Exploiting the more valid colour representation capabilities of the multi-primary systems is only accomplishable if the input device providing the data to be displayed supports the acquisition of the proper colour information multi-spectrally. For entertaining purposes this seems wastage of dataflow. However, in colour industry where the correct reproduction is needed and, also, the simulation of phenomena based on spectral levels such that the harmony changes of coloured fabrics switching to another type of illuminant, it is a useful device. If, for instance, standard 8-bits-per-channel-input (as known as true colour) is made available along a particular so called gamut extension (assigning the colour set of the multi-primary display to the standard three-primary input) displayed colours may seem more vivid on a multi-primary display but this, in turn, would not mean more appropriate colour reproduction just the ability to exhibit a greater set of colours. (Customers, however, often tend to choose the display devices out of more choices appearing more vivid to them.)
In this chapter sub-pixel rendering of modern displays was addressed together with formulating design principles concerning the ability to the visually optimal display of information. Discussing the goals of multi-primary displays sub-pixel rendering was investigated for systems encapsulating more than three primaries to visualize colour information. Recent systems either use the classical three primaries in sub-pixel-rendering-optimized layouts or stick to the stripe arrangement, which proved to lack critical structural abilities. Two new hexagonal sub-pixel architectures optimized for multi-primary colour displays were introduced, according to the design principles. These new multi-primary pixel architectures help eliminate the colour fringe artefact, known as the colour fringe error. They are expected to yield the display of better visual quality than the previous three primary colour architectures, including the RGB-stripe. Based on the character rendering example given in Section 3, the 7-primary system seems a better choice, but only
concerning its congenial geometric properties. To draw the final conclusions the optimal number of primaries should also be involved, which is a key question from the colorimetric point of view.
A new image rendering method was also formulated for multi-primary sub-pixel architectures. An error function was defined enabling proper chromaticity reproduction and enhanced luminance resolution. Revealing the proper balance between optimizing the chromaticity error (Ecol) and optimizing luminance reproduction (Elum), in order to achieve optimum multi-primary sub-pixel image rendering, is an important question.
S UMMARY
Without going into deep philosophical argumentation it is an accepted cliché in common fields of our everyday life that the presence of the change is the only issue that is unvarying. The desire to describe and get acquainted with the cause of observed phenomena and to widen our knowledge is the engine of this continuous revolution. In 2003 the life span of the 100-year-old cathode-ray tube technology came to a phase of great consequence: ‘flat panel displays surpassed the CRT as the best selling display, with world wide sales of over US$30 billion’.87
Colorimetric aspects of the cathode-ray tube are well documented.52-54,88 The increased occurrence of the FPDs in the availability of the display technologies all over the world not only demands the investigation of such devices from the colorimetric point of view but also offers the possibility to exploit their specific features in colour related research. The number of fields these novel devices can be taken advantage of or be further explored is endless. The greater stratification of the information society89 in the aging societies90 of the First World addresses age related topics of the display devices used, regarding the age sensitivity of the human visual system.91,92 So as, to bridge the different expectations93 of the users of different age, the optimization of recent colour displays to the needs of the elderly is one possible field, to mention another beside the two fields discussed in the previous chapters.
In this work the extremes were investigated: the macro world (large field colour appearance) and the micro world (level of pixels) of FPDs were visited. In one hand, the human colour perception changes caused by the exceptionally large screen compared to the field of view of the standard colorimetric observer, and, on the other hand, the sub-pixel arrangements and alternate colour rendering methods of multi-primary displays were examined. The final conclusions are summarized as theses in the forthcoming.
T HESES
Based on the results of the previous chapters, the following theses are formulated.
1. Colour appearance of immersive self-luminous scenes
1.1. The extension of the CIE colorimetric observers found in literature to model the colour appearance of homogenous colour stimuli larger than 20° cannot be used for extremely large homogeneous colour stimuli (visual angle >100°). (Chapter I, Section 2.2) 1.2. The colour perception of the almost immersive homogeneous colour stimulus is predictable by defining the colorimetric properties of a visually matching equivalent colour in terms of the CIE 1976 (L* a* b*) colour space with the following equations:
* *
st imm = 100 + 0.63( -100)
L L
( )
* *
imm st st st
* * +
= -0.008 + 1.5 -0.03 1
a L a L
( )
* *
st
imm st st
* *
-= -0.005 + 1.3 -0.02 4
b L b L ,
where L*st, a*st, and b*st mean the colorimetric (measured) L*, a*, and b* coordinates of the test stimulus.
The equivalently perceived colour is the colour perception of the stimulus (L*imm, a*imm, b*imm) viewed under 2° visual field on a mid-grey background and white surround, of which chromaticities are not too different from that of average daylight, by an observer photopically adapted to this field. (Chapter I, Sections 3.2.1 and 4)
1.3. There is no significant difference between the colour perception of the large homogeneous colour stimulus (>100°) if observers are exposed to the large stimulus for different durations (2 s and 8 s). This means that the perceptual colour differences between the two dissimilar sizes cannot only be assigned barely to chromatic adaptation to the large homogeneous colour stimulus after the investigated durations. (Chapter I, Section 3.2)
2. Sub-pixel arrangements and colour rendering methods for multi-primary displays
2.1. The colour fringe error due to undersampling arising in sub-pixel rendering – especially in case of achromatic objects – can be decreased by reforming the pixel structure of the common RGB-stripe dissolving the neighbouring sub-pixels of the same primary colour. By displaying graphical objects, the pixel structure of the new arrangements ensures a more uniform addition of the light output of the sub-pixels, hence decreasing the visual colour error, as proved by measurements. (Chapter II, Section 3)
2.2. Beyond a certain point decreasing surface area, the human visual system (HVS) is not able to perceive chromatic information but only luminous information. By using this property of the HVS, it is possible to define a colour image rendering algorithm for multi-primary displays that determines the intensity of the sub-pixels of the architecture such that the addition of their light output matches the expected colour of a certain location, while, within a pixel, the luminous intensity of the sub-pixel itself yields a higher resolution luminance information than the colour information. (Chapter II, Section 4)
T ÉZISEK
Az előző fejezetek eredményei a következő tézisekben kerülnek megfogalmazásra.
1. Teljes belemerüléssel vizsgált színingerek színmegjelenése
1.1. A Nemzetközi Világítástechnikai Bizottság (CIE) színingermérő észlelőinek az irodalomban található, 20°-nál nagyobb látószögű homogén színingerek színmegjelenését modellező kibővítései nem használhatók extrém nagy méretű homogén színingerek esetén (100° körüli látómező).
1.2. A majdnem teljes belemerüléssel vizsgált homogén színinger színészlelete előrejelezhető egy azzal azonos színészleletű ekvivalens színinger bevezetésével, mely színingermetrikai értékei a CIE 1976 L*a*b* színingermérő rendszerben az alábbi képletek alapján számíthatók:
* *
st imm = 100 + 0, 63( -100)
L L
( )
* *
st
imm st st
* * +
= -0, 008 + 1,5 -0, 03 1
a L a L
( )
* *
st
imm st st
* *
-= -0, 005 + 1,3 -0, 02 4
b L b L ,
ahol L*st, a*st és b*st a vizsgált színinger színingermetrikai (mért) L*, a* és b* értékeit jelenti.
Az ekvivalens színészlelet a 2°-os látószög alatt látszó (L*imm, a*imm, b*imm) koordinátákkal jellemezhető ekvivalens színinger, annak a természetes sugárzáseloszlás színességétől nem jelentősen eltérő színességű középszürke háttere és ennek fehér környezete által olyan szemlélőnél kiváltott színészlelet, aki e háttérhez és környezethez nappali fénysűrűségi szinten adaptálódott.
1.3. A belemerüléssel vizsgált színinger színészleletét a megfigyelési idő hossza (2 s és 8 s) nem befolyásolja szignifikánsan. Ez azt jelenti, hogy az eltérő méretű, azonos
színingerek észleletbéli különbsége nem tulajdonítható pusztán az ez alatt az idő alatt létrejövő, nagy homogén színingerhez való színi adaptáció eredményének.
2. Többcsatornás képmegjelenítők alpixel-elrendezései és színalkotási módozatai
2.1. Az alpixeles képalkotásnál az alulmintavételezésből eredő, különösen akromatikus alakzatok ábrázolásánál fellépő színes rojtozódási hiba a hagyományos RGB-elrendezésnél előforduló azonos alapszíningerek szomszédosságának megbontásával csökkenthető. Mérések igazolták, hogy a grafikus objektumok megjelenítésénél a bemutatott új architektúrák elősegítik az alpixelek által emittált fény egyenletesebb keveredését, így csökkentve a színes rojtozódási hibát.
2.2. A felületek csökkenésével az emberi látórendszer egy bizonyos küszöbérték után már nem képes színi információ befogadására, kizárólag intenzitást érzékel. Ezt a tulajdonságot kihasználva megadható olyan színalkotó eljárás többcsatornás képmegjelenítőkre, mely úgy határozza meg az alpixelek intenzitásértékeit, hogy azok egyéni fénykibocsátásának összege egy adott területen megfeleljen a megjelenítendő színingernek, míg egy képponton belül az alpixelek egyéni intenzitásértéke a színi információnál nagyobb felbontásban megadott fénysűrűség-információt közelítse.
A CKNOWLEDGEMENTS
Many people have contributed to this thesis. First and foremost I would like to thank my supervisors Dr. Peter Bodrogi and Prof. Dr. János Schanda for their work and support during my research. I am deeply grateful for their helpful comments from the beginning regarding any topics related to colour.
I have furthermore to thank the referees, Prof. dr. Ildikó Endrédy and Dr. Michael R.
Pointer, their valuable work and constructive critics reviewing the dissertation.
I would also like to thank the contribution and the committed discussions of my former fellow research colleagues Mr. László Beke, Mr. Peter Csuti, Dr. Balázs Kránicz and Dr.
Géza Várady and the kind work of my fellow graduating students Ms. Katalin Gócza and Ms. Enikő Troják during the years of research.
Finally, I would like to thank the smile of Zita, the support and understanding of my family and those who already live only in my memories.
R
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