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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]

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]

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]