Gloss, as has long been known, is a far more complex visual concept than the present methods of instrumental gloss evaluation are able to characterize. The instrumental analyses are either highly over-simplified (standard gloss meters) or over-simplified but with results still difficult to interpret (goniophotometry). The dimensionality and power of the directed reflectance information measured by existing tools is lower and less expressive than the information gained from a direct visual examination of a surface. The purpose of this paper is to review important gloss measurement issues, in the context of perceptual evaluation. This work gives a background for defining necessary requirements for an evaluation system that can reveal the perceptually relevant gloss features of the surface measured.

Gloss, as has long been known, is a far more complex visual concept than the present methods of instrumental gloss evaluation are able to characterize. The instrumental analyses are either highly oversimplified (standard gloss meters) or oversimplified but with results still difficult to interpret (goniophotometry). The dimensionality and power of the directed reflectance information measured by existing tools is lower and less expressive than the information gained from a direct visual examination of a surface. In this article, a new measurement principle for gloss characterization is presented, aimed to give more comprehensive gloss information, which at the same time has an intuitive interpretation. The integrated optical system is compact and has illumination and receptor devices in fixed positions, which facilitates a mechanically simple realization. The instrument is a goniophotometer with a spatial resolution, but it is restricted to a constant angle between the illumination and the receptor. The measurement yields a "ReflectanceVectorMap" (RVM) which is an approximate optical equivalent to the surface measured. The RVM simultaneously contains spatially resolved information about directed reflectance and surface apparent inclination. The resolution is high in both spatial and in angular coordinates. The measurement provides a complex massive data set, which when appropriately visualized is similar to the visual properties of the original surface and thus encourages further evaluation and interpretation. A homogeneity index called "GlossAngleSmoothness" (GAS) is introduced, derived from the RVM, by weighing perceptually "positive" and "negative" components of gloss. The index correlates well with results obtained by a panel of experienced gloss judges asked to rate gloss homogeneity for the limited but demanding set of black printed paper surfaces tested. The GAS index performs considerably better than a panel of inexperienced judges.

Gloss, as has long been known, is a visual concept far more complex than the present methods of instrumental gloss evaluation are able to characterize. A newly developed measurement principle for gloss characterization gives perceptually relevant gloss information. The characterization results in a Reflectance Vector Map (RVM) which simultaneously contains spatially resolved information about directed reflectance and apparent inclination. The experimental phase of the present study uses the RVM and a rudimentary model of a virtual optical environment to interactively visualize a simulated surface. The performance of the visualization environment has been evaluated by comparing results from two visual assessments of perceived gloss homogeneity for a limited but demanding set of black printed paper surfaces. Assessments were performed both on the physical surfaces, and on the computer generated visualizations of the same surfaces, reconstructed from the corresponding RVM’s. The results correlate well, with a less inter-judge variance in the visualization environment than with the physical surfaces. It is suggested that this visualization environment may be a powerful tool for gloss assessment, able to mediate perceptually important characteristics of gloss.

Sensor interpixel correlation (IC), as caused by crosstalk, interpixel capacitance, the brighter–fatter effect, blooming or smear, lowers the sensor MTF and increases color distortion in color filter array sensors. This is generally overlooked, and challenging to mitigate. Recent findings regarding scientific grade (CCD or hybrid CMOS) sensors, describe non-linearities causing pixel charge accumulation dependent IC. This is relevant even for lower grade sensors. High dynamic range imaging (HDRI) is especially susceptible to IC, because the sensor is deliberately operated partly in saturation. Existing HDRI algorithms exclude saturated pixels but generally overlook IC. This review article motivates the need for a generalization of the point spread function (PSF) into an irradiance-exposure dependent (IED) PSF, also considering supersaturation. The IED PSF is challenging to characterize and apply, partly due to its non-linearity. However, doing so can improve the MTF irrespective of image sensor technology, and for conventional as well as HDRI imaging.

High dynamic range imaging (HDRI) by bracketing of low dynamic range (LDR) images is demanding, as the sensor is deliberately operated at saturation. This exacerbates any crosstalk, interpixel capacitance, blooming and smear, all causing interpixel correlations (IC) and a deteriorated modulation transfer function (MTF). Established HDRI algorithms exclude saturated pixels, but generally overlook IC. This work presents a calibration method to estimate the affected region from saturated pixels for a color filter array (CFA) sensor, using the native CFA as a matched filter. The method minimizes color crosstalk given a set of candidates for proximity regions, and requires no special setup. Results are shown for a 21-bit HDR output image with improved color fidelity and reduced noise. The calibration reduces IC in the LDR images and is performed only once for a given sensor. The improvement is applicable to any HDRI algorithm based on CFA image bracketing, irrespective of sensor technology. Generalizations to subsaturated and supersaturated pixels are described, facilitating a suggested irradiance-exposure dependent point spread function charge repatriation strategy.

Detailed optical characterization of the relevant features of optically variable devices (OVD) is in general a challenge. Adding to the in general high both spatial and angular resolved characteristics, the high dynamic range of reflection, including high intensity specular reflections and low intensity reflections of other geometries make the metrology even more demanding. A trichromatic reflectance measurement service recently made commercially available, addresses the stated challenges. The resulting data may be described as a spatially resolved trichromatic goniophotometric characterization. The massive data set generated may be approached either by developed visualization tools (static images and dynamic videos) or processed mathematically into higher-order characterizations. The number of potential relevant applications is abundant – one example may be a detailed angular characterization of the iridescent color shifts; how the iridescence function is distorted due to the topography of the underlying paper. The application is demanding in part because the analysis involves spatial and angular dimensions over a high dynamic range of reflectance (specular and non-specular). Besides the OVD, there are other optical document security functions that are challenging to characterize in detail, and where this novel service may prove a useful tool for the professionals in the business.

GonioLabs’ DOVID Reader (GDR) provides a spatially resolved trichromatic goniophotometric characterization. The present work discusses how the GDR quantifies optical features and differences between them (defects), as appreciated by perceptual evaluation. GDR advantages are a) evaluating different DOVID suppliers, b) gaining more detailed understanding of deterioration due to circulation, c) forensic evaluation of different groups of counterfeits potentially originating from the same production equipment

The advent of digital printing stresses the importance of quality measurement. Print quality measures that give an objective value have long been sought. The aim is 10 be able to dcscrihe objectively the properties of print on paper so that conclusions regarding the apparent quality can be drawn. In this paper, we discuss the measures proposed in the literature and relate them to the subjective quality. Several years ago, the concept of ‘information capacity’ was proposed as such a measure. Some reflections are made in the light of coding. and telecommunication theory. areas in which in information capacity is a vital tool. On the other hand. for the print quality applications. the interest in in formation capacity has in fact been decreasing. An obvious question therefore arises and is treated in this work: Why have we seen so few applications of this theory for practical applications in the area of print? Is the area of print quality so very different from the areas or image compression and telecommunication?