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A web‐hosted online experiment was previously developed to find the visual difference between four reproduction gamuts using direct magnitude estimation (Proc. IS&T 29th Color and Imaging Conf, 2021:317–322). In order to increase the size of the data set, but without overburdening observers, a modular approach was adopted. The original methodology was therefore extended across 10 linked sub‐experiments to make comparisons between some 36 gamuts, which were designed to exhibit a variety of different gamut shapes, contrast ratios, and substrate colors within the constraints of a desktop display. In addition to each set of test images, a common normalization set was included in all sub‐experiments in order to adjust each observer's choice of modulus to a global average observer, and thus combine the results into a larger data set. Finally, an interval scale was inferred from the normalized magnitude data using a categorical judgment approach to calculate scale values. The fitted data revealed a power function close to a square‐root between the interval and magnitude scales. [ABSTRACT FROM AUTHOR]

Methods for estimating spectral reflectance from XYZ colorimetry were evaluated using a range of different types of training datasets. The results show that when a measurement dataset with similar primary colorants (and therefore having similar reflectance curves) are used for training, the RMSE errors and metameric differences under different illuminants are the lowest. This study demonstrates that, a training data can be mapped to represent spectral data for a group of print data based on matching material components (spectral similarity) with the test data, and obtain spectral estimates with satisfactory spectral and colorimetric outcomes. The findings suggest that using polynomial bases or colorimetric weighted bases with least squares fit produced estimated reflectances with low metameric mismatches under different illuminants. For the two best performing spectral estimation methods their ability to predict tristimulus values were assessed with tristimulus calculated using the measured reflectances and a destination illuminant. Their performances were also compared to the colour predictions obtained from different CATs and MATs under varying lighting conditions. The results show that a spectral estimation method with specific training dataset can serve as a good alternative to predict XYZ under different illuminants with reduced metameric mismatch i.e. they can be used as a material adjustment transform. These results finally help in proposing a spectral estimation workflow that can be integrated into colour management such that it is simple to implement, fast in processing, spectrally accurate with low metameric mismatch. [ABSTRACT FROM AUTHOR]

Bidirectional reflection distribution function (BRDF) is used to measure colour with gloss and surface geometry. In this paper, we aim to provide a practical way of reproducing the appearance of a 3D printed surface in 2.5D printing of any slope angle and colour in a colour-managed workflow as a means for softproofing. To account for the change in colour due to a change in surface slope, we developed a BRDF interpolation algorithm that adjusts the colour of the tristimulus values of the flat target to predict the corresponding colour on a surface with a slope. These adjusted colours are then used by the interpolated BRDF workflow to finally predict the colour parameters for each pixel with a particular slope. The effectiveness of this algorithm in reducing colour differences in 2.5D printing has been successfully demonstrated. We then finally show how all the components, slope colour adjustment method, interpolated BRDF parameters algorithm, and BRDF model encoded profiles using iccMAX are connected to make a practical appearance reproduction framework for 2.5D printing. [ABSTRACT FROM AUTHOR]

Grey balance plays an important role in determining the device values needed to reproduce colours which appear achromatic throughout the tonal range. However, complete observer adaptation to the media white rarely occurs, and these designated device values can still appear non-neutral. This poses a problem for cross-media reproductions, where a mismatch in neutral colours is often the most noticeable difference between them. This paper presents two related experiments which investigate a means of gaining better visual agreement between reproductions which have different background colours or media whites. The first quantifies the degree of adjustment (the degree of media relative transform) needed to make an appearance match between grey patches on a white background and on background colours of various hues and colourfulness. It was found that the degree of adjustment was near-linearly related to the luminance of the patch itself, with lighter patches requiring greater adjustment towards the background colour. Neither the hue nor the chroma of the patch's background had any significant effect on the underlying function. In the second experiment, this concept is applied to pictorial images on paper-coloured backgrounds. Three pixelwise rendering strategies were compared. In side-by-side viewing, the adaptive control of neutrals outperformed the media relative transform in all cases. Even for modest differences in paper colour (1Eab of 3), images with significant neutral content benefited from the adaptive approach. [ABSTRACT FROM AUTHOR]

The Helmholtz‐Kohlrausch (H‐K) effect is investigated in relation to light colors of every hue, including those typical of print substrate colors that might be simulated on a graphic arts display. A method of adjustment is used in conjunction with a soft‐proof setup, in which an achromatic stimulus is adjusted until it has the same lightness appearance as a set of test colors. Higher chroma colors are found to appear lighter than their metric L* would indicate. The H‐K effect is found to be quite strong in bluish colors, but negligible in yellowish colors, consistent with several previous studies. However, qualitative analysis reveals a peak H‐K effect in red‐magenta hues. We propose a modification to Fairchild and Pirrotta's existing H‐K lightness appearance function1 which addresses the peak in red hues, and which may prove beneficial in hue‐dependent applications. [ABSTRACT FROM AUTHOR]

Document forgeries that involve modification of the materials used, such as ink and paper, provide evidence of any malpractices being performed. Forensic specialists use different techniques to identify and classify these samples; however, the most preferred method is to use nondestructive techniques to avoid any potential damage to the original specimen under investigation. Hyperspectral imaging has already been explored in several application domains and used as a powerful method in forensic investigations to extract information about the materials under examination. To precisely classify the material information and utilize the hyperspectral imaging technique's potential, we probed the potential of some hybrid spectral similarity measures to classify different commonly used paper samples. A comparison of these methods is quantitatively presented in this article. Hybrid spectral similarity algorithms are tested on forensic analysis of paper data. We compared the classification capabilities of various hybrid spectral similarity algorithms on hyperspectral data of 40 different paper samples. The overall accuracy (OA), kappa K̂, Z‐score of kappa (ZK̂), and the 95% confidence interval of kappa (CI(K̂)) are used for comparison. The SID‐SAM and SID‐SCA produced an overall accuracy of 88% and 87%, respectively, which is highest among the hybrid spectral similarity measures tested. [ABSTRACT FROM AUTHOR]

The efficiency of a texture classification procedure depends on the color space in which it is performed. Classification in a perceptually meaningful space requires chromatic coordinates obtained from a calibrated acquisition setup. The authors assess the impact of camera calibration, within a generic color picture acquisition workflow, on the performance of a number of texture classification techniques. An image calibration pipeline is established and applied to a texture database, and the accuracy of the classification algorithms is evaluated for each step. The results show that the most significant step of the workflow is color rendering although the effect is relatively small. Hence precise scene-referred characterization of the raw data from an acquisition camera is not essential for most texture classification tasks. In addition, working with output-referred RGB data is likely to be adequate for the majority of classification tasks. [ABSTRACT FROM AUTHOR]

For a suspected forgery that involves the falsification of a document or its contents, the investigator will primarily analyze the document's paper and ink in order to establish the authenticity of the subject under investigation. As a non-destructive and contactless technique, Hyperspectral Imaging (HSI) is gaining popularity in the field of forensic document analysis. HSI returns more information compared to conventional three channel imaging systems due to the vast number of narrowband images recorded across the electromagnetic spectrum. As a result, HSI can provide better classification results. In this publication, we present results of an approach known as the t-Distributed Stochastic Neighbor Embedding (t-SNE) algorithm, which we have applied to HSI paper data analysis. Even though t-SNE has been widely accepted as a method for dimensionality reduction and visualization of high dimensional data, its usefulness has not yet been evaluated for the classification of paper data. In this research, we present a hyperspectral dataset of paper samples, and evaluate the clustering quality of the proposed method both visually and quantitatively. The t-SNE algorithm shows exceptional discrimination power when compared to traditional PCA with k-means clustering, in both visual and quantitative evaluations. [ABSTRACT FROM AUTHOR]

This article aims to investigate print quality in newspaper print, by considering the appropriate calibration standard and applying colour management. In particular, this article examines the colorimetric properties of eight Norwegian newspaper printing presses, to evaluate the relevant colour separation approach, either by applying custom separation profiles or by using an industry standard profile. The key method underlying the work described here relies on obtaining colour measurements to determine the repeatability of each participant in terms of colour differences. Furthermore, the variation between the eight newspaper printing presses and the variation according to the colorimetric values of the ISO 12647-3 standard are important parts of the quantitative evaluation. Based on the colour measurements two custom ICC profiles were generated and an industry standard profile 'ISOnewspaper26v4.icc' was also used. The first custom profile was generated using averaged colour measurement data set from a test print run, and the second using a data set averaged between measured data and the characterization data set 'IFRA26.txt' provided by IFRA. These three profiles were applied to four test images, which were then printed by the eight newspaper printing presses. A psychophysical experiment was carried out to determine the 'pleasantness' of the reproductions, which were produced using the three profiles. The results of the study show the performance of the appropriate profile, which is applied to the eight newspaper printing presses to obtain significant best print quality. Eventually the results demonstrate the fact that the print variations in colours between the eight printing presses are larger thanthe difference between the custom and the standard profiles. Hence, the print variations and not the profile selection may have determined the visual print quality. Therefore the study reveals the importance of adopting international standards and methods instead of using insufficiently defined house standards to preserve equal results among different newspaper printing presses. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011 [ABSTRACT FROM AUTHOR]

The stationarity of a texture can be considered a fundamental property of images, although the property of stationarity is difficult to define precisely. We propose a stationarity test based on multiscale, locally stationary, 2D wavelets. Three separate experiments were performed to evaluate the capabilities and the limitations of this test. The experiments comprised a chessboard stationarity analysis, two classification tasks, and a psychophysical experiment. The classification tasks were performed on 110 texture images from a texture database. In one subtask, five texture feature vectors were extracted from each image and the classification accuracy of two classical methods compared, whereas in the second subtask, the classification accuracy of several methods was compared to the descriptors defined for each image within the database. In the psychophysical experiment, the correlation between the classification results and observer judgements of texture similarity were determined. It was found that a combination of wavelet shrinkage and rotation-invariant local binary pattern best predicted the observer response. The results show that the proposed stationarity test is able to provide relevant information for texture analysis. [ABSTRACT FROM AUTHOR]

For a suspected forgery that involves the falsification of a document or its contents, the investigator will primarily analyze the document's paper and ink in order to establish the authenticity of the subject under investigation. As a non-destructive and contactless technique, Hyperspectral Imaging (HSI) is gaining popularity in the field of forensic document analysis. HSI returns more information compared to conventional three channel imaging systems due to the vast number of narrowband images recorded across the electromagnetic spectrum. As a result, HSI can provide better classification results. In this publication, we present results of an approach known as the t-Distributed Stochastic Neighbor Embedding (t-SNE) algorithm, which we have applied to HSI paper data analysis. Even though t-SNE has been widely accepted as a method for dimensionality reduction and visualization of high dimensional data, its usefulness has not yet been evaluated for the classification of paper data. In this research, we present a hyperspectral dataset of paper samples, and evaluate the clustering quality of the proposed method both visually and quantitatively. The t-SNE algorithm shows exceptional discrimination power when compared to traditional PCA with k-means clustering, in both visual and quantitative evaluations.

Two typographical errors in [Appl. Opt.57, 1918 (2018)]APOPAI0003-693510.1364/AO.57.001918 are identified and have been corrected here.

We evaluate an image-based multiangle bidirectional reflectance distribution function measurement setup by comparing it to measurements from two commercially available goniospectrophotometers. The image-based setup uses an RGB camera to perform bidirectional measurements of the sample material. We use a conversion matrix to calculate luminance from the captured data. The matrix is calculated using camera spectral sensitivities that are measured with a monochromator. Radiance factor of the sample material is measured using a commercially available tabletop goniospectrophotometer and compared to measurements made using the image-based setup in the colorimetric domain. Our measurement setup is validated by comparing the measurements performed using a goniospectrophotometer. Uncertainty and error propagation is calculated and taken into account for validation. The sample material measured is wax-based ink printed on packaging paper substrate commonly used in the print and packaging industry. Results obtained show that the image-based setup can perform bidirectional reflectance measurements with a known uncertainty. The goniospectrophotometer measurements lie within the uncertainty of the measurements performed by the image-based measurement setup. The setup can be used to perform bidirectional reflectance measurements on samples with properties similar to the samples used in this paper.