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How does a screen work?

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572 points chkhd | 1 comments | 13 Jul 25 14:09 UTC | HN request time: 0.205s | source
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perching_aix ◴[13 Jul 25 23:46 UTC] No.44554866[source]▶
There are some sentences in this that are technically vague enough to pass, but I don't think are strictly speaking correct, and I believe will likely lead to a mistaken understanding:

> modern displays don't paint the image line-by-line (...) They light up each pixel simultaneously, refreshing the entire display at once.

The entire screen area is lit all the time now, yes, but refresh still typically happens line by line, top to bottom [0], left to right [0], for both LCDs and OLEDs. It's a scanning refresh, not a global refresh (sadly).

You can experimentally confirm this using a typical smartphone. Assuming a 60 Hz screen refresh, recording in slow motion will give you enough extra frames that the smartphone camera also likely operating in a scanning fashion (rolling shutter) won't impact the experiment. On the recording, you should see your screen refreshing in the aforementioned fashion.

[0] actual refresh direction depends on the display, this is for a typical desktop monitor

replies(4): >>44555043 #>>44555165 #>>44556616 #>>44556858 #
1. bitwize ◴[14 Jul 25 00:31 UTC] No.44555165[source]▶
Indeed, one feature of active-matrix (and even passive-matrix) displays is that it needs only m + n signal lines to address a pixel in an m + n display. To change the color of a pixel, a signal goes out over the lines corresponding to the row and column of the addressed pixel, selecting it; and then another signal is transmitted over another line to actually change the value of that pixel. In this scheme, it would be impossible to address all pixels simultaneously. Nor would you actually want to, as this would require millions of control lines to drive the display!