Upravljanje digitalnom slikom s Color Checker kontrolnim stripom

Petar Miljković1, Dean Valdec1, Diana Bratić2

petar.miljkovic@unin.hr
1 Sveučilište Sjever, Trg dr. Žarka Dolinara 1, Koprivnica, Hrvatska
2 Sveučilište u Zagrebu Grafički fakultet, Getaldićeva 2, Zagreb, Hrvatska

Sažetak

U ovom radu prikazana je provedba Color Management procesa gdje je proveden proces kalibracije (ugađanja) uređaja koji se koristi u reprodukcijskom procesu s poznatim (referentnim) vrijednostima na mjernom stripu. U digitalnim sustavima reprodukcije, upravljanje prostorima obojenja kontrolirano je transformacijom vrijednosti unutar različitih prostora s graničnim vrijednostima gamuta. Vizualnom percepcijom informacija o slici osiguran je široki spektar boja koji je podložan korekciji prema Color Checker kontrolnom stripu. Percepcija boja uzrokovana je različitim stimulusom (podražajem) a ovisi o izvoru svjetla, nelinearnom odzivu senzora i spektralnim karakteristikama filtra. Korekcijom prostora obojenja izrađuje se perceptualno uniformni pristup koji osigurava traženi gamut. Algoritmom za obradu digitalne slike, snimljene informacije korigirane se prema izlaznim dijagramima kromatičnosti gdje se upotrebom umjerenih profila prilagođavaju potrebama tiska ili web izdanja. Vizualna percepcija različitih krivulja obojenja u različitim uvjetima osvjetljenja (metamerija) nameće za potrebu klasifikaciju vrijednosti kako bijelog balansa tako i ostalih primarnih i sekundarnih boja. Osiguravaju se granične vrijednosti gamuta osvijetljena gdje referentni uvjeti upadnog svjetla utječu na reprodukciju digitalnog zapisa. Naknadnim kvantitativnim mjerenjem dviju vrijednosti obojenja na originalu i kontrolnom stripu ispunjeni su preduvjeti za analizu i naknadnu korekciju istih.
Ključne riječi: Color Checker, Color Management, digitalna slika, gamut, metamerija.

Management of Digital Image with Color Checker Control Strip

Abstract

This paper presents the realization of the Color Management process which implemented the calibration process (tuning) of the device used in the reproduction process with the known (reference) values on the measuring strip. In digital reproduction systems, the management of the coloured areas is controlled by the transformation of values within different areas with the limited values of gamut. The visual perception of the image information provides a wide range of colours, which is subject to the correction in accordance with the Color Checker control strip.The perception of colours is caused by a different stimuli and depends on the light source, the non-linear response of the sensor and the spectral characteristics of the filter. The correction of the coloured areas provides a perceptually uniform approach that ensures the required gamut. The algorithm for processing of digital images enables the correction of the recorded information according to the output chromaticity diagrams, where the use of moderate profiles is adapted to the needs of print or Web editions.The visual perception of different colouring curves in different lighting conditions (metamerism) imposes the need for classification of values as a white balance and other primary and secondary colours. Thus, the limit values of gamut of illumination are secured, where the reference conditions of the input light affect the reproduction of the digital content. The subsequent quantitative measurement of two values on colouring, on the original strip and the control strip, creates the preconditions for their analysis and their further correction.
Keywords: Color Checker, Color Management, digital image, gamut, metamerism.


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