern digital signal processing technologies are applied to develop a compact and computationally efficient visual appearance model for coloured image patterns. We use the model to compute the statistics of achromatic and chromatic spatial patterns of colour images for indexing and content-based retrieval. Two types of colour images databases, one colour texture database and another photography colour image database are used to evaluate the performance of the developed method in content-based image indexing and retrieval. Experimental results are presented to show that the new method is superior or competitive to state-of-the-art content-based image indexing and retrieval techniques.     

Luminance adaptation transform based on brightness functions for LDR image reproduction

Tone mapping algorithms are used for image processing to reduce the dynamic range of an image to be displayed on low dynamic range (LDR) devices. The Retinex, which was developed using multi-scale and luminance-based methods, is one of the tone mapping algorithms for dynamic range compression, color constancy and color rendition. Retinex algorithms still have drawbacks, such as lower contrast and desaturation. This paper proposes a multi-scale luminance adaptation transform (MLAT) based on visual brightness functions for the enhancement of contrast and saturation of rendered images. In addition, the proposed algorithm was used to estimate the minimum and maximum luminance and a visual gamma function for local adapted viewing conditions. MLAT showed enhanced contrast and better color representation than the conventional methods in the objective evaluations (CIEDE200 and VCM).     

The use of colour in language syntax analysis

The use of colour to reflect the syntax of typed-in language statements can make a language processor much more user-friendly. This paper shows how colour has been used in MicroCODIL and suggests ways in which the approach could be applied to other systems.     

The extended marine underwater environment database and baseline evaluations

Images captured in underwater environments usually exhibit complex illuminations, severe turbidity of water, and often display objects with large varieties in pose and spatial location, etc., which cause challenges to underwater vision research. In this paper, an extended underwater image database for salient-object detection or saliency detection is introduced. This database is called the Marine Underwater Environment Database (MUED), which contains 8600 underwater images of 430 individual groups of conspicuous objects with complex backgrounds, multiple salient objects, and complicated variations in pose, spatial location, illumination, turbidity of water, etc. The publicly available MUED provides researchers in relevant industrial and academic fields with underwater images under different types of variations. Manually labeled ground-truth information is also included in the database, so as to facilitate the research on more applicable and robust methods for both underwater image processing and underwater computer vision. The scale, accuracy, diversity, and background structure of MUED cannot only be widely used to assess and evaluate the performance of the state-of-the-art salient-object detection and saliency-detection algorithms for general images, but also particularly benefit the development of underwater vision technology and offer unparalleled opportunities to researchers in the underwater vision community and beyond.     

Learning and surface boundary feedbacks for colour natural scene perception

Boundary detection and segmentation are essential stages in object recognition and scene understanding. In this paper, we present a bio-inspired neural model of the ventral pathway for colour contour and surface perception, called LPREEN (Learning and Perceptual boundaRy rEcurrent dEtection Neural architecture). LPREEN models colour opponent processes and feedback interactions between cortical areas V1, V2, V4, and IT, which produce top-down and bottom-up information fusion. We suggest three feedback interactions that enhance and complete boundaries. Our proposed neural model contains a contour learning feedback that enhances the most probable contour positions in V1 according to a previous experience, and generates a surface perception in V4 through diffusion processes. We compared the proposed model with another bio-inspired model and two well-known contour extraction methods, using the Berkeley Segmentation Benchmark. LPREEN showed better performance than two methods and slightly worse performance than another one.     

Real-time colour recognition in symbolic programming for machine vision systems

It is impossible to collect more than a tiny proportion of all of the possible examples of a given hue to form a training set for a machine that learns to discriminate colours. In view of this, it is argued that colour generelization is essential. Three mechanisms for learning colours, as defined by a human being, are described. One of these is based upon an idea developed by A.P. Plummer and is implemented in a commercial device known as the intelligent camera. This implementation can learn the characteristics of coloured scenes presented to it and can segment a video image in real-time. This paper presents four procedures that allow the range of colours learned by such a system to be broadened so that recognition is made more reliable and less prone to generating noisy images that are difficult to analyse. Three of the procedures can be used to improve colour discrimination, while a fourth procedure is used when a single and general colour concept has to be learned. Several experiments were devised to demonstrate the effectiveness of colour generelization. These have shown that it is indeed possible to achieve reliable colour discrimination / recognition for such tasks as inspecting packaging and fruit. A practical system based upon the intelligent camera and controlled by software written in PROLOG has been developed by the authors and is being used in a study of methods for declarative programming of machine vision systems for industrial applications.     

Electro‐optical transfer function preferences for LCD TVs: The effect of display brightness and surround illumination on preferred gamma

Abstract— Recent commercial liquid‐crystal‐display (LCD) televisions are larger and brighter than traditional televisions, thus impacting the viewing conditions in which they are viewed. These changes in viewing conditions may require different electro‐optical transfer functions (EOTFs) for LCD TVs than those for conventional TVs. Here, the way various EOTFs affect the preferred image quality of test images with changes in brightness and surround illumination conditions are examined. The first method used a gain, offset, and gamma (GOG) function with a range of gamma values, and the second method altered the intrinsic EOTFs. Image preference for the simulated EOTFs was determined using a paired‐comparison experiment for ten images. The first experiment took place in a darkened room at two display luminance levels. The results indicated that a gamma of 1.6 was most preferred overall although more so at a lower screen luminance level. In a second experiment, the procedure was repeated with a dim surround of 10% of the display's white point. With this surround, preference for a gamma value of around 1.6 at both screen luminance levels was more enhanced. These results indicated that image preference for different EOTFs is dependent on display luminance and that this dependence is maintained with a dim surround.     

The effect of data augmentation and network simplification on the image‐based detection of broccoli heads with Mask R‐CNN

In current practice, broccoli heads are selectively harvested by hand. The goal of our work is to develop a robot that can selectively harvest broccoli heads, thereby reducing labor costs. An essential element of such a robot is an image‐processing algorithm that can detect broccoli heads. In this study, we developed a deep learning algorithm for this purpose, using the Mask Region‐based Convolutional Neural Network. To be applied on a robot, the algorithm must detect broccoli heads from any cultivar, meaning that it can generalize on the broccoli images. We hypothesized that our algorithm can be generalized through network simplification and data augmentation. We found that network simplification decreased the generalization performance, whereas data augmentation increased the generalization performance. In data augmentation, the geometric transformations (rotation, cropping, and scaling) led to a better image generalization than the photometric transformations (light, color, and texture). Furthermore, the algorithm was generalized on a broccoli cultivar when 5% of the training images were images of that cultivar. Our algorithm detected 229 of the 232 harvestable broccoli heads from three cultivars. We also tested our algorithm on an online broccoli data set, which our algorithm was not previously trained on. On this data set, our algorithm detected 175 of the 176 harvestable broccoli heads, proving that the algorithm was successfully generalized. Finally, we performed a cost‐benefit analysis for a robot equipped with our algorithm. We concluded that the robot was more profitable than the human harvest and that our algorithm provided a sufficient basis for robot commercialization.     

The effect of VDU colour on visual fatigue in the fovea and periphery of the visual field

The effect of the display of a visual display unit (VDU) on visual fatigue was investigated using the critical flicker frequency (CFF) paradigm. The results indicate that fatigue, as measured by CFF, varied as the VDU colour and eccentricity changed in the visual field. It was found that blue and red, that is, both extremes of the visible spectrum, strongly caused visual fatigue in the visual field when compared to green and yellow, that is, the middle range of the visible spectrum. Furthermore, for yellow and blue, VDU signal fatigue tended to decrease as the distance from the fovea increased. whereas for red and green, it increased by up to 10° in the periphery and then tended to decrease. The results indicate that yellow and green cause less fatigue in the periphery and fovea, respectively.     

Automatic design support and image evaluation of two-coloured products using colour association and colour harmony scales and genetic algorithm

Colour plays a key role in determining a consumer’s response to a product’s appearance. Accordingly, this study proposes an automatic design support system which enables a designer either to emulate the colour scheme of a two-coloured product and then to determine its corresponding image perception, or to search for the two-colour combination which most closely meets the required image perception. The proposed system combines a gray theory-based colour-association evaluation method and a colour-harmony-based aesthetic evaluation method to design and evaluate different product-colour schemes. Since colour-harmony theories cannot be implemented directly using the additive primaries (i.e. R (Red), G (Green) and B (Blue)) used in most computer-based colour emulations, this study develops a RGB-based colour-association and colour-harmony measurement scheme to evaluate the image perception of a particular product-colour scheme. In an inverse process, a genetic algorithm is applied to search for the near-optimal colour combination which satisfies the specified product colour-association goal and achieves a high degree of colour harmony. Various case studies involving the design and evaluation of a two-coloured thermos flask are provided for illustration purposes to demonstrate the effectiveness of the proposed method.