Question about Atari 5200 resolution

[Airwolf]

Hi, I've read about the resolution of the Atari 5200 being 316x192, however the Atari pixels were rectangular if my memory serves me right, so, in order to get accurate screenshots of Atari 5200 games, which PC pixel resolution should they be? 320x200?

 

Thanx in advance.

[Rybags]

The 5200 (and 8-bit computers) hires display is "half-VGA" resolution.

 

ie - 320x240 in "full-screen", where a display is generated which covers almost all of a standard TV.

 

The actual visible resolution which can be generated is 352x240 but 20+ horizontal pixels will not be visible on most TVs.

 

The monochrome hires pixels are square, or at least very close to it.

 

Ed: PAL is slightly different - since the vertical TV resolution has an extra 50 scanlines per fiels, PAL Ataris have small black borders at the top and bottom of screen, which causes the pixels to be slightly shorter.

Edited April 12, 2006 by Rybags

[JB]

The 5200 doesn't have a single resolution.

 

There's several possible horizontal resolutions depending on what video mode a given line is in.

And the ability to mix video modes means there's an even larger number of possible vertical resolutions.

 

Arguably, the highest resolution possible is the best, as it means the resampling artifacts are smaller.

Alternately, you could use an emulator that allows you to disable image scaling and then resize the raw image to a 4:3 resolution in an image editor program. Image editors should have better resampling routines as they need quality instead of speed.

 

 

 

Of course, if everything can be represented at 320*240, that's the optimum resolution. But I don't think the pixel sizes are all representable at that res.

Edited April 12, 2006 by JB

[Rybags]

It's probably best to try different resolutions if using video capture.

 

In my experience, capture cards show most of the overscan area, so 352x288 might best reproduce an Atari screen (on a PAL system).

Edited April 12, 2006 by Rybags

[ZylonBane]

The 5200 (and 8-bit computers) hires display is "half-VGA" resolution.

 

ie - 320x240 in "full-screen", where a display is generated which covers almost all of a standard TV.

No, it's 320x200 (NTSC). The pixel aspect ratio is different. This is why native-resolution screenshots looks slightly squashed when viewed on a PC.

[Rybags]

No, a full Display List can do 240 scanlines.

 

Virtually all computers have the same vertical resolution anyway (re size), since they have to conform to the capability of legacy PAL and NTSC TVs.

 

Incorrect aspect ratio is just a case of emulation not doing the correct amount of overscan.

[ZylonBane]

No, a full Display List can do 240 scanlines.

Most of which are invisible on a standard TV. In fact, on the 8-bit computer line all the built-in modes are only 192 scanlines high. Anything taller than that was judged too likely to be lost to overscan.

 

And I don't think "aspect ratio" means what you think it means.

[vdub_bobby]

No, a full Display List can do 240 scanlines.

Most of which are invisible on a standard TV.

I know what you mean, but this amused me anyway.

 

"Most" of the 240 scanlines are invisible? So, what, a standard TV can only display <120 scanlines?

 

AFAIK, most (NTSC) TVs can display 200 or more scanlines.

Edited April 13, 2006 by vdub_bobby

[Rybags]

Older TVs tended to hide a lot of the overscan area compared to modern ones.

 

In my experience (although on PAL), I've found that only the top and bottom characters get clipped if you have a "real" fullscreen DLIST, and that was on old TVs with poor picture coverage.

 

A standard TV has a aspect ratio of 4:3 (h:v), which translates perfectly to 320:240.

 

The incorrect aspect ratio I referred to was referring to is the fact that some emulators do fullscreen in 320x200, which means they are stretched if viewed on a PC monitor.

 

The Atari pixels probably aren't exactly square, it varies slightly depending on the TV. But they're so close that it doesn't really matter anyway.

[ZylonBane]

The incorrect aspect ratio I referred to was referring to is the fact that some emulators do fullscreen in 320x200, which means they are stretched if viewed on a PC monitor.

And this stretching is correct, for exactly the reason you cited-- due to NTSC overscan, a 200-scanline display should fill the screen. AtariAge even used to vertically stretch all their Rarity Guide screenshots, so they would appear proportionally correct when viewed on a PC.

 

It's kind of a shame that the concept of overscan has been lost in modern computer graphics. Now nothing penetrates that black border around the edge.

[JB]

A standard TV has a aspect ratio of 4:3 (h:v), which translates perfectly to 320:240.

 

The incorrect aspect ratio I referred to was referring to is the fact that some emulators do fullscreen in 320x200, which means they are stretched if viewed on a PC monitor.

 

The Atari pixels probably aren't exactly square, it varies slightly depending on the TV. But they're so close that it doesn't really matter anyway.

Actually, I'm pretty sure the pixels AREN'T supposed to be square.

 

It's kind of a shame that the concept of overscan has been lost in modern computer graphics. Now nothing penetrates that black border around the edge.

No. A properly adjusted display, of any type, has image going to EXACTLY the edge of the display. No further, no less.

The death of overscan is a glorious thing, and I wish it would fall in all fields instead of merely the computer industry.

 

 

Overscan compensation only existed on the early home computers because they were outputting to TV screens.

Those TV screens were massively misadjusted INTENTIONALLY at the factory because it was easier to drive the image off the edge of the screen in all directions than it was to properly calibrate the displays. The result is that part of any standard NTSC image will fall outside the edges of the screen, and which parts are missing will vary wildly from set to set.

 

As soon as computers moved to dedicated monitors with user-accessable size and centering controls, compensating for overscan ended. The ability of the end user to adjust the screen meant display manufacturers could be cheap and lazy them without screwing the image up for everyone.

There was no longer a REASON to leave a full quarter of your display blank because you had no idea how much of it would be cropped by an out-of-spec display or in which direction it would be hit worst.

 

 

 

Tangentally-related, very old TVs HAD user-accessable size and centering controls. They were hidden in later models to "dumb down" the sets for the lowest common denominator(IE: a brain-dead moron that won't open the manual and is afraid of anything he doesn't think he understands).

[ZylonBane]

The death of overscan is a glorious thing, and I wish it would fall in all fields instead of merely the computer industry.

Wrong, of course. Unlike the old Atari/Commode/etc, modern OSs use the entire available screen resolution, so you can't adjust your display out to the very absolute edge of the screen without clipping off part of the interface. Well-defined overscan lets you guarantee that all the important stuff will stay onscreen, while also allowing the entire display to be filled.

[Bryan]

Early computers allowed for quite a bit of border area to ensure compatibility with the most TV sets. It's excessive in most cases, and Castle Crisis uses a screen that's 210 lines tall.

 

-Bry

[JB]

The death of overscan is a glorious thing, and I wish it would fall in all fields instead of merely the computer industry.

Wrong, of course.

If by wrong, you mean right.

 

Unlike the old Atari/Commode/etc, modern OSs use the entire available screen resolution, so you can't adjust your display out to the very absolute edge of the screen without clipping off part of the interface.

That is completely, entirely, 100% wrong.

 

 

A properly adjusted display has the image end EXACTLY at the edge of the screen. No data is lost. As I said the first time, and you have chosen to ignore.

 

A modern computer app uses the entire screen because a computer monitor is more than likely properly adjusted, and if it's misadjusted, it's user-fixable. There's no need to compensate for what amounts to intentional manufacturing defects.

 

With the rise of LCD monitors it's even easier, as all addressable pixels are within the visible area and the computer sends the image digitally to the display, so it addresses the pixels directly.

 

Well-defined overscan lets you guarantee that all the important stuff will stay onscreen, while also allowing the entire display to be filled.

No.

Overscan compensation(which is not the same thing as overscan) prevents the entire display from being filled by adding grossly large deadzones to ensure that displays featuring a wide variety of misadjustments all show the full image(and it even fails at that, as many displays feature enough overscan to chop through overscan compensation and into the image in one direction).

 

Overscan's entire reason for being prevents it from being well-defined.

 

 

And I'm dropping this now. I've corrected most of the insane drivel you've spewed, so you won't confuse anyone with what I can only assume are intentionally misleading comments.

[ZylonBane]

A properly adjusted display has the image end EXACTLY at the edge of the screen. No data is lost. As I said the first time, and you have chosen to ignore.

Yes, life is simpler when you ignore silly pie-in-the-sky idealism.

 

I have never in my life seen a monitor which has its display EXACTLY aligned with the edges of the viewable area. Not even LCDs. It's a quaint dream, but that sort of pixel-perfect precision just doesn't happen. So given that there will be error in the alignment process, it's smartest to err on the side of being able to see the entire generated image... and hence, a black border, albeit a very small one.

[SeaGtGruff]

Overscan compensation only existed on the early home computers because they were outputting to TV screens.

Those TV screens were massively misadjusted INTENTIONALLY at the factory because it was easier to drive the image off the edge of the screen in all directions than it was to properly calibrate the displays. The result is that part of any standard NTSC image will fall outside the edges of the screen, and which parts are missing will vary wildly from set to set.

 

Something I once read in an article on the internet made it sound like one reason for overscanning the TV picture was so people wouldn't complain to TV manufacturers that their sets were "defective" because there were black areas at the edges of the screen where the picture wouldn't display!

 

Tangentally-related, very old TVs HAD user-accessable size and centering controls. They were hidden in later models to "dumb down" the sets for the lowest common denominator(IE: a brain-dead moron that won't open the manual and is afraid of anything he doesn't think he understands).

 

When I was a kid, our family had TV sets with controls in the back for adjusting the horizontal and vertical picture dimensions. The way I remember it, we even had one set with separate adjustments for the three electron beams for the red, green, and blue pixels! I don't remember if I could adjust the convergence of the beams, but I remember being able to adjust their intensities. The red, green, and blue adjustments were recessed into holes in the casing so they couldn't be adjusted "by hand," but they could be adjusted with a flat-head screwdriver. On the other hand, the knobs for the vertical and horizontal adjustments stuck out and could be easily twisted with one's fingers, but they were still hidden in the back. The way I remember it, these controls in the back were in addition to the usual brightness, contrast, and tint controls on the front of the set.

 

Michael Rideout

[JB]

Overscan compensation only existed on the early home computers because they were outputting to TV screens.

Those TV screens were massively misadjusted INTENTIONALLY at the factory because it was easier to drive the image off the edge of the screen in all directions than it was to properly calibrate the displays. The result is that part of any standard NTSC image will fall outside the edges of the screen, and which parts are missing will vary wildly from set to set.

 

Something I once read in an article on the internet made it sound like one reason for overscanning the TV picture was so people wouldn't complain to TV manufacturers that their sets were "defective" because there were black areas at the edges of the screen where the picture wouldn't display!

That's part of it.

 

But rather than take the time to properly calibrate the set so the image was centered and the right size, they just blew it up enough to ensure the edges of the image fell outside all 4 edges of the picture tube.

It was easy, it was simple, and it guaranteed no one would ever see black borders. Or all of the picture.

It was, in short, the WRONG way to fix the problem.

 

Tangentally-related, very old TVs HAD user-accessable size and centering controls. They were hidden in later models to "dumb down" the sets for the lowest common denominator(IE: a brain-dead moron that won't open the manual and is afraid of anything he doesn't think he understands).

 

When I was a kid, our family had TV sets with controls in the back for adjusting the horizontal and vertical picture dimensions. The way I remember it, we even had one set with separate adjustments for the three electron beams for the red, green, and blue pixels! I don't remember if I could adjust the convergence of the beams, but I remember being able to adjust their intensities. The red, green, and blue adjustments were recessed into holes in the casing so they couldn't be adjusted "by hand," but they could be adjusted with a flat-head screwdriver. On the other hand, the knobs for the vertical and horizontal adjustments stuck out and could be easily twisted with one's fingers, but they were still hidden in the back. The way I remember it, these controls in the back were in addition to the usual brightness, contrast, and tint controls on the front of the set.

The one I had with those knobs was a black+white I got from my grandmother. It had all the picture controls in the back, if I recall.

[Bryan]

I have to wonder what the original NTSC spec was for overscanning. How far off the edges were the blanks supposed to occur?

 

-Bry

[JB]

I have to wonder what the original NTSC spec was for overscanning. How far off the edges were the blanks supposed to occur?

 

-Bry

As far as I know, there isn't any.

 

I know there isn't any in the vertical axis. All 480 visible lines are supposed to be, well, visible.

[Bryan]

I have to wonder what the original NTSC spec was for overscanning. How far off the edges were the blanks supposed to occur?

 

-Bry

As far as I know, there isn't any.

 

I know there isn't any in the vertical axis. All 480 visible lines are supposed to be, well, visible.

 

Since traditional tubes aren't square, you can't line things up perfectly. Either you have some missing screen or visible black area. I thought a figure of 10% or so was the standard.

 

-Bry

[JB]

I have to wonder what the original NTSC spec was for overscanning. How far off the edges were the blanks supposed to occur?

 

-Bry

As far as I know, there isn't any.

 

I know there isn't any in the vertical axis. All 480 visible lines are supposed to be, well, visible.

 

Since traditional tubes aren't square, you can't line things up perfectly. Either you have some missing screen or visible black area. I thought a figure of 10% or so was the standard.

 

-Bry

The visible image area IS square(well, rectangular). It's possible to adjust for exact transition, and I do it with all my monitors.

Sometimes it takes a good bit of fidgeting with geometry controls, though. And viewing location does matter. The thickness of the glass means that the apparent location of the phosphors changes with your location.

...

I really should dig out the service code and fix my main TV's scan area. .

 

The "standard" overscan area on a mass-market TV is roughly 20-25% of the total image area. So about 12% per axis, or 6% a side, assuming a centered image.

But it's never going to be the SAME 20-25%, because no manufacturer bothers to actually center the image. Heck, I've seen TVs that show one edge of the image and the space beyond it DESPITE the overscan (mis)configuration.

 

 

TV broadcasters usually take overscan into account and position their logos and information scrolls well inside the image to ensure they aren't cropped. But I have seen them assume too little overscan and lose (sometimes important) information.

[supercat]

A properly adjusted display has the image end EXACTLY at the edge of the screen. No data is lost. As I said the first time, and you have chosen to ignore.

For a variety of reasons, that isn't quite true. The edge of the visible portion of the phosphor screen may be affected by things like viewing angle; it is thus impossible to adjust the image to precisely fill the screen under some viewing conditions without clipping the edge under other conditions.

 

A modern computer app uses the entire screen because a computer monitor is more than likely properly adjusted, and if it's misadjusted, it's user-fixable. There's no need to compensate for what amounts to intentional manufacturing defects.

There is no need to have an overscan area that's nearly as large as what used to be common. Nonetheless, there is still 'some'. It would be useful in some applications to be able to fill it with non-critical data (e.g. have the OS 'full screen' size used for the placement of fixed objects or zoomed windows be inset from the programmable screen region while stretching things like wallpaper out to the edge.

[supercat]

I have to wonder what the original NTSC spec was for overscanning. How far off the edges were the blanks supposed to occur?

 

A television set must not display line 21 or above of a field, nor may it display the last line. A properly-adjusted set should display, at minimum, the central 192 lines.

 

Professional cameras used for television or modern cinema have two rectangles in their viewfinders. One rectangle (which may be the edge of the viewfinder) shows the entire image that will be photographed or recorded; an inner rectangle marks the portion of the image which is guaranteed to appear on any properly-adjusted set. When setting up a shot, anything which should be seen should be located within the inner rectangle, and anything that should not be seen should be outside the outer rectangle. Things between the two rectangles may or may not be seen.

 

As for the question of why overscan exists, I would offer at least two reasons:

 

-1- If an image fills up the front of a 12"-diagonal tube, the vendor can call his unit a 12" television set. If the image only filled up a 10" rectangle on the front of a 12" tube, it might have to call the unit a 10" set.

 

-2- For a display to look good, either all four edges should be clipped by the panel bezel, or none should. Unfortunately, if factory techs adjust a television so the edges of the produced image are very close to the bezel, calibration drift will very likely cause edges that were covered by the bezel to stop being so, or those that weren't to become so.

[supercat]

It was, in short, the WRONG way to fix the problem.

 

What would have been the "right" way, given that image size could probably be affected by 5% if not more as a result of changing temperature, etc.?

[JB]

It was, in short, the WRONG way to fix the problem.

 

What would have been the "right" way, given that image size could probably be affected by 5% if not more as a result of changing temperature, etc.?

IMO, user-adjustable size and position was the right solution.

 

Of ocurse, it ceases to be an issue with LCD, DLP, ETC. Since there's no signifigant variance in pixel locations, it's easy to make them all visible.