[FPD International] CMO: Backlight Reproduces Vivid Colors w/ 2 Types of RGB LEDs

Oct 30, 2007
Motoaki Itou, Nikkei Electronics
The LCD panel based on MultiPrimary technology, capable of displaying vivid colors
The LCD panel based on MultiPrimary technology, capable of displaying vivid colors
[Click to enlarge image]

Chi Mei Optoelectronics Corp (CMO) of Taiwan developed a backlight technology to reproduce vivid colors with the combined use of two sets of RGB LED light sources.

The two sets of light sources have properties different from each other in the chromaticity diagram. The company exhibited an LCD panel based on this technology at FPD International 2007.

The technology, called MultiPrimary, provides an effect equivalent to that achieved by increasing the number of color filters, while eliminating the problems resulting from the provision of additional filters.

MultiPrimary technology uses two sets of RGB LED light sources. One of them is a standard light source used in LED backlights, which covers 88% of the NTSC color gamut. The other is an RGB LED light source that uses LEDs with G and B color properties in the chromaticity diagram that are different from those of the LEDs used in the first set.

The latter set covers 65% of the NTSC color gamut, complementing the color space corresponding to cyan, as the first set only has a small representation area of cyan. The total gamut of the both sets reaches 102% NTSC. Meanwhile, the properties of R color light sources in both sets are identical.

Filters for three colors, namely R, G and B, are used in the technology. In order to reproduce vivid colors, there is another technique that uses five filters, ie, Y (yellow) and C (cyan) filters in addition to those for RGB.

But the use of five filters causes problems such as the reduction of aperture ratio and resolution and the increase of production processes. The latest technology is free from such problems because it only uses three color filters as with the existing technology.

According to MultiPrimary technology, image data at 120 Hz is displayed by alternately turning on the two sets of light sources. When the first set is turned on, the panel is driven to display image data obtained by eliminating the color corresponding to cyan from the normal image data.

When the second set is turned on, the panel is driven to display image data of cyan alone. The OCB display mode, which has a shorter gray-level response time, is employed as the panel display method.

Considering the purpose of the second set, the R light source seems unnecessary. If the color space corresponding to Y or M (magenta) must be complemented in the future, the company may employ an R light source with properties different from that of its counterpart used in the first set.

The MultiPrimary display method
The MultiPrimary display method
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The chromaticity diagrams of the two sets of light sources used in MultiPrimary technology
The chromaticity diagrams of the two sets of light sources used in MultiPrimary technology
[Click to enlarge image]