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The Extent of Metamer Mismatching

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-07
Abstract: 

Metamer mismatching refers to the fact that two objects reflecting light causing identical colour signals (i.e., cone response or XYZ) under one illunimation may reflect light causing non-identical colour signals under a second illumination_ As a consequence of metamer mismatching, two objects appearing the same under one illuminant can be expected to appear different under the second illunimant. To investigate the potential extent of metamer mismatching, we calculated the metamer mismatching effect for 20 Munsell papers and 8 pairs of illunimants (Logvinenko & Tokunaga, 20 11) using the recent method (Logvinenko, Funt, & Godau, 2012) of computing the exact metan2er mismatch volume boundary. The results show that metamer mismatching is very significant for some lights. In fact, metamer mismatching was found to be so significant that it can lead to the prediction of some paradoxical phenomena, such as the possibility of 20 objects having the same colour under a neutral ("white") light dispersing into a whole hue circle of colours under a red light, and vice versa.

Document type: 
Conference presentation
File(s): 

A Robust Hue Descriptor

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-11
Abstract: 

A hue descriptor based on Logvinenko’s illuminantinvariant object colour atlas [1] is tested in terms of how well it maps hues to the hue names found in Moroney’s Colour Thesaurus [2] [3] and how well it maps hues of Munsell papers to their corresponding Munsell hue designator. Called the KSM hue descriptor, it correlates hue with the central wavelength of a Gaussian-shaped reflectance function. An important feature of this representation is that the set of hue descriptors inherits the illuminate invariant property of Logvinenko’s object colour atlas. Despite the illuminant invariance of the atlas and the hue descriptors, metamer mismatching means that colour stimulus shift [4] can occur, which will inevitably lead to some hue shifts. However, tests show that KSM hue is robust in the sense that it is much more stable under a change of illuminant than CIELAB hue.

Document type: 
Conference presentation
File(s): 

Spectral Compression: Weighted Principal Component Analysis versus Weighted Least Squares

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2014-02
Abstract: 

Two weighted compression schemes, Weighted Least Squares (wLS) and Weighted Principal Component Analysis (wPCA), are compared by considering their performance in minimizing both spectral and colorimetric errors of reconstructed reflectance spectra. A comparison is also made among seven different weighting functions incorporated into ordinary PCA/LS to give selectively more importance to the wavelengths that correspond to higher sensitivity in the human visual system. Weighted compression is performed on reflectance spectra of 3219 colored samples (including Munsell and NCS data) and spectral and colorimetric errors are calculated in terms of CIEDE2000 and root mean square errors. The results obtained indicate that wLS outperforms wPCA in weighted compression with more than three basis vectors. Weighting functions based on the diagonal of Cohen’s R matrix lead to the best reproduction of color information under both A and D65 illuminants particularly when using a low number of basis vectors.

Document type: 
Conference presentation
File(s): 

Subspace-Clustering-Based Multispectral Image Compression

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2014-11
Abstract: 

This paper describes a subspace clustering strategy for the spectral compression of multispectral images. Unlike standard PCA, this approach finds clusters in different subspaces of different dimension. Consequently, instead of representing all spectra in a single low-dimensional subspace of a fixed dimension, spectral data are assigned to multiple subspaces having a range of dimensions from one to eight. For a given compression ratio, this tradeoff reduces the maximum reconstruction error dramatically. In the case of compressing multispectral images, this initial compression step is followed by lossless JPEG2000 compression in order to remove the spatial redundancy in the data as well.

Document type: 
Conference presentation
File(s): 

Gaussian Illuminants and Reflectances for Colour Signal Prediction

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2014-11
Abstract: 

An alternative to the von Kries scaling underlying the chromatic adaptation transforms found in colour appearance models such as CIECAM02 is suggested for predicting what the colour signal (e.g., XYZ) reflected from a surface under a first illuminant is likely to become when lit instead by a second illuminant. The proposed method, G2M, employs metameric Gaussian-like functions to model the illuminant and reflectance spectra. The method’s prediction is based on relighting the Gaussian-like reflectance spectrum with the second Gaussian-like illuminant. Tests show that the proposed G2M method significantly outperforms CIECAT02.

Document type: 
Conference presentation
File(s): 

Metamer Mismatch Volumes of Flat Grey

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2014-11
Abstract: 

Metamer mismatching refers to the fact that two objects reflecting light causing identical colour signals (i.e., cone response or XYZ) under one illumination may reflect light causing nonidentical colour signals under a second illumination. As a consequence of metamer mismatching, two objects appearing the same under the first illuminant can be expected to appear different under the second illuminant. Metamers of the flat grey reflectance (i.e., 50% across the visible spectrum) are of particular interest since they show the potential seriousness of metamer mismatching. Metamer mismatching of flat grey is very significant for some lights and includes the possibility of 20 objects having the same colour signal as flat grey under red light dispersing into a whole hue circle under a neutral (“white”) light. Flat grey under LED illumination is also shown to have a significant metamer mismatch volume when the light is changed to D65.

Document type: 
Conference presentation
File(s): 

How Multi-Illuminant Scenes Affect Automatic Colour Balancing

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-05
Abstract: 

Many illumination-estimation methods are based on the assumption that the imaged scene is lit by a single course of illumination; however, this assumption is often violated in practice. We investigate the effect this has on a suite of illumination-estimation methods by manually sorting the Gehler et al. ColorChecker set of 568 images into the 310 of them that are approximately single-illuminant and the 258 that are clearly multiple-illuminant and comparing the performance of the various methods on the two sets. The Grayworld, Spatio-Spectral-Statistics and Thin-Plate-Spline methods are relatively unaffected, but the other methods are all affected to varying degrees.

Document type: 
Conference presentation
File(s): 

Metamer Mismatching as a Measure of the Color Rendering of Lights

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-05
Abstract: 

We propose a new method for evaluating the colour rendering properties of lights. The new method uses the degree of metamer mismatching for the CIE XYZ corresponding to flat grey (constant reflectance of 0.5) quantified in terms of the metamer mismatch volume index proposed by Logvinenko et al. (Logvinenko 2014). A major advantage of this method is that unlike many previous color rendering indices it does not depend on the properties of a chosen set of representative test objects.

Document type: 
Conference presentation
File(s): 

Comparing Colour Camera Sensors Using Metamer Mismatch Indices

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-05
Abstract: 

A new method of evaluating the colorimetric accuracy of a color camera is proposed that is based on the size (appropriately normalized) of the metamer mismatch volume induced by a change of 'observer' from camera to human eye and vice-versa. The degree of metamer mismatching indicates the range in the discrepancy of the colour signals that can arise and as such is a more well-founded measure of colorimetric accuracy than traditional spectral-based measures such as the root mean squared difference in fit between the camera and eye's sensitivity functions.

Document type: 
Conference presentation
File(s): 

Robust Chroma and Lightness Descriptors

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-10
Abstract: 

New descriptors for lightness and chroma are presented that are based on properties of a wraparound Gaussian metameric to the given XYZ tristimulus coordinates. For the 1600 samples of the Munsell glossy set, both descriptors are found to correlate to Munsell value and chroma at least as well as the corresponding CIECAM02 descriptors when the Munsell samples are under the CIE C illuminant. However, when the illuminant is changed the new descriptors were found to be considerably more consistent under the second illuminant than those of CIECAM02.

Document type: 
Conference presentation
File(s):