Predicting visible image degradation by colour image difference formulae

Abstract We carried out a CRT monitor based psychophysical experiment to investigate the quality of three colour image difference metrics, the CIEΔE ab equation, the iCAM and the S-CIELAB metrics. Six original images were reproduced through six gamut mapping algorithms for the observer experiment. The result indicates that the colour image difference calculated by each metric does not directly relate to perceived image difference

Optical skin assessment based on spectral reflectance estimation and Monte Carlo simulation

Optical non-contact measurements in general, and chromophore concentration estimation in particular, have been identified to be useful tools for skin assessment. Spectral estimation using a low cost hand held device has not been studied adequately as a basis for skin assessment. Spectral measurements on the one hand, which require bulky, expensive and complex devices and direct channel approaches on the other hand, which operate with simple optical devices have been considered and applied for skin assessment. In this study, we analyse the capabilities of spectral estimation for skin assessment in form of chromophore concentration estimation using a prototypical low cost optical non-contact device. A spectral estimation work flow is implemented and combined with pre-simulated Monte Carlo spectra to use estimated spectra based on conventional image sensors for chromophore concentrations estimation and obtain health metrics. To evaluate the proposed approach, we performed a series of occlusion experiments and examined the capabilities of the proposed process. Additionally, the method has been applied to more general skin assessment tasks. The proposed process provides a more general representation in form of a spectral image cube which can be used for more advanced analysis and the comparisons show good agreement with expectations and conventional skin assessment methods. Utilising spectral estimation in conjunction with Monte Carlo simulation could lead to low cost, easy to use, hand held and multifunctional optical skin assessment with the possibility to improve skin assessment and the diagnosis of diseases

Multispectral Image Capture Using a Tunable Filter

In this article we describe the experimental setup of a multispectral image acquisition system consisting of a professional monochrome CCD camera and a tunable filter in which the spectral transmittance can be controlled electronically. We have performed a spectral characterisation of the acquisition system taking into account the acquisition noise. To convert the camera output signals to device-independent data, two main approaches are proposed and evaluated. One consists in applying regression methods to convert from the # camera outputs to a device-independent colour space such as CIEXYZ or CIELAB. Another method is based on a spectral model of the acquisition system. By inverting the model using a Principal Eigenvector approach, we estimate the spectral reflectance of each pixel of the imaged surface. Keywords: Liquid Crystal Tunable Filter, spectral reflectance, multispectral imaging, spectral match, metamerism 1. INTRODUCTION Already in 1853 Grassmann stated that three variable..

A multispectral design for a new generation of film scanners

The digital reproduction of a historical motion picture should resemble as much as possible the analog film projection at the time of the movie release. Nowadays, practices of capturing digital images of films do not properly consider the fundamental elements and conditions of the original film projection. The typical rigid three-band (RGB) capture cannot adapt to the multitude of historical color film stocks to be digitized, and the diffuse illumination on the film generally used by standard digital scanning devices is unable to guarantee the proper visual rendition of the original analog projection of film prints. In order to overcome these problems, we designed and built a novel multispectral imaging system that illuminates the film with a condensed light beam. The new imaging system and the computational pipeline were tested on an assorted set of photographic colors. The accuracy of the multispectral captures was tested by comparison with corresponding spectrally resolved point-based radiometric measurements of the light reflected by a screen during analog projection. The presented optical design represents an excellent solution for the creation of a new multispectral motion picture scanner prototype. The LED-based illumination system coupled with a film transport mechanism can be the core concept of a promising new generation of motion picture film scanners

Image quality metrics for the evaluation of print quality

Image quality metrics have become more and more popular in the image processing community. However, so far, no one has been able to define an image quality metric well correlated with the percept for overall image quality. One of the causes is that image quality is multi-dimensional and complex. One approach to bridge the gap between perceived and calculated image quality is to reduce the complexity of image quality, by breaking the overall quality into a set of quality attributes. In our research we have presented a set of quality attributes built on existing attributes from the literature. The six proposed quality attributes are: sharpness, color, lightness, artifacts, contrast, and physical. This set keeps the dimensionality to a minimum. An experiment validated the quality attributes as suitable for image quality evaluation. The process of applying image quality metrics to printed images is not straightforward, because image quality metrics require a digital input. A framework has been developed for this process, which includes scanning the print to get a digital copy, image registration, and the application of image quality metrics. With quality attributes for the evaluation of image quality and a framework for applying image quality metrics, a selection of suitable image quality metrics for the different quality attributes has been carried out. Each of the quality attributes has been investigated, and an experimental analysis carried out to find the most suitable image quality metrics for the given quality attributes. For the many attributes metrics based on structural similarity are the the most suitable, while for other attributes further evaluation is required