Search results for "Color difference"
showing 10 items of 20 documents
An adaptive-PCA algorithm for reflectance estimation from color images
2008
This paper deals with the problem of spectral reflectance estimation from color camera outputs. Because the reconstruction of such functions is an inverse problem, stabilizing the reconstruction process is highly desirable. One way to do this is to decompose reflectance function on a basis functions like PCA. The present work proposes an algorithm making PCA adaptive in reflectance estimation from a color camera output. We propose to adapt the PCA basis derivation by selecting, for each sample, the more relevant elements from the training set elements. The adaptivity criterion is achieved by a likelihood measurement. Finally, the spectral reflectance estimation results are evaluated with th…
Influence of resin cement shade on the color and translucency of zirconia crowns
2020
Background Zirconia crowns are highly attractive for clinicians, although have poor translucency when used as single restorations, in addition to unknown effect of resin cement shade on final cemented crown shade. This study aimed to assess effect of resin cement opacity on color replication potential of different zirconia frameworks with target tooth color, in addition to different zirconia crowns translucency evaluation. Material and methods Twenty-four zirconia crown restorations were fabricated to restore single central maxillary incisor for 8 patients, divided into 3 groups according to color and type of zirconia used (white Zr core, colored Zr core and monolithic HT Zrcowns). Each gro…
Perceptual similarity between color images using fuzzy metrics
2016
A method to measure the similarity between color images is proposed.Correlation among the color image channels is taken into account.Proposed similarity measure is based on fuzzy metrics because of their advantages.The proposal matches well with the perceptual visual similarity between color images. In many applications of the computer vision field measuring the similarity between (color) images is of paramount importance. However, the commonly used pixelwise similarity measures such as Mean Absolute Error, Peak Signal to Noise Ratio, Mean Squared Error or Normalized Color Difference do not match well with perceptual similarity. Recently, it has been proposed a method for gray-scale image s…
Application of the S-CIELAB color model to processed and calibrated images with a colorimetric dithering method.
2009
This work uses the S-CIELAB color model to compare images that have been calibrated and processed using a colorimetric dithering method which simulates increments in viewing distance. Firstly, we obtain XYZ calibrated images by applying the appropriate color transformations to the original images. These transformations depend on whether the image is viewed on a display device or encoded by a capture device, for example. Secondly, we use a colorimetric dithering method consisting of a partitive additive mixing of XYZ tristimulus values. The number of dithered pixels depends on simulated viewing distance. The dithered tristimulus values are transformed to digital data to observe the dithering…
On the uniform sampling of CIELAB color space and the number of discernible colors
2013
This paper presents a useful algorithmic strategy to sample uniformly the CIELAB color space based on close packed hexagonal grid. This sampling scheme has been used successfully in different research works from computational color science to color image processing. The main objective of this paper is to demonstrate the relevance and the accuracy of the hexagonal grid sampling method applied to the CIELAB color space. The second objective of this paper is to show that the number of color samples computed depends on the application and on the color gamut boundary considered. As demonstration, we use this sampling to support a discussion on the number of discernible colors related to a JND.
Colorimetric Characterization of Mobile Devices for Vision Applications
2015
Purpose: Available applications for vision testing in mobile devices usually do not include detailed setup instructions, sacrificing rigor to obtain portability and ease of use. In particular, colorimetric characterization processes are generally obviated. We show that different mobile devices differ also in colorimetric profile and that those differences limit the range of applications for which they are most adequate. Methods: The color reproduction characteristics of four mobile devices, two smartphones (Samsung Galaxy S4, iPhone 4s) and two tablets (Samsung Galaxy Tab 3, iPad 4), have been evaluated using two procedures: 3D LUT (Look Up Table) and a linear model assuming primary constan…
Multi-level contrast filtering in image difference metrics
2013
In this paper, we present a new metric to estimate the perceived difference in contrast between an original image and a reproduction. This metric, named weighted-level framework Δ E E (WLF-DEE), implements a multilevel filtering based on the difference of Gaussians model proposed by Tadmor and Tolhurst (2000) and the new Euclidean color difference formula in log-compressed OSA-UCS space proposed by Oleari et al. (2009). Extensive tests and analysis are presented on four different categories belonging to the well-known Tampere Image Database and on two databases developed at our institution, providing different distortions directly related to color and contrast. Comparisons in performance wi…
Freshness assessment of gilthead sea bream (Sparus aurata) by machine vision based on gill and eye color changes
2013
Abstract The fish freshness was evaluated using machine vision technique through color changes of eyes and gills of farmed and wild gilthead sea bream ( Sparus aurata ), being employed lightness ( L * ), redness ( a * ), yellowness ( b * ), chroma ( c * ), and total color difference (Δ E ) parameters during fish ice storage. A digital color imaging system, calibrated to provide accurate CIELAB color measurements, was employed to record the visual characteristics of eyes and gills. The region of interest was automatically selected using a computer program developed in MATLAB software. L * , b * , and Δ E of eyes increased with storage time, while c * decreased. The a * parameter of fish eyes…
Visual acuity and color discrimination in patients with cataracts.
2020
Color vision tests can give information about pathological changes in eye structures. The purpose of our research was to study the color vision sensitivity and visual acuity changes before and after cataract surgery. We used a saturated Farnsworth D15 color vision arrangement test to check color sensitivity changes in confusion line directions. The test is easily perceptible (essential to eldery patients), and it is possible to check color sensitivity changes in tritan, protan, and deutan confusion line directions. The results were analyzed in several ways: by summing the color differences between adjacent caps according to Bowman and averaging the color difference vectors according to Ving…
Color memory matching in normal and red-green anomalous trichromat subjects
2001
The methods of simultaneous and successive color matching have been studied for a set of seven color reference samples by 15 protanomalous and 21 deuteranomalous trichromat subjects. From comparison between both populations and a group of 25 trichromat normal ones, investigated previously under similar experimental conditions [J. Perez–Carpinell et al. Color memory matching: time effect and other factors. Color Res Appl 1998;23:234–247], we can deduce the following. (a) For anomalous trichromat populations, as with a normal one, we find significant differences between simultaneous and successive color matching, p < 0.05. (b) If we consider the average of all the colors, we find that, while …