Ocular complications in contact lens wearers are usually graded by specialists using visual inspection and comparing with a standard reference. The standard grading scales consist of either a set of illustrations or photographs ordered from a normal situation to a severe complication. Usually, visual inspection based on comparison with standards yields results that may differ from one specialist to another due to contour conditions or personal appreciation, causing a lack of objectiveness in the assessment of an ocular disorder. We aim to develop a method for an objective assessment of two contact lens wear complications: conjunctiva hyperemia and papillary conjunctivitis. In this work, we start by applying different image processing techniques to two standard grading scales (Efron and Cornea and Contact Lens Research Unit-CCLRU grading scales). Given a set of standard illustrations or pictures, image pre-processing is needed to compare equivalent areas. Histogram analysis allows segmenting vessel and background pixel populations, which are used to determine features, such as total area of vessels and vessel length, in the measurement of contact lens effects. In some cases, the colour content of standard series can be crucial to obtain a correct assessment. Thus, colour image analysis techniques are used to extract the most relevant features. The procedure to obtain an automatic grading method by digital image analysis of standard grading scales is described.
A method to evaluate the discrimination capability of a camera to measure small color differences in the nearly neutral region is proposed. We focus on the camera's performance in the nearly neutral region of the color space because: it represents a challenge for the instrument (these colors entail a similar stimulation of the RGB channels) and, second, these colors concentrate industrial interest, particularly related to materials for clothing or decorating. The method proposed has two stages. Firstly, we determine the appropriate working conditions of the acquisition system (SONY DX-9100P camera). Secondly, we select two sets of matte Munsell samples, regularly distributed in the Hue circle with low Chroma and Values. These two sets of samples are the very pale color and the dark grayish color sets. Each selected chip is compared with all its nearest neighbors of the Munsell color system under D65 illumination. CIELAB and CIEDE2000 formulae is used to estimate color differences. All the color differences are separately evaluated in pairs by the camera and by a reference instrument (spectroradiometer Photo-Research PR-715). We test the reliability of the camera's performance by comparing the results obtained by both the camera and the spectroradiometer.
The use of the Laplacian operator to enhance grayscale images by edge sharpening is widely known. The discrete application of this operator is made by convolving a mask whose kernel computes the weighted differences between neighbor pixels. The operator was extended to color images by applying it to each R, G, B, component separately and combining the result to yield the enhanced color image. In this work we apply the Laplacian operator to a color image by computing color differences between neighbor pixels in the CIELAB (CIEDE2000) space. The perceptual channels of Luminance, Chroma and Hue are used to obtain the resulting enhanced color image. N4 and N8-neighborhoods are considered. The results are compared with those obtained using the RGB channels separately. Using the Laplacian based on color difference, we obtain improved edge sharpening and artifact reduction in the resulting image.
A method to evaluate the discrimination capability of a camera to measure small color differences in the very pale color region is proposed. The measurements obtained by the camera are compared with those obtained by a reference instrument (spectrophotometer). Such comparisons indicate the reliability of the camera for this colorimetric purpose. CIEDE2000 formula of the CIELAB system has been used for the estimation of color differences. The method is applied to an acquisition system composed by a commercial 3CCD color camera capturing under standard D65 illumination. The results for the very pale color set of Munsell matte chips show that the color differences obtained by the given camera are quite close to those measured by the spectrophotometer over the circle of hue.