Theoretical Prediction of Colours and Illuminants in sRGB Colour Space

Photometric parameters and the evaluation of colour phenomena based on real human perception of light and colour were introduced into colour science in the first half of the 20th century. However, in the last two decades some known software programs for 3D computer graphics attempt to simulate realistic light source and optical effects with the help of photometric parameters. The reason for somewhat late arrival of such software applications can be found in the prevalent use of RGB colour space and the complexity of achieving realistic light source and colour effects. The aim of the research was to write and implement a simple gamut compression algorithm that will make colour transformation from input XYZ data to appropriate RGB data of sRGB colour space within large number of colours (1872) and different illuminants (16), and also to define appropriate light source intensity in 3D modelling software to achieve optimal matching of simulated and real photographic lights with predefined RGB values. Due to discrepancies between real light sources and the interpretation of light source colours in 3D, RGB colours of sRGB had to be adjusted with calibration procedure developed. The results of the research offer the possibility for theoretical prediction of virtual colours and light source intensity for different colours of light sources

Theory of Colour Harmony and Its Application

The colour represents an essential element of visual and graphic communications. It plays an important role in the perception of visual design and it is significant for all participants in the process of planning, developing and promoting graphic products. Designers are interested in a psychological and presentational aspect of colours, while to the technologists the colour represents one of the most important quality attributes. The process of choosing colours that are harmonious, usable and efficient is complex. In addition, many designers have inadequate background knowledge of colour theory, which could help them with the selection of colours. As a result, designers usually spend a great deal of time and expend significant effort in choosing appropriate colour combinations. In this article, the importance of colour harmony and its application when extracting colours, rating and generating colour schemes is presented

Comparision of Two Thermal Decomposition Offset Printing Plates

The aim of our research was to investigate two digital plates based on the same type of thermal sensitive coating produced by different manufactures and compare their quality, run length, ecological and economical aspects and user experience in the offset press. It was found out that with both plates the same quality of prints was attained according to the measurements of tone values on the plates and prints. The spectrophotometric measurements also showed that the prints were almost identical, except for minor differences in lightness. The microscopic image analysis showed that one plate had finer graining and thereby gave better and more accurate representation of half-tone dot and this plate was also more environmentally–friendly with lower consumption of chemicals for the plate developing, more durable with longer run lengths and as well more economical and user–friendly. The obtained results were useful for the offset printing company in its choosing the better thermal plate with reduced production costs

Colorimetric Accuracy of Color Reproductions in the 3D Scenes

Color is a complex phenomenon that depends on the object, the observer and the light source, while the color reproduction additionally includes the surrounding conditions and it depends on the device that can either capture, display or print the reproduction. Colour accuracy is very important for digital reproduction of artistic work where colour represents essence of art. In our research, color reproductions of renderings of computer generated scenes, including an object, background and lights were assessed, and even more, colorimetric accuracy in renderings was analyzed. With assumption that shading in 3D computer generated scenes plays an important role in visual perception of rendered color, the colors were analyzed on renderings of shaded objects. It was determined that colorimetric accuracy depends on the position on rendered objects, either illuminated or shaded. Furthermore, it was discovered that color lightness and hue, light intensity and background influenced ΔRGB values

Study of Camera Spectral Reflectance Reconstruction Performance using CPU and GPU Artificial Neural Network Modelling

Reconstruction of reflectance spectra from camera RGB values is possible, if characteristics of the illumination source, optics and sensors are known. If not, additional information about these has to be somehow acquired. If alongside with pictures taken, RGB values of some colour patches with known reflectance spectra are obtained under the same illumination conditions, the reflectance reconstruction models can be created based on artificial neural networks (ANN). In Matlab, multilayer feedforward networks can be trained using different algorithms. In our study we hypothesized that the scaled conjugate gradient back propagation (BP) algorithm when executed on Graphics Processing Unit, is very fast, but in terms of convergence and performance, it does not match Levenberg-Marquardt algorithm (LM), which, on the other hand, executes only on CPU and is therefore much more time-consuming. We also presumed that there exists a correlation between the two algorithms and is manifested through a dependency of MSE to the number of hidden layer neurons, and therefore the faster BP algorithm could be used to narrow the search span with the LM algorithm to find the best ANN for reflectance reconstruction. The conducted experiment confirmed speed superiority of the BP algorithm but also confirmed better convergence and accuracy of reflectance reconstruction with the LM algorithm. The correlation of reflectance recovery results with ANNs modelled by both training algorithms was confirmed, and a strong correlation was found between the 3rd order polynomial approximation of the LM and BP algorithm\u27s test performances for both mean and best performance

Rendering Techniques in 3D Computer Graphics Based on Changes in the Brightness of the Object Background

Maintaining accurate colour constancy and constant colour appearance are only a few challenges one must conquer in a modern day digital three‐dimensional (3D) production. Many different factors influence the reproduction of colour in 3D rendering and one of the most important is certainly rendering engines. In our research, we have studied rendering of colours with three rendering engines (Blender Render, Cycles and Yafaray) of an open source 3D creation suite based on changes in the brightness of the object background from 20 to 80%. In one of these cases, colour of the object was adapted to the lighter background using the colour appearance model CIECAM02. With the analysis of colour differences, lightness and chroma between colours rendered using different rendering engines; we found out that rendering engines differently interpret colour, although the RGB values of colours and scene parameters were the same. Differences were particularly evident when rendering engine Cycles was used. However, Cycles also takes into account the object background. Numerical results of such research provide findings, which relate to the respective environment, and also these certainly demonstrate the successful implementation of the colour appearance model CIECAM02 in the 3D technologies and, in our opinion to other software packages for 3D computer graphics

Theoretical Prediction of Colours and Illuminants in sRGB Colour Space

Photometric parameters and the evaluation of colour phenomena based on real human perception of light and colour were introduced into colour science in the first half of the 20th century. However, in the last two decades some known software programs for 3D computer graphics attempt to simulate realistic light source and optical effects with the help of photometric parameters. The reason for somewhat late arrival of such software applications can be found in the prevalent use of RGB colour space and the complexity of achieving realistic light source and colour effects. The aim of the research was to write and implement a simple gamut compression algorithm that will make colour transformation from input XYZ data to appropriate RGB data of sRGB colour space within large number of colours (1872) and different illuminants (16), and also to define appropriate light source intensity in 3D modelling software to achieve optimal matching of simulated and real photographic lights with predefined RGB values. Due to discrepancies between real light sources and the interpretation of light source colours in 3D, RGB colours of sRGB had to be adjusted with calibration procedure developed. The results of the research offer the possibility for theoretical prediction of virtual colours and light source intensity for different colours of light sources

Analysis of color profile quality of digital projector

The aim of the present study was to analyze the display of colors in digital projection. For this purpose the digital projector NEC NP210 was used. The measurements were performed in accordance with the instructions and recommendations of ISO standards. Our goal was to research the creation of color profile of the projector using a EyeOne Pro spectrophotometer and to establish whether the size of color gamut of standardized sRGB color space can be reached by characterization of the digital projector modules. By using the color chart Color Checker Classic, the photometric and colorimetric accuracy of the characterized and uncharacterized projection were evaluated. In the final part of the research, comparison between the colorimetric accuracy of the computer screen and the digital projector was performed. The results showed that by module characterization of the NEC NP210 Movie projector in studio conditions, the same size of the color space could not be achieved as by using the default sRGB module. Evaluation of colorimetric accuracy by using the digitalized color chart Color Checker Classic provides usable results, especially when the display of chromatic colors with emphasis on skin tones, and achromatic colors with emphasis on grey balance or chromaticity respectively, were examined. Based on the obtained results of the computer screen and digital projector comparison, it could be concluded that both compared computer screens match the standards. Overall, the NEC NP210 projector with the sRGB default module without profile could be also used if necessary. Thus, we can sum up that digital projection displaying standardized sRGB color space could not be comparable to a high quality CRT or LCD computer screen

Performance Of Five Chromatic Adaptation Transforms Using Large Number Of Color Patches

Input devices in general use light sources with different color temperatures. As a consequence, in color acquisition, display and rendering processes a number of chromatic adaptations transforms (cats) are being used. In our study, color transformations between three illuminant source pairs (d50-a, d50-d65 and d65-a) were investigated using five cats (Bradford, von Kries, xyz Scaling, cmccat97 and cmccat00). Research was made on 8190 color patches that were printed with inkjet printer. Results showed that color differences obtained with the Bradford method were the lowest regardless of the implemented illuminant source pair. The same ranking of cats was observed in all combination of illuminant source pairs, however the smallest color differences were generated with d50-d65 cats and the biggest with d65-a models

CIECAM02 and Perception of Colour in 3D Computer Generated Graphics

Kljub tehnološkemu napredku zadnjih stoletij in desetletij se še vedno soočamo s problematiko prikaza in upodobitve barve v različnih medijih in ohranjanja zaznave barve. Ena od možnosti, za katero se lahko odločimo pri zagotavljanju stalne barvne zaznave, so modeli barvnega zaznavanja. Trenutno je aktualen CIECAM02, ki se še vedno ne uporablja v 3D računalniški grafi ki, s katero se vsak dan srečujemo. Namen raziskave je bil pregled barvnih prostorov v 3D računalniški grafiki, pregled reprodukcije barv in materialov, algoritmov za senčenje ter izbranih sodobnih tehnologij upodabljanja za doseganje korektne končne vizualizacije. V nadaljevanju smo želeli proučiti model barvnega zaznavanja CIECAM02 do te mere, da bi ga lahko uporabili v povezavi s 3D računalniško grafiko. V ta namen smo v programu Blender postavili testno sceno in jo upodobili s tremi upodobljevalniki: Blender Render in Cycles, ki sta že vgrajena, in z dodatkom Yafaray. Izkazalo se je, da CIECAM02 lahko uporabimo tudi v 3D prostoru in da z njegovo uporabo dobimo boljše rezultate ujemanja barv pri spremembi ozadja. Poleg tega smo ugotovili, da barv ne upodabljajo vsi upodobljevalniki enako. Omenjena raziskava je aktualna za vse, ki želijo svoje dvo- ali tridimezionalne izdelke predstaviti s pomočjo 3D računalniške grafike, torej tudi za področje vizualizacij oblačil in tekstilnih izdelkov, ki se uporabljajo pri modnem oblikovanju in oblikovanju interjerjev, avtomobilski, navtični in letalski industriji ter tudi širše, kjer so dovršene 3D vizualizacije tekstilij in oblačil nepogrešljivi element vizualnih in grafičnih komunikacij