Generating Greyscale

TDI™ employs a temporal method of rendering greyscale images. This involves switching each pixel rapidly between light and dark states at a specific rate such that, when integrated by the HVS, constant luminance at the required level is perceived. Figure 1 illustrates an 8 bit greyscale image for the RED subfield.  Each bit-plane, Most Significant Bit (MSB) to Least Significant Bit (LSB), is illuminated using a binary-weighted Pulse-Width Modulated (PWM) red light source. In other words, the 8-bit pixel value is split into eight 1-bit binary values that are ‘displayed’ (i.e. the pixel is turned ON or OFF) sequentially according to their weight in the corresponding illumination time slot.

Consequently, there are 24 1-bit bit-planes for a 8-bit R/G/B system, 8 bit-planes for each primary colour.  These bit-planes would drive each pixel according to the binary value of that pixel in the time slot associated for that bit-plane and colour.

This concept is further illustrated in Figure 2. This shows how the picture information is displayed within one frame for each colour subfield and with their respective bit-planes and how they relate to the binary weighted PWM illumination scheme.

Figure 1. Binary weighted bit-planes for an 8-bit colour subfield

Binary weighted bit-planes for an 8-bit colour subfield

Figure 2. Complete full colour TDI rendered frame

Complete full colour TDI rendered frame