JAJSGI1 November 2018 DLP4710
During a given period of time, the nominal landed duty cycle of a given pixel is determined by the image content being displayed by that pixel.
For example, in the simplest case, when displaying pure-white on a given pixel for a given time period, that pixel will experience very close to a 100/0 landed duty cycle during that time period. Likewise, when displaying pure-black, the pixel will experience very close to a 0/100 landed duty cycle.
Between the two extremes (ignoring for the moment color and any image processing that may be applied to an incoming image), the landed duty cycle tracks one-to-one with the gray scale value, as shown in Table 1.
|Grayscale Value||Nominal Landed Duty Cycle|
Accounting for color rendition (but still ignoring image processing) requires knowing both the color intensity (from 0% to 100%) for each constituent primary color (red, green, and/or blue) for the given pixel as well as the color cycle time for each primary color, where “color cycle time” is the total percentage of the frame time that a given primary must be displayed in order to achieve the desired white point.
During a given period of time, the landed duty cycle of a given pixel can be calculated as follows:
For example, assume that the red, green and blue color cycle times are 50%, 20%, and 30% respectively (in order to achieve the desired white point), then the Landed Duty Cycle for various combinations of red, green, blue color intensities would be as shown in Table 2.
|Red Cycle Percentage||Green Cycle Percentage||Blue Cycle Percentage|
|Red Scale Value||Green Scale Value||Blue Scale Value||Nominal Landed Duty Cycle|
The last factor to account for in estimating the Landed Duty Cycle is any applied image processing. Within the DLP Controller DLPC3439 or DLPC3479, the two functions which affect Landed Duty Cycle are Gamma and IntelliBright™.
Gamma is a power function of the form Output_Level = A × Input_LevelGamma, where A is a scaling factor that is typically set to 1.
In the DLPC3430/DLPC3435 controller, gamma is applied to the incoming image data on a pixel-by-pixel basis. A typical gamma factor is 2.2, which transforms the incoming data as shown in Figure 19.
From Figure 19, if the gray scale value of a given input pixel is 40% (before gamma is applied), then gray scale value will be 13% after gamma is applied. Therefore, it can be seen that since gamma has a direct impact displayed gray scale level of a pixel, it also has a direct impact on the landed duty cycle of a pixel.
The IntelliBright algorithms content adaptive illumination control (CAIC) and local area brightness boost (LABB) also apply transform functions on the gray scale level of each pixel.
But while amount of gamma applied to every pixel (of every frame) is constant (the exponent, gamma, is constant), CAIC and LABB are both adaptive functions that can apply a different amounts of either boost or compression to every pixel of every frame.
Consideration must also be given to any image processing which occurs before the DLPC3439 or DLPC3479 controller.