A study of digital camera colorimetric characterisation based on polynomial modelling

The digital camera is a powerful tool to capture images for use in image processing and colour communication. However, the RGB signals generated by a digital camera are device-dependent, i.e. different digital cameras produce different RGB responses for the same scene. Furthermore, they are not colorimetric, i.e. the output RGB signals do not directly correspond to the device-independent tristimulus values based on the CIE standard colorimetric observer. One approach for deriving a colorimetric mapping between camera RGB signals and CIE tristimulus values uses polynomial modelling and is described here. The least-squares fitting technique was used to derive the coefficients of 3× n polynomial transfer matrices yielding a modelling accuracy typically averaging 1 Δ E units in CMC(1:1) when a 3× 11 matrix is used. Experiments were carried out to investigate the repeatability of the digitising system, characterisation performance when different polynomials were used, modelling accuracy when 8-bit and 12-bit RGB data were used for characterisation and the number of reference samples needed to achieve a reasonable degree of modelling accuracy. Choice of characterisation target and media and their effect on metamerism have been examined. It is demonstrated that a model is dependent upon both media and colorant and applying a model to other media/colorants can lead to serious eye-camera metamerism problems

Orientation to the sun by animals and its interaction with crypsis

1. Orientation with respect to the sun has been observed in a wide range of species and hasgenerally been interpreted in terms of thermoregulation and/or ultraviolet (UV) protection. For countershaded animals, orientation with respect to the sun may also result from the pres-sure to exploit the gradient of coloration optimally to enhance crypsis.2. Here, we use computational modelling to predict the optimal countershading pattern for anoriented body. We assess how camouflage performance declines as orientation varies using acomputational model that incorporates realistic lighting environments.3. Once an optimal countershading pattern for crypsis has been chosen, we determineseparately how UV protection/irradiation and solar thermal inflow fluctuate with orientation.4. We show that body orientations that could optimally use countershading to enhance crypsisare very similar to those that allow optimal solar heat inflow and UV protection.5. Our findings suggest that crypsis has been overlooked as a selective pressure on orientationand that new experiments should be designed to tease apart the respective roles of these different selective pressures. We propose potential experiments that could achieve this

A Study of Colour Rendering in the In-Camera Imaging Pipeline

Consumer cameras such as digital single-lens reflex camera (DSLR) and smartphone cameras have onboard hardware that applies a series of processing steps to transform the initial captured raw sensor image to the final output image that is provided to the user. These processing steps collectively make up the in-camera image processing pipeline. This dissertation aims to study the processing steps related to colour rendering which can be categorized into two stages. The first stage is to convert an image's sensor-specific raw colour space to a device-independent perceptual colour space. The second stage is to further process the image into a display-referred colour space and includes photo-finishing routines to make the image appear visually pleasing to a human. This dissertation makes four contributions towards the study of camera colour rendering. The first contribution is the development of a software-based research platform that closely emulates the in-camera image processing pipeline hardware. This platform allows the examination of the various image states of the captured image as it is processed from the sensor response to the final display output. Our second contribution is to demonstrate the advantage of having access to intermediate image states within the in-camera pipeline that provide more accurate colourimetric consistency among multiple cameras. Our third contribution is to analyze the current colourimetric method used by consumer cameras and to propose a modification that is able to improve its colour accuracy. Our fourth contribution is to describe how to customize a camera imaging pipeline using machine vision cameras to produce high-quality perceptual images for dermatological applications. The dissertation concludes with a summary and future directions

Characterisation of Implant Supported Soft Tissue Prostheses Produced with 3D Colour Printing Technology

The numbers of patients needing facial prostheses has increased in the last few decades due to improving cancer survival rates. The many limitations of the handmade prostheses together with rapid expansion of prototyping in all directions, particularly in producing human anatomically accurate parts, have raised the question of how to employ this technology for rapid manufacturing of facial soft tissue prostheses. The idea started to grow and the project was implemented based on CAD/CAM principles – additive manufacturing technology, by employing layered fabrication of facial prostheses from starch powder and a water based binder and infiltrated with a silicone polymer (SPIS). The project aimed to produce a facial prosthesis by using 3D colour printing, which would match the patient’s skin shade and have the desirable mechanical properties, through a relatively low cost process that would be accessible to the global patient community. This was achieved by providing a simple system for data capture, design and reproducible method of manufacture with a clinically acceptable material. The prosthesis produced has several advantages and few limitations when compared to existing products/prostheses made from silicone polymer (SP). The mechanical properties and durability were not as good as those of the SP made prosthesis but they were acceptable, although the ideal properties have yet to be identified. Colour reproduction and colour matching were more than acceptable, although the colour of the SPIS parts was less stable than the SP colour under natural and accelerated weathering conditions. However, it is acknowledged that neither of the two methods used represent the natural life use on patients and the deficiencies demonstrated in terms of mechanical properties and colour instability were partially inherent in the methodology used, as the project was still at the developmental stage and it was not possible to apply real life tests on patients. Moreover, deficiencies in mechanical and optical properties were probably caused by the starch present, which was used as a scaffold for the SP. Furthermore, a suitable retention system utilising existing components was designed and added to the prosthesis. This enabled the prosthesis to be retained by implants with no need for the addition of adhesive. This would also help to prolong the durability and life span of the prosthesis. The capability of the printer to produce skin shades was determined and it was found that all the skin colours measured fall within the range of the 3D colour printer and thereby the printer was able to produce all the colours required. Biocompatibility was also acceptable, with a very low rate of toxicity. However, no material is 100% safe and each material has a certain range of toxicity at certain concentrations. At this stage of the project, it can be confirmed that facial prostheses were successfully manufactured by using 3D colour printing to match the patient’s skin shade, using biocompatible materials and having the desirable mechanical properties. Furthermore, the technology used enabled prostheses to be produced in a shorter time frame and at a lower cost than conventional SP prostheses. They are also very lightweight, easier to use and possibly more comfortable for the patients. Moreover, this technology has the capability of producing multiple prostheses at the time of manufacture at reduced extra cost, whilst the data can be saved and can be utilised/modified for producing further copies in the future without having to going through all the steps involved with handmade prostheses. Based on the mechanical properties and colour measurements the prostheses will have a finite service life and the recommendation is that these prostheses will need replacing every 6 to 12 months, depending on how the patient handles and maintains the prostheses and whether the prosthesis is being used as an interim or definitive prosthesis. This was largely comparable to existing prostheses but without the time and cost implications for replacement. However, it is acknowledged that further investigations and clinical case studies are required to investigate the “real life” effect on the prostheses and to get feedback from the patients in order to make appropriate improvements to the mechanical properties and the durability of the prosthesis

An innovative digital workfl ow for the fabrication of a prosthetic ear: A case report

The aim of maxillofacial rehabilitation is to provide suitable prostheses for patients with oro-facial defects, and enable them to resume their roles in society. Recent advances in bionics and prosthetics have combined different techniques to help in the production of aesthetic and functional prostheses. Technology can now supplement the freehand sculpting skills of the clinician by capturing accurate images of the soft tissues from both the defect and non-defect areas, and using these to digitally recreate the desired templates. This case report describes the digital steps used to capture necessary data for the design and fabrication of an auricular template, and fi nal ear prosthesis. Results from this case study suggested that the digital method is: 1) more accurate; 2) less time-consuming than traditional methods; and 3) less invasive, and thus more accepted by patients

Skin Blood Perfusion and Oxygenation Colour Affect Perceived Human Health

Skin blood perfusion and oxygenation depends upon cardiovascular, hormonal and circulatory health in humans and provides socio-sexual signals of underlying physiology, dominance and reproductive status in some primates. We allowed participants to manipulate colour calibrated facial photographs along empirically-measured oxygenated and deoxygenated blood colour axes both separately and simultaneously, to optimise healthy appearance. Participants increased skin blood colour, particularly oxygenated, above basal levels to optimise healthy appearance. We show, therefore, that skin blood perfusion and oxygenation influence perceived health in a way that may be important to mate choice

Model facial colour appearance and facial attractiveness for human complexions

Human facial complexion has been a subject of great interest in many areas of science and technology including dermatology, cosmetology, computer graphics, and computer vision. Facial colour appearance conveys vital personal information and influences social interactions and mate choices as contributing factors to perceived beauty, health, and age. How various colour characteristics affect facial preference and whether there are cultural differences are not fully understood. On the other hand, facial colour appearance cannot be simply quantified by colour measurement. Facial colour perception is distinctive. The perceptual aspects of facial colour appearance haven’t been precisely investigated. The present study aims to better understand the human colour perception of facial complexions. Psychophysical experiments were carried out to assess facial colour preference and facial colour appearance, respectively. A set of facial images of real human faces were used and the colour was rigorously controlled in those experiments so that the facial colour appearance could be evaluated based on the realistic skin models. Experiments on colour preference provided a thorough assessment of the relationships between various facial colour characteristics and preference judgements and meanwhile revealed large cultural differences between Caucasian and Chinese populations. A useful and repeatable analytical framework for facial preference modelling was provided. This work contributes to the growing body of research using realistic skin models and highlights the importance of examining various colour cues utilized in facial preference evaluation. Experiments on colour appearance for the first time precisely measured the overall colour perception of facial appearance. New indices WIS, RIS, and YIS were developed to accurately quantify perceived facial whiteness, redness, and yellowness. The perceptual difference between the colour appearance of the face stimuli and the nonface stimuli was discovered. Taken together, the present study shed new light on how our visual system perceives and processes colour information on human faces

The influence of the skin colour on the perceived attributes

Skin colour data are important for many applications such as medical, imaging, cosmetics. The present study was aimed to collect a comprehensive skin colour database, and to study the impact of the skin colour on the variety of facial impression attributes. Although many researchers and engineers have collected skin data，few of them studied the skin colours to measure the same locations on a large number of subjects from different ethnic groups using the same colour measuring instruments. As for studying the impact of the skin colour on the visual perceptions, many studies investigated the impact of the skin colour on the attractiveness, health and youth. Limited previous studies investigated the impact of the skin colour on the other impression attributes. The present study was divided into two experiments, Experiments 1 and 2. Experiment 1 was to accumulate the skin colour database, named the Leeds Liverpool skin colour (LLSC). It included skin colours of 188 people from four ethnic groups (Caucasian, Oriental, South Asian and African) and both genders. Three colour measuring methods were used to accumulate the skin colour of each subject’s 10 locations including facial locations (forehead, cheekbone, cheek, nose tip, chin and neck) and body locations (the back of the hand, inner forearm, outer forearm and fingertip). The colour measuring methods included a tele-spectroradiometer (TSR), a spectrophotometer (SP) and a set of skin colour chart used as a visual aid. Also, a characterised digital camera controlled by an imaging system was used to collect facial images. Before the data collection, the short-term repeatability of different settings of the TSR and the SP on measuring human skin colour in vivo was determined. And this was used to settle the measurement protocols of the two instruments. The LLSC database was later used to investigate the skin colour distribution between ethnic groups, between genders, between measuring methods. A skin whiteness and blackness scales based on the CIELAB L* and Cab* scales in CIELAB was developed by referencing the vividness and depth formulae, which was developed by Berns (2000). It was found that these scales and CIELAB hue angle can describe well the property of skin colour of each ethnic group. Experiment 2 was to investigate the impact of the skin colour on the facial impression attributes. Based on the LLSC database, the gamut of skin colour was defined. Twenty-three attributes used to describe facial skin colours were accumulated. They were classified into two groups (appearance and impression). Two experiments were carried out on a monitor to understand the impact of the skin colour on the perceived facial impression attributes. The first experiment (Experiment 2.1) was to study the relationship between different attributes by 10 observers. The results showed that only four dimensions were required to describe skin facial colours, which were named Likeable, Sociable, Feminine and Youth. The health was also selected because the traditional Chinese medicine has interested in it. The second experiment (Experiment 2.2) was to scale facial images selected from two ethnic groups and both genders by using these five impression attributes by 24 Chinese observers. The experimental results showed that there were systematic patterns between the impression attributes and the whiteness and hue angle scales. There are some differences between these images for each impression. The ethnic group had an impact on the judgement, but the difference between the Oriental and Caucasian female images was limited. Finally, mathematical models were successfully developed to predict the impressions from the skin whiteness and hue angle data