How does Television work?

[ppppenguin]

The first type of CCD mentioned by Refugee is a frame transfer CCD: https://en.wikipedia.org/wiki/Charge-cou...ansfer_CCD They gave good results in early broadcast grade CCD cameras. Rather like film, they expose the whole frame at one go, to be read later sequentially as required. This is very different to tube cameras where each part of the picture is read at a different time.

Notes about CCD and CMOS image sensors:
https://en.wikipedia.org/wiki/Charge-coupled_device
https://en.wikipedia.org/wiki/Active-pixel_sensor

What I'm not sure of is where analogue to digital conversion is done on modern sensors. The actual sensing is still analogue so there must be an ADC somwhere. Or more than one.

PS: This article suggests that multiple on-chip ADCs are common for high performance: https://possibility.teledyneimaging.com/...om-a-to-d/

[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.

[jjl]

Steve

You asked the same question in 2014 on the VRAT forum here. Some of the same people as on this thread provided answers.

John

[Panrock]

Whoops... always a little embarrassing when that happens. And proof of the patience of the good people on both forums.

I suppose this shows I am (still) finding the answers difficult to conceptualise in a memorable form. Maybe this is because 'television' is no longer a separate discipline but rather just another part of multi-faceted computer technology. Sorry if this sounds pompous.

Steve

[jjl]

Steve

I agree that modern television systems could be perceived as "applied computing". The availability of large amounts memory at low cost, high performance microprocessors and complex ASICs has transformed television from a complex analogue system to, in many ways a relatively simpler, largely digital system.

John

[Mike Watterson]

I wrote an article in 1986 about how broadcasting, communications systems in general and computing had originated and would converge. Oddly some things I wrote about did happen and then essentially died. Most current TV broadcasting networks assume fixed TVs and most locations need a fixed outdoor aerial. Pocket colour TVs were a short lived market and phones with a built in broadcast TV receiver even more short lived (DVB-t and DVB-h). Many phones and tablets only have an FM radio because the function is built into the WiFi & Bluetooth chip. Phones with no earphone socket have it disabled. Tablets that could have built in VHF aerial only work with the headset as the aerial. I've used an €10 DVB-T USB stick on a phone and a tablet (Android has drivers and app on the PlayStore) and the issue is signal strength even though our local TV multiplex TX is about 13 km away. Same with using the radio stations on DVB-t (DAB was turned off last May, only had RTE and best bit rate was 128K MP2 with about 43% coverage). The stick can be used as an SDR from 42 MHz to 1.4 GHz (any mode including DRM and DAB, people sell 100 kHz to 30 MHz upconverters too). A USB2Go adaptor is needed.

[Mike Watterson]

TV is now very complex with more standards than the Analogue era even without  including cable, satellite and streaming/IP modes. But most of the insides of a TV are the PSU, backlight controller, and screen driving. The input interfaces isn't much and the tuner (complete receiver) is almost nothing. The real terms cost price of a 46" 4K HDR TV is less than decent mains radio set before FM in the UK. The late 1950s motorised tuning SABA AM/FM sets were a terrific price.

It looks very simple, physically.

Screens are so cheap I recently bought two 24" 2 K monitors (2560 x 1440) with stands for landscape or portrait. The first ones that I've bought that are better than the old Dell 19" CRTs for photo-editing. The pair together were less than 1/2 the price of a decent laptop. I have 2x €45 Satellite receivers via a €10 four way HDMI switch on the one fed from the laptop. The dish system just above the shed roof gets 28.2E, 23.5E (only 3 inputs), 19.2E, 13E and 9E (Ka Band, one polarity/band) into a multi-switch to feed up to 12 satellite tuners. One feed is to a TV in the living room and another to satbox there so that people can swap between a German channel and a UK one without channel changing, just input select. The demo and shopping 4K channels on 13E and 19.2E only work on the sat tuners built into the 4K TV. The cheap €45 boxes don't have RTE or BBC MHEG5, but you can tune the "red button" channels direct and use the USB HDD recording.

The recording on HDD is now very simple as a TV or setbox simply records the transport stream after demultiplexing from the other channels but before decompression. Thus replay is identical quality to live and is simpler than analogue video recording either on analogue media, DVD-R or HDD. I actually use a 2.5" drive out of a scrapped laptop in a €8 SATA-USB adaptor case. You don't need what are called AV HDDs as the TV or Setbox has ample RAM to buffer any time the drive decides to recalibrate.