Faroudja

What exactly is LED backlighting?

A LCD TV is made up of multiple layers to create an image.  For this discussion, we will focus on two main elements: the LED  backlight and the LCD panel.

The LED layer creates the light that passes through the LCD panel.  The LCD panel creates the color and shapes that we see.  The LCD panel also controls the amount of light that passes from the LED layer to the viewer's eyes.

When there is a dark scene in a movie, the LCD panel tries to block the light from the backlight.  However, some light will leak through.  To compensate, the LCD panel has to completely shut off the light. This gives a good contrast ratio rating (the differerence between dark and light areas) but does not allow the subtle details in the shadows to be seen.

LED-BLAC was created to help deal with this issue and improve the image.  On TVs with direct-lighted LED panels where the backlight is separated into sections, or zones, we can adjust the backlight to improve image quality.

Zones and grids

The backlight is physically divided into a number of horizontal and vertical zones, typically in a regular pattern, as seen below.

The brightness of each zone can be independently controlled.  Some systems use RGB LEDs, and some use white LEDs.

To make calculations simpler, zones are sub-divided into a number of virtual grids.

The solution is scalable for direct, edge or hybrid LED backlight designs.

An example of LED backlighting in a high-contrast scene

In the scene-capture at left, advanced LED TV technology is used to create an image of an old lightbulb in a dark room.  The interest here is seeing how the LED TV deals with  the transition from full white in the center to full black on the edges.

The bottom image is of the LED backlighting for this movie scene.  The LED-BLAC technology manipulates the different zones based on the image.

• The black areas of the image get blacker since there is less light to leak through to the front of the LCD panel.
• The contrast ratio increases; in the bright regions the backlighting is fully on, whereas in the dark regions, the backlighting is significantly reduced.
• Because some of the LEDs are on very low, an added benefit is a sizeable reduction in power consumption, ensuring that the TV meets energy rating requirements.

Again, looking at the image of the backlighting, you can see the zones that are at different light levels.  Also, these zones are square in shape and don't exactly line up with the image on the screen.

The light from one zone will always "spill" over into the next zone.  This light decay from zone to zone is consistent and can be accurately measured, as shown in the model of zone decay shown below.

A powerful and flexible programming tool that interfaces with a high-resolution CCD camera analyzes this decay, and creates look-up tables to store the data.  The inverse of this decay is applied to the TV panel to ensure that the image is correct, without halos or flickering.  The data is calculated on a per-pixel basis for accuracy.

The LED-BLAC technology is also useful for the unique processing required for 3D TV.

The next layer of processing is applying the Faroudja Video Optimized calibration technology for very accurate color, detail and shadow processing.