Simulating a CRT TV with C++ and OpenGL

http://nicktasios.nl/posts/simulating-a-crt-tv-with-c++-and-opengl.html

by ingve • 4 years ago

68 51 4 years ago

dtx12• 4 years ago

Quite interesting. The hardest part would probably not be the simulation but actually displaying what is simulated (in real time). You would need pretty high peak brightness and an insane refresh rate.

jeroenhd2• 4 years ago

I think modern (HDR with loads of nits of brightness, 144+ fps) gaming monitors should be able to get the effect down quite well. Nothing you'll find in a productivity oriented laptop but with the right tools you should be able to come quite close.

dtx12• 4 years ago

The peak brightness is there but not in per pixel dimmable displays (OLEDs) and you would need well above 15000 Hz to simulate a CRT.

mrandish• 4 years ago

Wow, I consider myself a pretty obsessive retro-gaming enthusiast (a custom-built arcade with 25-inch multi-scanning CRT, hacked graphics card and hand-tweaked GroovyMAME build) but damn, physically simulating a cathode ray tube is next level. Respect.

simonblack• 4 years ago

but damn, physically simulating a cathode ray tube is next level. Respect.

Definitely. While I have simulated monitor screens that were originally physical CRTs, I still simulated them as though they were digital monitors with defined pixels.

Definitely respect.

VikingCoder• 4 years ago

If you enjoy this look, I recommend checking this out:

https://github.com/Swordfish90/cool-retro-term

3234• 4 years ago

Has author actually seen a CRT TV image in real life?

Because it didn't look like that, you didn't have those clear distinct lines.

Color CRT displaying a game, no lines: https://i.imgur.com/eI2yb7Y.jpeg

Black & white CRT, you can barely make out the lines: https://d23gn3985hkc32.cloudfront.net/wp-content/uploads/202...

Asooka2• 4 years ago

Some CRTs do have visible scanlines, some do not. Check out this thread https://shmups.system11.org/viewtopic.php?f=6&t=63197 . Personally I'd like the simulated CRT to have no scanlines, rather what I want is temporal ghosting (previous frame blending in the next one, used for transparency effects in games by blinking two images rapidly); and a filter to make pixels less blocky and implement colour bleed. Given the great number of CRTs out there you probably can't have a single one be the best ever, but perhaps emulating several known ones by twiddling the parameters of the shader and letting people pick would be the best.

jeroenhd2• 4 years ago

When I look at CRT emulation, I always feel like I'm going crazy. It's been years since I last saw a CRT image but I don't remember visible scanlines at all.

I know the retro space is often specifically emulating old hardware, was thing a thing in the 80s, perhaps? Or were visible scanlines more common in America than in Europe? I know the weird colours and lowered resolution of some (emulated) games are an artifact of differences in NTSC/PAL/etc., could that explain the difference?

rikroots• 4 years ago

I think I understood your requirements, so I tried to knock up a 2d canvas filter demo[1] which met them. Sadly I don't think I met them, but I did end up creating a crazy weird motion blur effect (that's new to me) so thank you for helping me to accidentally create it!

[1] https://codepen.io/kaliedarik/pen/OJZzJJB ... warning: demo requests access to the device camera.

bjt2n3904• 4 years ago

Yeah -- it seems that so many of the CRT simulations way overemphasize the scan lines. I think if they added a bit of "bloom" to each pixel, it would make them less obvious?

jeffbee2• 4 years ago

They over-emphasize the negative space between the scan lines without getting the details of the raster scan correct. The forward scan lines are not horizontal, they are slightly tilted, because the vertical sweep is continuous. The retrace is also slightly slanted, but less because the retrace is faster. So in the diagram on this site the solid lines should be the ones that slope, and the dashed retrace lines should be the ones that are nearly horizontal.

an1sotropy• 4 years ago

Another way to think about the horizontal scanlines is that within the lines, there is really a continuous analog signal, undergoing various (analog) filters along the way from initial detection up through final display, but between scanlines there is discrete sampling. This can be emulated by digital filters, but even if the final display doesn't show the scanlines, there should be a different point-spread-function in the horizontal versus the vertical direction.

There's also the possibility of emulating how the time resolution could be less than the refresh rate (sometimes sluggish phosphors create a kind of motion blur).

Really old tv transmissions also had an effects like a high-pass filtering (I think to show better detail within limited dynamic range)[1], and how really bright spots would be surrounded by dark halos [2]. The distinctive "look" of old TV has a lot to do not just with the CRT display, but the characteristics of the analog method of video signal generation, in a video camera tube [3] that had its own cathode raw sweeping across the source image.

[1] look at the edges of the desk at around 0:36 in https://www.newsweek.com/wmttv-black-white-color-first-time-...

[2] https://movies.stackexchange.com/questions/113358/whats-with...

[3] https://en.wikipedia.org/wiki/Video_camera_tube

werdnapk• 4 years ago

I recall as a kid, getting right up close to the screen and looking at the picture on the TV and noticing the lines. Further away from the TV, then yes, the lines were not visible.

mras03• 4 years ago

Guess it depends. I haven't had a CRT TV for many years, but I have an old multisync CRT monitor and I can clearly see the individual raster lines (close up of 320x200 progressive scan: https://i.imgur.com/Osc4ZMm.jpeg). At normal viewing distances it's not noticeable though.

dm319• 4 years ago

Deluxe Paint, ah! fond memories!

smusamashah• 4 years ago

At normal viewing distances

Yes thats what it was all about. The pixelated game graphics were made with that and other CRT properties in mind.

hulitu4• 4 years ago

multisync CRT monitor
320x200

21" by chance ? Why would someone use 320x200 on a monitor when only the very old DOS games need such a mode ?

MarkusWandel2• 4 years ago

It would make sense to adjust the "line width" (focus!) of the scanlines so they blur into each other. But on a multisync monitor, this would be matched to the highest resolution it can display. Without fancy defocusing circuitry, of course if you display only 200 scanlines on a monitor capable of 5x as many, you're going to get a lot of black space between them. This bothered me personally, in those days, in my case with a 20" CRT monitor and emulation of my old C64 environment. Modern "CRT emulation" is better than the real thing, in this case.

naikrovek2• 4 years ago

I had a consumer CRT as a child (the family TV in the living room) whose scanlines were apparent even at 6ft away, and it was only a 19" screen.

maybe my eyes were better than most, I don't know, but I distinctly remember trying to adjust the settings so the lines would go away, thus reducing the annoyance of my "all I can see is colored lines" brother.

hulitu4• 4 years ago

It seems that he didn't. And he also does not understand how a cathodic tube works (i.e. persistence).

SyneRyder• 4 years ago

Color CRT displaying a game, no lines: https://i.imgur.com/eI2yb7Y.jpeg

Try loading the 4000x3000 version of that image you linked and zooming to full size. Especially on the green character's outfit, you can see the scanlines on that color CRT display.

3234• 4 years ago

If you put your eyeball to the screen, sure, just like you can see the pixels of an LCD screen. But it's not how you're supposed to look at it.

ogurechny3• 4 years ago

Along with different properties of the beam other comments mention, there was also a question of dot pitch, i. e. properties of the phosphor grid. Also, the circuits generating the signals in consumer hardware often did not have that much of the full bandwidth, or the most correct wave forms.

kevin_thibedeau• 4 years ago

That is a late 90s television with a small tube. You can most definitely see the scanlines on old arcade CRTs. The shadowmask on a color CRT enhances the lines so comparison to B&W isn't meaningful.

wormik• 4 years ago

Imho electron gun alignment topic - see https://www.javatpoint.com/computer-graphics-color-crt-monit...

jeffbee2• 4 years ago

These seem to regularly pop up on HN but the new ones never seem to describe the ways in which they differ from the now-20-years-old xanalogtv hack.

71a54xd• 4 years ago

Does anyone have experience doing this purely with FFMPEG?

naikrovek2• 4 years ago

yes the int10h font guy has some blog posts about it, with accompanying code on GitHub.

https://int10h.org/blog/

atum47• 4 years ago

I did a project a few weeks ago where I was trying to emulate CRT images as well. End up creating a CRT converter for still images.

https://victorribeiro.com/CRT/

I guess each one of us remember CRT a little bit differently, since my images end up with vertical stripes instead of horizontal ones.

MarkusWandel2• 4 years ago

This may not be perfectly realistic, but it's getting close and can be made closer. Not long ago, replacing a dead 26" colour CRT (say, in an arcade game machine) with a suitably masked 4K LCD panel would have been ludicrous. But we're pretty much there now.

I thought when incandescent bulbs pretty much went away that I would miss the bare filament in a clear bulb look. I kind of do, but not much. I have a chandelier with the fake-filament LED type bulbs in it. Despite dubious cooling of the LEDs they seem to be holding up just fine in extended use, and while it doesn't look quite traditional, it's good enough.

And emulation of older video game systems has moved into the browser!

ncmncm• 4 years ago

I was hoping it would distort the image to round the corners and compress the edges.

Extra credit for added snow.

some-guy• 4 years ago

I used a CRT for the first time in a long time a few months ago (embedded in a PowerMac 7200 all-in-one), and I forgot how stunning the picture looked compared to LCD/LED screens throughout the 2000s.

Big problem though, I forgot how much they made my eyes _hurt_. I couldn't handle using it for more than 30 minutes. Increasing the refresh rate to 75hz helped a little bit, but wasn't enough to get me to stop causing a headache. I'm all for nostalgia but I think in the end it is good that we moved away from CRT technology (for many reasons).

anthk• 4 years ago

NFSU2 on CRT looked glorious and vibrant. On LCD's it's pretty much bland and faded off.

Simulating a CRT TV with C++ and OpenGL

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