7800-emulation/real-resolution-issues

[108 Stars]

Hi! I have a bit of a problem; I am a mod on a website similar to Moby Games called TheLegacy. Every registered member can support us with information and screenshots, and it is my job to control them and either accept them if they meet the criteria or to refuse to take them if they don´t. The most important criteria is that it should be original; no filters and no upscaling.

Lately more screenshots for Atari-systems have been sent, and I find myself in a bit of trouble with Atari 7800 screenshots. The problem is the resolution.

 

There are varying suggestions about resolutions.

Possible resolutions I read about:

 

160x240

160×242 (PAL?)

160x288 (PAL?)

320×242 (PAL?)

320×288

320x240

320x200

 

Probably there are even more resolutions rumored somewhere.

Now I honestly don´t know what to do with 7800-screenshots. Are all these resolutions possible? If not, which are wrong? Or are they all correct and possibly more variants missing?

 

The screenshots on AtariAge are always upscaled, so no good reference. Even assuming they are just doubled in size, for example the 640x446 pics of Food Fight would suggest the original resolution was 320x223, meaning yet another bizarre resolution.

 

Many specialists around here, so please help me.

And I´d like to tell our supporters how to best get correct screenshots; which emulator allows settings using the original resolution? Or at least just with a frame I can cut off manually?

 

Thx in advance!

Edited October 26, 2009 by 108 Stars

[gdement]

Horizontal can be either 160 or 320. Both modes are possible. Also, the resolution can change mid-screen. Many games have 320 resolution in a status bar area (for text), then drop to 160 resolution for the gameplay area (160 mode is faster and more colorful). I imagine emulator screenshots would all be rendered as 320 pixels though.

Actually, since the 7800 pixels aren't square, the emulators might upscale them to look correct on a computer monitor, so getting 1:1 pixel screenshots might be a problem.

 

The vertical resolution is technically 243 lines (from the "7800 Software Guide").

According to something I found in some code, I think the PAL output is 293 lines.

 

This exceeds what will actually fit on a CRT television, so only part of it is normally used. Exactly how many lines get used would be up to the programming. That's why vertical might be different with almost every game.

 

Unused scanlines would be blank, I don't know if the emulators actually detect this and crop them out of the image, but maybe so.

 

So basically, the theoretical resolution is 320x243 NTSC, 320x293 PAL.

 

In practice, most scanlines in most games will be rendered with double-wide pixels, and only about 192-200 or so (NTSC) scanlines are reliably visible on all televisions.

 

 

[edit: added PAL info]

Edited October 26, 2009 by gdement

[108 Stars]

Ungh...that basically means that it´s pretty much impossible to make a general statement about the resolution and that I´d best accept everything around 320 x something.

 

Okay, thank you, that will have to do then.

[kool kitty89]

Ungh...that basically means that it´s pretty much impossible to make a general statement about the resolution and that I´d best accept everything around 320 x something.

 

Okay, thank you, that will have to do then.

 

If I may add a bit more on these displays in general:

There's 2 horizontal resolutions that can be used and a fixed number of lines desplayed by the TV for the vertical resolution (same for anything else outputting to an SDTV). NTSC displays 480i- 480 interlaced lines (in 2 "fields") at 60 Hz (with a total of 525 lines extending into overscan). Old game consoles (and contemporary home computers) output with the 2 fields overlapping, producing a 240 line noninterlaced display (240p), and for PAL a 576i 50 Hz display with 288p displayed. (in practice far less lines are visible, particularly NTSC ones, with newer TVs usually displaying 448i/224p lines and even less for some really old TVs, some newer PAL TVs and HDTVs can have almost no overscan, showing almost all lines, as will some somewhat older, tightly calibrated TVs)

 

In any case, it's the horizontal resolution that's variable and dependedent on the console, with vertical resolution only able to be "clipped" using fewer lines for display, which will look like letterboxing on the TV -excep parts clipped in overscan. (the 2600 used 192 lines IIRC -several others used this as well) Consoles line the SNES/NES/Genesis tended to clip the display to 224 lines, though there are also cases of far more clipped displays bein used. (like Virtua Racing on the Genesis)

Edited October 27, 2009 by kool kitty89