CRT emulation provides authentic retro gaming

Written by Ben Hardwidge

May 5, 2009 // 3:08 p.m.

Tags: #2600 #afterimage #atari #bogost #crt #emulation #georgia #ian #institute #noise #rf #scanlines #stella #technology #texture

While it’s easy enough to get emulation software for 8-bit computers and consoles, you’re never going to be able to relive the proper experience without a flimsy digital joystick and a CRT TV rather than a flashy LCD monitor. We’re not talking about the decent CRT technology found in last-generation TVs and monitors; we mean the Evil Edna-style box that you might have plugged into the RF socket of an Atari 2600 in 1982. However, researchers at the Georgia Institute of Technology reckon that they’ve managed to successfully emulate the quirks of a dodgy CRT on an LCD, in order to enable an authentic retro gaming experience.

Taking the Atari 2600 Stella emulator as their foundation, team of coders set about recreating the scanline patterns, ghosting effects and colour-bleed that the crustier gamers among us might remember from childhood Breakout sessions. Ian Bogost, who instigated the project, explains that “many of today's players may only experience Atari games in emulation. Indeed, many of my students may have little to no memory of CRT televisions at all. Given such factors, it seems even more important to improve the graphical accuracy of tools like Stella.”

Bogost says he gave a Tech Computer Science capstone group the task of modifying Stella to accurately simulate several effects associated with CRTs. These included noise from the RF signal, colour-bleed between scanlines and the edges of sprites, plus afterimage effects. Bogost describes the latter saying that it was the result of the phosphor glow, which he says “leaves more of an afterimage on the human retina compared to an LCD display. As a result, images might linger after they had moved or changed. Atari programmers took advantage of this feature to "flicker" objects between frames.”

As well as this, Bogost wanted Stella to emulate the “texture” of sprites seen on a CRT TV. He notes that “the display itself is not constructed out of pixels like a monitor, but out of the phosphorescent glow of an electron beam as it shines through a focusing grate. The result produces slightly separated coloured dots on the screen, which become less visible as the viewer moves away from the set.”

Anyone who regularly watches DVD movies on a CRT TV will know that compressed movies often appear to be much smoother and cleaner than they are on an LCD TV, simply because the CRT’s analogue nature smoothes out edges and hides compression. Similarly, old games will look much smoother on an old CRT TV than they will on a current PC monitor.

Bogost has some screenshots of Enduro, Pac-Man and Yars’ Revenge that demonstrate the CRT emulation in action, which you can see below. According to Bogost, the team is now working with the guys who maintain Stella to patch the CRT emulation changes into the build. Bogost also says that he’s “hopeful that this software might be extended for use in other emulators for computer systems that used televisions as their primary output.”

Although plenty of other emulators offer primitive CRT TV emulation, this is the first time we’ve seen a concerted effort to really reproduce the quirks of an old CRT TV on a modern computer. Are the effects of a CRT TV needed to fully appreciate retro games, or would you rather have the clean colours and pixels of an LCD? Which other emulators would you like to see using technology such as this? Let us know your thoughts in the forums.

Via The Register.

CRT emulation provides authentic retro gaming
Pac-Man - Note the afterimage effect on the flickering ghosts.

CRT emulation provides authentic retro gaming
Enduro - Bogost says that the bleeding between the multiple coloured lines in the sunset makes the sky more realistic.

CRT emulation provides authentic retro gaming
Yars' Revenge - The scanlines give the image a textured feel, rather than simple flat pixels.

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