footprint electronics is working on a new type of LCD control concept.

The goal is to achieve a high-resolution, high-contrast and color-intensive LCD. A distinction is made between three variants below:

1. LCD Standard

2. LCD Standard High-resolution

3. LCD RGB-Image-dependent (footprint electronics)

LCD Standard

LCD-Standard use static white light as backlight (BL) to display images. To display 3-color images, RGB-colorfilter are required, which mix a color from the gamut of the backlight.

LCD Standard High-resolution

Another variant of displaying 3-color images on an LCD is to use RGB light as the backlight. With this LCD-control, the colormixing is due to the sequential control of the individual primary RGB-colors of the backlight in combination with the control of the colorless pixels. The result is a high-resolution LCD, since no colorfilter are used.

Comparison of both variants:

Nr.	LCD Standard	LCD Standard High-resolution
1	static BL	dynamic BL
2	BL consisting of a one-color light source (white)	BL consisting of a three-color light source (Red-Green-Blue)
3	three colorfilter (Red-Green-Blue)	no colorfilter
4	no sequential LCD-control	sequential LCD-control

	BL off: black	BL off: black

Both LCD-variants have in common that the Xy-color space of the backlight is constant. A constant Xy-color space of the backlight has a negative effect on the image quality in dark images. The aim of the image-dependent LCD-variant is to generate dark images in good quality. This LCD-variant generates a variable Xy-color space of backlight, which can be controlled image-dependent.

LCD RGB-Image-dependent

Based on the high-resolution LCD-variant, a variable Xy-color space of backlight is generated. This is achieved in three sequential steps by lighting up all three primary RGB-colors at the same time.

The ON-time of the RGB-primary colors is individually controlled by using pulse-width-modulation (PWM). Any Xy-chromaticity coordinate from the entire color space of the three primary colors (gamut) can be mixed.

Three mixed colors (M1,M2,M3) result in three sequential steps, which span a reduced and image-dependent color-triangle.

Figure 1 shows a PWM-control and a resulting color space (M1,M2,M3) from the gamut (R,G,B).

Figure 2 shows the color space of an RGB-LED that spans the color-triangle (R,G,B) and a reduced color-triangle (R',G',B') in the gamut (R,G,B).

Figure 3 shows the colors of the backlight from the three sequential steps of a LCD-control.

Natural images use only a subset of the gamut. In this case only a reduced color-triangle (R',G',B') is required. With the pixel-data of the LCD-pixels, each color from the color-triangle (R',G',B') can be mixed.

Features LCD RGB-Image-dependent:

1. Shorter ON-time of the backlight

2. Higher contrast ratio

3. Low energy consumption

Another advantage of this backlight is that in addition to RGB-LED, RGB-OLED is also possible as backlight.

PWM-control	color space (M1,M2,M3)

Mixed color M1 Mixed color M2 Mixed color M3
Figure 1

color space RGB-LED (R,G,B)	color space image (R',G',B')

Figure 2


RGB-BL (black off)	R'G'B'-BL (black off)
Figure 3

Note: Exemplary color spaces

Panten application DPMA: 10 2017 004 500.3