How does Television work?

[Mike Watterson]

Actually all viable real time motion cameras expose the entire frame and separately read it in some sort of serial fashion (which might be 32 bits parallel per pixel) to the next stage of processing. Some specialised cameras are one line that's mechanically imaged, but not real time motion video. Farnsworth's camera was a failure because unlike EMI/RCA it only sensed the light as the analogue pixel was read, rather than an exposure time of the entire frame. Basically chip cameras replace the scanning electron beam reading a mosaic with an IC and have used various types of photo-sensitive semiconductors, as did the tube cameras. Colour is then either using three chips, or filter stripes or a filter pattern. The photo sensitive elements might not be square/rectangular, might not exactly fit a raster (ie. hex or pentile) and for single chip cameras there can be 3 to 6 sensors or sub-pixels for each logical pixel. The Luminance signal is interpolated from separate pixels data in a single chip camera. A three chip camera is simpler as Luminance is (x x R) + (y x G) + (z x B) where x, y & z depend on the losses of the splitter and the sensitivity at those wavelengths. A Bayer pattern single chip needs more complex interpolation than even a stripe filter simply using three adjacent pixels in the line for RGB. Then the two chrominance signals are calculated. This is all done in an ASIC version of an FPGA prototype that used DSP as the sensor signals are converted to digital on the chip. The processing chip may interpolate frames and use a larger image than the output image so as to remove movement jitter. It may have DSP for reducing noise when the light level is low. Some sensors can run at a much lower frame rate in low light to increase sensitivity with the processing chip interpolating to the the desired 24, 25, 30, 48, 50, 60 or higher frame rates. Some consumer camera systems can record at high frame rates in bright light to achieve "slowed motion" at normal playback for sport.