Content Adaptive Illumination control (CAIC) is part of the IntelliBright® suite of advanced image processing algorithms that adaptively enhances brightness and reduces power. In common real-world image content most pixels in the images are well below full scale for the for the R (red), G (green), and B (blue) digital channels input to the DLPC34xx. As a result of this, the average picture level (APL) for the overall image is also well below full scale, and the dynamic range for the collective set of pixel values is not fully used. CAIC takes advantage of the headroom between the source image APL and the top of the available dynamic range of the display system.

CAIC evaluates images on a frame-by-frame basis and derives three unique digital gains, one for each of the R, G, and B color channel. During image processing, CAIC applies each gain to all pixels in the associated color channel. The calculated gain is applied to all pixels in that channel so that the pixels as a group collectively shift upward and as close to full scale as possible. To prevent any image quality degradation, the gains are set at the point where just a few pixels in each color channel are clipped. The Source Pixels for a Color Channel and Pixels for a Color Channel After CAIC Processing figures below show an example of the application of CAIC for one color channel.

Above, Figure 7-10 shows the gain that is applied to a color processing channel inside the DLPC34xx. Additionally, CAIC adjusts the power for the R, G, and B LED by commanding different LED currents. For each color channel of an individual frame, CAIC intelligently determines the optimal combination of digital gain and LED power. The user configurable CAIC settings heavily influence the amount of digital gain that is applied to a color channel and the LED power for that color.

(1) With CAIC enabled, if red and blue LEDs require less than nominal power for a given input image, the red and blue LED power will reduce.

Figure 7-12 CAIC Power Reduction Mode (for Constant Brightness)

As CAIC applies a digital gain to each color channel and adjusts the power to each LED, CAIC ensures the resulting color balance in the final image matches the target color balance for the projector system. Thus, the effective displayed white point of images is held constant by CAIC from frame to frame.

CAIC can be used to increase the overall image brightness while holding the total power for all LEDs constant, or CAIC can be used to hold the overall image brightness constant while decreasing LED power. In summary, CAIC has two primary modes of operation:

• Power reduction mode holds overall image brightness constant while reducing LED power
• Enhanced brightness mode holds overall LED power constant while enhancing image brightness

In power reduction mode, since the R, G, and B channels can be gained up by CAIC inside the DLPC34xx, the LED power can be reduced for any color channel until the brightness of the color on the screen is unchanged. Thus, CAIC can achieve an overall LED power reduction while maintaining the same overall image brightness as if CAIC was not used. Figure 7-12 shows an example of LED power reduction by CAIC for an image where the red and blue LEDs can consume less power.

In enhanced brightness mode the R, G, and B channels can be gained up by CAIC with LED power generally being held constant. This results in an enhanced brightness with no power savings.

While there are two primary modes of operation described, the DLPC34xx actually operates within the extremes of pure power reduction mode and enhanced brightness mode. The user can configure which operating mode the DLPC34xx will more closely follow by adjusting the CAIC gain setting as described in the software programmer's guide.

In addition to the above functionality, CAIC also can be used as a tool with which FOFO (full-on full-off) contrast on a projection system can be improved. While operating in power reduction mode, the DLPC34xx reduces LED power as the intensity of the image content for each color channel decreases. This will result in the LEDs operating at nominal settings with full-on content (a white screen) and reducing power output until the dimmest possible content (a black screen) is reached. In this latter case, the LEDs will be operating at minimum power output capacity and thus producing the minimum possible amount of off-state light. This optimization provided by CAIC will thereby improve FOFO contrast ratio. The given contrast ratio will further increase as nominal LED current (full-on state) is increased.