I was researching in psychophysic on optic experiment and I stumble upon my laptop manufacturer'screen specs. There is a 60hz refresh rate with exponentially decaying lums intensity between each tick. Wouldn't it be visually nicer if the digital video signal were converted to continuous analogical first and then feed each led continuously as it happen in audio transducer ?
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It's just not feasible. In a full HD display panel, there are 1920 x 1080 x 3 = 6,220,800 pixels. That would be over 6 million wires to connect each one to a drive circuit. And 6 million pins on the panel. And 6 million drivers. It's really not possible to build. So what they do instead is multiplex - row and colum wires with a pixel at each crossing. This brings down the number of wires required to 1920 x 3 + 1080 = 6,840. That's much more reasonable. This nicely maps to the video signal, which arrives one line at a time.
Generally the way the pixels are built on an LCD screen is there is a transistor patterned onto the glass for each pixel, and then each pixel looks like a capacitor. The screen ends up looking like a write-only DRAM. The capacitance of the pixels will hold the level between updates. In an LED display, each pixel also has an LED which will discharge the capacitor between frames, leading to the flickering. A good solution might be just to double the frame rate so that the flickering is at a higher frequency and therefore less noticeable.
answered Oct 13, 2014 at 8:27
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\$\begingroup\$ The number of wire might not be the problem as we can imagine led directly mounted on a pcb whose production is now fully automated. By hand I would understand, but Socs, microprocessors and ICs in general have shown that imagination appears to be the limit of what can be manufactured. From what you described it look like the problem would come from the number of DAC necessary to feed millions of led simultaneously (as many as the number of leds), when a line of dac (1080 in your example) is sufficuent to feed all of the leds in serial? \$\endgroup\$– user9020Commented Oct 13, 2014 at 8:58
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\$\begingroup\$ @user9020 the number of wires is definitely a problem as 1- we're not talking about chip-level but actual wires, that can be up to 1m long or more, and 2- 6 million LED drivers is an insane amount for a screen. You can't see more than 24 Hz anyway. \$\endgroup\$ Commented Oct 13, 2014 at 9:37
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\$\begingroup\$ @clabacchio Thank! But beside my question 24Hz seams like a tolerance threshold to me. Some recents finding show some optical nerve cells functioning as photons counter... In the cognitive stage, nerve data is integrated over time and then interpreted so this might smooth things but I'm almost certain that difference limens goes far beyond 24hz. \$\endgroup\$– user9020Commented Oct 13, 2014 at 9:59
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\$\begingroup\$ xcorr.net/2011/11/20/… 24fps is near the threshold for moving images, but there is a clear perception difference between 24fps and 48 or 60 fps. 75Hz is closer to the threshold for flicker (dark frame). \$\endgroup\$ Commented Oct 13, 2014 at 14:33
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\$\begingroup\$ @mskfisher thanks for the link. But commentaries at the end seams to take over my point. \$\endgroup\$– user9020Commented Oct 14, 2014 at 18:35