Evaluation of the perceived colour difference under different lighting for museum applications

The role of lighting in museums has a fundamental importance. Light influences the perception of colours and space in the collections on display, therefore, any type of lighting must be adequately analysed to confirm the suitability and undistorted colour rendering of the illuminated objects. A two-stage perceptual test was carried out for this purpose. Initially, the participants were asked to evaluate the illuminants according to criteria such as: the brilliance of the colours, the degree of pleasantness of the lighting and the degree of overall satisfaction of the setting. Subsequently, the efficiency of different illuminants for the identification of colour differences between two objects was tested. The results obtained were then compared with the most commonly used colour rendering and colour difference indicators in order to determine their potential and limits

Fundamentals of color teaching in post-graduate education

In this research we present a framework on the theory of color culture and science education in the context of a master program in Color De sign & Technology organized in Italy since 2014. Th e master is organize d in three main phases Fundamentals, Project Work and Internship. The first phase is composed of lectures and theoretical lessons that gives the students a base from theory and technique, relating to disciplines such as physics, optics, colorimetry, psych ology and perception . Fundamentals give all the base knowledge that the students are then asked to integrate in the project works, to propose and develop color projects for different design assignments , and in the Internship, that establish a link between the academia and compan ies who work with color in various fields like design, architecture, textiles and paints. Here the F undamentals will allow the students to build up their future professional experience in the chosen field

Spatial–Spectral Evidence of Glare Influence on Hyperspectral Acquisitions

Glare is an unwanted optical phenomenon which affects imaging systems with optics. This paper presents for the first time a set of hyperspectral image (HSI) acquisitions and measurements to verify how glare affects acquired HSI data in standard conditions. We acquired two ColorCheckers (CCs) in three different lighting conditions, with different backgrounds, different exposure times, and different orientations. The reflectance spectra obtained from the imaging system have been compared to pointwise reference measures obtained with contact spectrophotometers. To assess and identify the influence of glare, we present the Glare Effect (GE) index, which compares the contrast of the grayscale patches of the CC in the hyperspectral images with the contrast of the reference spectra of the same patches. We evaluate, in both spatial and spectral domains, the amount of glare affecting every hyperspectral image in each acquisition scenario, clearly evidencing an unwanted light contribution to the reflectance spectra of each point, which increases especially for darker pixels and pixels close to light sources or bright patche

Computational methods of restoration quality assessment

Image quality assessments are part of the quality of experience measures and are a hot topic in image enhancement and image processing techniques. Image quality metrics are useful for the evaluation of the error introduced by a specific process, or the enhancement of an algorithm. Image luminance, contrast, colour distribution, smoothness, presence of noise or of geometric distortions are some examples of low level cues usually contributing to image quality. Aesthetic canons and trends, displacement of the objects in the scene, significance and message of the imaged visual content are instances of the high level (i.e. semantic) concepts that may be involved in image quality assessment To this aim, low-level IQ metrics aim to compute difference from a reference and a distorted image, but high-level metrics must include in their computation a model of Human Visual System (HVS). In this context, different metrics try to simulate some behaviour of the HVS and try to give a definition of quality based on some specific vision features, but until today no one metric can include all the complexities of the vision. An application of particular interest for image quality is film restoration where filo-logical constraints and lack of reference aim are a difficult challenge for automatic evaluation. However, the world of film restoration is subject to a fast-technical growth that makes the application of image quality metrics mandatory. Aiming to provide a overview of the existing image quality metrics assessments, in our work we want to analyse the limits and the challenges of the use of different image quality metrics on restored film frames. In this presentation we describe the main methods used in film restoration to assess the quality of a frame/film enhancement and the most used methods to quantify the quality of an image. Different results will be reported, and the first solutions of our research will be presented

Designing a Cockpit for Image Quality Evaluation

Image Quality (IQ) as assessed by humans is a concept hard to be defined, since it relies on many different features, including both low level and high level visual characteristics. Image luminance, contrast, color distribution, smoothness, presence of noise or of geometric distortions are some examples of low level cues usually contributing to image quality. Aesthetic canons and trends, displacement of the objects in the scene, significance and message of the imaged visual content are instances of the high level (i.e. semantic) concepts that may be involved in image quality assessment. Despite subjective evaluation of IQ being very popular in many applications (e.g. image restoration, colorization and noise removal), it may be scarcely reliable due to subjectivity issues and biases. Therefore, an objective evaluation, i.e. an image quality assessment based on visual features extracted from the image and mathematically modelled, is highly desirable, since it guarantees the repeatability of the results and it enables the automation of image quality measurements. Here the crucial point lies in the detection of visual elements salient for IQ. Many objective, numerical measures have been proposed in the literature. They differ from one another in the features considered to be relevant to IQ, and in the presence of a reference image, an image of \u201cperfect\u201d quality with which to compare the image to be evaluated. Objective measures are thus broadly classified as full-reference, reduced-reference or no-reference, according to the availability of reference information. Due to the complexity of the IQ assessment process, a single measure may be not robust and accurate enough to capture and numerically summarize all the aspects concurring to IQ. Therefore, we propose to employ multiple objective IQ measures assembled in a cockpit of objective IQ measures. This cockpit should be designed to offer not only an extensive analysis and overview of features relevant to IQ, but also as a tool to automate the selection of machine vision algorithms devoted to image enhancement. In this work we describe a preliminary version of a cockpit, and we employ it to assess a set of images of the same scene acquired under different conditions, with different devices or even processed by computer algorithms

Algorithms for film digital restoration: unsupervised approaches for film frames enhancement

Since the beginning of this Century we are assisting to a crucial step in the domain of cinema: the transition from analogic to digital. The computed generated imagery substituted the early developed special effects on film and the use of smartphones and digital devices took the place of old Super8 formats. In this context, film restoration passes quite often by the digitization and the use of software for image enhancement and restoration are widely diffused and used also by non-pro users. The digital restoration of colour has widely spread, and digital techniques allow to easier removal of colour casts, frames histograms equalization, dynamic range expansion and saturation adjustment. Despite this easy applicability, when adjusting the colour of a film of historical value, constant supervision by qualified personnel is still required. In our contribution we show and resume our results from the works and projects we have conducted in digital film restoration and we describe our method based on the idea of recovering the original appearance of colours instead of the original colour signal. This approach is based on the application of Spatial Colour Algorithms (SCAs), a family of algorithms inspired by the capabilities of Human Visual System (HSV) of autonomously adjust the variation of lightness and colours in a scene. SCAs are based on the idea that colour sensation does not depend on the pointwise value of the stimulus, but on the spatial arrangement of the stimuli in the scene. In fact, identical levels of radiance at a point can originate completely different colour sensations according to the values in the rest of the image. To reproduce this behaviour SCAs performs spatial comparisons among the pixels in the input image and for this reason SCAs are characterized by a high computational cost and a local and global behaviour. All the SCAs present a common structure: a first step in which each pixel is recomputed according to the spatial distribution of the other pixels in the image, in the second step an adjustment can be added according to the SCA goal. Due to this characteristic, SCAs can be suitable for analog-to-digital dynamic range adjustment or colour enhancement when the fading occurred on a film. Thanks to the SCAs algorithms is possible to conduct a semi-automatic and unsupervised colour restoration on faded frames, with a technique that permit also to non-pro users to operate on film restoration without the need of expensive and complex software. This solution could be an interesting alternative to classical restoration approach in the domain of little archives or institution that aim to valorise and diffuse their collections and records without the need of a complex and long process of restoration. In addition those new methods could open an interesting discussion in how evaluate the quality of a restored film, and how to proceed in a restoration when there are no references

A cockpit of multiple measures for assessing film restoration quality

In machine vision, the idea of expressing the quality of a films by a single value is very popular. Usually this value is computed by processing a set of image features with the aim of resembling as much as pos- sible a kind of human judgment of the film quality. Since human quality assessment is a complex mech- anism involving many different perceptual aspects, we believe that such approach may scarcely provide a comprehensive analysis. Especially in the field of digital movie restoration, a single score can hardly provide reliable information about the effects of the various restoring operations. For this reason we in- troduce an alternative approach, where a set of measures, describing over time basic global and local visual properties of the film frames, is computed in an unsupervised way and delivered to expert evalu- ators for checking the restoration pipeline and results. The proposed framework can be viewed as a car or airplane cockpit , whose parameters (i.e. the computed measures) are necessary to control the machine status and performance. This cockpit, which is publicly available online, would like to support the digital restoration process and its assessment

I colori di “Toute une nuit” : analisi e confronto tra metodi di restauro manuali e automatici

Toute une Nuit \ue8 un film franco-belga del 1982 scritto e diretto dalla regista francese Chantal Akerman. Attraverso il leitmotiv di \u201cL\u2019amore perdoner\ue0\u201d di Gino Lorenzi, la regista mostra gli intrecci romantici di vari personaggi nel corso di tutta una notte, sullo sfondo di una cupa e silenziosa citt\ue0 belga. Il formato offertoci dalla Cinematek (Cinematheque Royale de Belgique) presentava evidenti discrepanze rispetto a quello che doveva essere il film in origine, motivo per cui abbiamo svolto delle sperimentazioni attraverso l\u2019utilizzo di due differenti software ai fini di rendere il film il meno divergente possibile rispetto all\u2019originale. In primis il film \ue8 stato suddiviso in sequenze, dopodich\ue9 le pi\uf9 significative sono state scelte per l\u2019estrazione dei key frames: frame significativi a cui applicare i software. Il primo software utilizzato \ue8 ACE (Automatic Color Equalization) ed \ue8 appunto un algoritmo di equalizzazione cromatica automatica in grado di simulare alcuni meccanismi del HVS (Human Visual System), con particolare attenzione per la color constancy e per la lightness constancy. Il secondo software utilizzato su Toute Une Nuit \ue8 Da Vinci Resolve, un programma di editing audio-video manuale. Di questo secondo programma in particolare \ue8 stato utilizzato principalmente la sezione (page of functionality) Color la quale dispone di tutti i controlli per la manipolazione del colore e del contrasto, la riduzione del rumore e la realizzazione di molti altri aggiustamenti correttivi e stilistici. La valutazione dei risultati \ue8 stata effettuata tramite il confronto dei key frames. Il primo confronto, pi\uf9 evidente, \ue8 stato possibile attraverso il confronto visivo dei key frames cui sono stati applicati i due differenti algoritmi. Un secondo confronto, pi\uf9 analitico, \ue8 stato invece possibile per mezzo degli istogrammi delle immagini, in particolare sono stati realizzati gli istogrammi per ciascun canale R, G, B e per la luminanza di ogni key frame

The influence of Spatial arrangement of a scene in the stability of color appearance under different lights

Color rendering is defined as the \u201ceffect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant\u201d[1]. A Color Rendering Index (CRI) aims to indicate through one or more values the range of the color variation of an object after changes in the illumination of the scene. In other words, it tries to quantify to what extent the chromatic appearance of an object is preserved under a given light source with reference to a standard illuminant. Goal of a CRI is to evaluate the quality of a light source given that a \u201cgood\u201d illuminant should keep color appearance as much unchanged as possible. With the arrival of novel LED based light sources, classic CRI proved not to be a measure in line with the human visual color sensation. As a follow up, a series of new methods and algorithms to compute alternative CRIs have been devised and tested, but no one has emerged as the definitive one. This paper aims at suggesting a potential weakness of all CRIs,: they get as input just the spectral power distribution (SPD) of the light source and implement a Color Adaptation Transform (CAT) as a simplification of the Human Vision System (HVS), ignoring its spatial mechanisms. In everyday life, perceptive characteristics of objects are strongly dependent on the context in which they are placed since we rarely see colors in isolation, as well as on the quality and SPD of light radiation[2]. Classic examples in which the spatial distribution of a scene plays an important role in the color appearance are the optical illusions. We aim to study if the spatial arrangement of a scene may influence the final appearance under different illuminants[3,4] and thus if it should consider it in its computation

All the colours of a film: study of the chromatic variation of movies

In this work, we discuss and present different techniques for film colour summarization together with a preliminary colorimetric study. The aim of this project is to combine the frames of different videos, reducing them to just one image of chromatic significance. This elaboration is made through two different methods: the movie barcodes and long exposure images. Due to their nature, those concise images have not only an artistical aim, but are movies chromatic synthesis that can eventually be used for colour checks and for identification of dominances. At first, we applied those methods on two videos from the Pixar Animation Studios\u2019 short animation movies. Then, as preliminary test, we present an application on the frames of a homemade video altered in different ways together with the relative visual and numerical results