Colour enhancement

Researchers at Philips have developed a technique of building LCDs with an enlarged colour gamut, better colour saturation and higher screen brightness.

The design of current LCD TV panels is a compromise between colour gamut (the range of different colours that can be displayed) and display brightness.

Narrow spectrum red, green and blue filters are required in the panel to achieve the widest possible colour gamut, but these limit the amount of light transmitted through the display and hence reduce picture brightness.

Broad-spectrum colour filters increase light transmission, but significantly limit the range of saturated colours that can be displayed.

Philips Spectrum Sequential LCD technology enlarges the colour gamut of LCD TVs without losing picture brightness, by replacing conventional LCD TV backlighting by two sets of spectrally adjusted fluorescent tubes.

The phosphor mix in each set of tubes is adjusted so that one set, in combination with the colour filters, produces deep-red, green and blue outputs, while the other produces yellow, cyan and deep-blue outputs.

The two sets of tubes are switched on and off so that each set illuminates alternate picture frames, the pixel data for each frame being adjusted to suit the corresponding backlight spectrum.

Displayed sequentially at a frame rate high enough to eliminate flicker and colour breakup, each of the two separate colour gamuts created extends the range of displayable colours into a different area of the colour space.

Temporal colour averaging in the human eye then takes the process even further, extending the perceived colour gamut into areas of the colour space that neither of the individual gamuts could cover alone.

As a result, viewers see around 30% more colours with better colour saturation and higher screen brightness.

Lamp spectra (top) and colour triangles (bottom) of the Philips Spectrum Sequential display. The use of two lamps with different colour spectra as backlight extends the range of colours an LCD can display compared to the current PAL standard of the European Broadcasting Union.