Abstract

Color characteristics of an RGBW (red, green, blue, white) electrophoretic display (EPD) prototype developed by Samsung Electronics are analyzed. EPD shows strong crosstalk between subpixels because of both the fringe field between subpixels and the scattering phenomena at the display surface. An RGB-to-RGBW color-decomposition algorithm optimized to EPD characteristics is developed that compensates for color deterioration due to the fringe field and scattering phenomena. For the four-color-decomposition algorithm, white is added to the primary colors to enhance the reflectance of the vivid colors while minimizing chroma loss. The psychophysical experimental result shows that images rendered with the algorithms developed in this study are preferred more than 90% of the time over those rendered with algorithms from previous studies. This research proves that, in spite of the limited physical property of EPD, the color quality can be improved dramatically through the use of well-designed color-rendering algorithms.

© 2008 Optical Society of America

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Figures (15)

Fig. 1
Fig. 1

Cross section of EPD.

Fig. 2
Fig. 2

Four-color structured color filter array (Left: RGBW, Right: RGB3W).

Fig. 3
Fig. 3

45 / 0 color measurement geometry using a ring light source.

Fig. 4
Fig. 4

Spectral reflectance factor for the primary colors. (a) RGBW, (b) RGB3W.

Fig. 5
Fig. 5

Color gamut shown in CIE x y diagram ( 2 ° observer, D65).

Fig. 6
Fig. 6

Color gamuts in CIELAB color space (Solid: RGBW, Wireframe: RGB3W, Line: sRGB).

Fig. 7
Fig. 7

Crosstalk between subpixels.

Fig. 8
Fig. 8

Crosstalk test patterns for the RGBW panel.

Fig. 9
Fig. 9

Crosstalk test patterns for the RGB3W panel.

Fig. 10
Fig. 10

Crosstalk due to (a) fringe fields and (b) scattered lights.

Fig. 11
Fig. 11

Lee et al.’s RGB-to-RGBW decomposition algorithm shown in 2 D (Fig. 4 in [7]).

Fig. 12
Fig. 12

RGB-to-RGBW decomposition algorithm for EPD.

Fig. 13
Fig. 13

W out and R G B out functions for the four-color-decomposition algorithm.

Fig. 14
Fig. 14

Images used for the algorithm performance test.

Fig. 15
Fig. 15

Algorithm performance test results (z score).

Tables (5)

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Table 1 Radiance Reflectance of the Primary Colors

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Table 2 Measured Tristimulus Values of the RGBW and RGB3W Panels ( 2 ° Observer, D65)

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Table 3 Degree of Crosstalk for the RGBW EPD Panel

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Table 4 Degree of Crosstalk for the RGB3W EPD Panel

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Table 5 Performance Test Results for the Four-Color-Decomposition Algorithm

Equations (3)

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V = MAX ,
S = { 0 , if     MAX = 0 MAX MIN MAX , otherwise ,
H = { undefined if     MAX = MIN 60 G B MAX MIN + 0 if     MAX = R and G B 60 G B MAX MIN + 360 if     MAX = R and G < B 60 B R MAX MIN + 120 if     MAX = G 60 R G M A X - M I N + 240 if     MAX = B .

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