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How does a screen work?

makingsoftware.com

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Re: How does a screen work?

#81

Post by perching_aix »

krackers wrote: post #80
perching_aix wrote: post #64

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…

Assuming a 60Hz refresh rate, does it take ~16ms (± the vblank inteval) for a complete cycle from top-left to bottom-right? Or does the scan happen faster than that (with something else being the limiting factor on overall refresh rate)?

Yes, the refresh cycle takes ~16.6 ms. There's another "point" chasing behind the refresh "point", that will be where the panel's response time has finished catching up with the refresh. In between these points, the pixels are slowly morphing from one color to the next. On LCDs, the area between these two points is quite sizeable, definitely more than a few lines, sometimes even hundreds of lines. On a 1080p 60 Hz display, just 1 ms of response time corresponds to 64.8 lines (6% of the screen) being constantly in flux, for example.

The difference between LCDs and CRTs in this regard then, is that on a CRT you only ever got light during that chase section. The initial state is full darkness, and the final state is full darkness too. It's a pulse.

Re: How does a screen work?

#82

Post by rocqua »

I'm much more interested in the hardware driver. This thing gets digital encoded input, has to decode it, and then multiplex it to 8 million pixels. 60 times a second. Being able to hit at least 4 million different levels (talking about 4K 60fps 12 bit color).

The input is roughly serial, so it takes a massive serial to parallel conversion.

Re: How does a screen work?

#83

Post by Aardwolf »

rocqua wrote: post #82

I'm much more interested in the hardware driver. This thing gets digital encoded input, has to decode it, and then multiplex it to 8 million pixels. 60 times a second. Being able to hit at least 4 million different levels (talking about 4K 60fps 12 bit color). The input is roughly serial, so it takes a massive serial to parallel conversion.

Yeah, with an electron beam it's clear that it's a continuous signal and a single beam is being controlled, but how do you drive millions of individual digital pixels all at once, how does the signal get routed correctly to each one if them?

Re: How does a screen work?

#84

Post by kfarber »

qwertox wrote: post #3

Not only was the initial diagram all/explaining, but the "pop"-"pip" on zoom-unzoom of the image was just as nice as playing with a sheet of bubble wrap. Wow, and that ruler on the right side, even with the sound. One of the nicest pages I have been on. And the landing page... https://www.makingsoftware.com/ It just keeps on giving.

Agreed, absolutely stunning diagrams and visual design.

Re: How does a screen work?

#85

Post by nedt »

Sharlin wrote: post #31

CRT displays are one of those analog technologies that are arguably much cooler than their digital successors. Think – a literan raygun, a particle accelerator, inside your monitor, creating the image you're looking at.

It's much cooler if you haven't used it. That mass of a 19in was crazy. Then you had all of those that had the high pitched noise. And if you were unlucky you had to degauss them. Cool concept, but in practice the digital successors are better.

Re: How does a screen work?

#86

Post by nedt »

If the author is here.

Would be nice if you could give a hint on all the disabled chapters. Either a tooltip or even just a title attribute. Are they paid? Do I have to login? Not ready yet?

Re: How does a screen work?

#87

Post by p_l »

Aardwolf wrote: post #83
rocqua wrote: post #82

I'm much more interested in the hardware driver. This thing gets digital encoded input, has to decode it, and then multiplex it to 8 million pixels. 60 times a second. Being able to hit at least 4 million different levels (talking about 4K 60fps 12 bit color). The input is roughly serial, so it takes a massive serial to parallel conversion.

Yeah, with an electron beam it's clear that it's a continuous signal and a single beam is being controlled, but how do you drive millions of individual digital pixels all at once, how does the signal get routed correctly to each one if them?

with older HDMI/DVI displays, AFAIK you sync pixel clock to "address generator" for the matrix, with major issue becoming scaler AFAIK.

DVI (and thus older HDMI) being essentially "VGA that skipped Digital to Analog conversion" you're riding the beam, including porches.

Re: How does a screen work?

#89

Post by taneq »

kurthr wrote: post #66
perching_aix wrote: post #64

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…

I was glad they at least mentioned how IPS (PLS) and VA differ from older TN. But you're right both LCD and OLED refresh a stored voltage on the cell (or caps) on a roughly line by line (OLED can easily be 5 clocks on the GIP to cancel internal transistor offset voltages). I was mostly annoyed that they didn't mention the circular polarizer on OLEDs. Although there is discussion of going to color filters with Quantum…

Maybe slightly off topic but I was surprised to discover that my glasses with photoreactive lenses (SpecSavers ‘Reactions’) are actually circularly polarised but only when they go dark. I originally thought they didn’t work because they didn’t interact with another pair of polarised sunglasses (no changing brightness as I rotated one lens in front of the other) but later noticed that my phone screen with its circularly polarised IPS screen was almost black in bright sunlight… until I took my glasses off.

Re: How does a screen work?

#90

Post by cubefox »

bgnn wrote: post #52
layer8 wrote: post #38

Earlier quoted context omitted.

The phosphor still drops off very quickly [0][1][2], roughly within a millisecond. That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity. On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest. The slow-motion recording showing roughly one line at a time therefore seems accu…

I'm not sure about this calculation though. Phosphor decays exponentially with a time constant of roughly 5ms (according to HP [1]). This means when a new frame comes at 60Hz refresh rate there is still 10-15% of the previous frame related excitation is present. This means there is considerable amount of nonlinearity, hence the performance is even worse than 10ms LCD/OLED displays. Genuine question: why do you think…

> Genuine question: why do you think CRTs are better?

They have many disadvantages, but an advantage is that CRTs mostly remove the "persistence blur" induced by smooth pursuit eye movements on sample-and-hold displays like LCD and OLED. Here is an explanation:

https://news.ycombinator.com/item?id=42604613

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