Dungeon Master 2 Aspect Ratio in DOS VGA, Amiga PAL and NTSC with Photos

[ZalewaPL]

Intro

This week I started uploading gameplay footage from Dungeon Master 2 for Amiga. For convenience, I don't grab the actual hardware, but rely on the emulators: DOSBox for DOS and WinUAE for Amiga. I also pay attention to not misrepresent the original graphics of the game: I take care to maintain the correct aspect ratio to avoid distortions and I crop any "black belts" at the edges of the screen. I came to trust the emulators over the years as I grabbed footage from many games with them, but now I think I did not fully understand what they are doing with the intended graphics display of the games.

But, back to the videos: to double-check if my recording is not distorted I sometimes look for shapes that I know should be a perfect circle or a perfect square and confirm that they are indeed so. In case of Dungeon Master 2, I relied on the inventory screen slots and attack icons to be perfect squares. I also check if the in-game mouse cursor moves with equal sensitivity in both the vertical and horizontal directions.

Things seemed good, the squares checked out, but this time, I might've been off.

Here's the screencap of the game's main menu, taken straight from my video:

Screengrab from my video - DM2 in Amiga emulation via WinUAE 1728x1080

2 videos recorded and uploaded, and I get a message from my pixel-perfectionist friend informing me that the picture in my videos is le bad:

• the castle in the background is squashed,
• the game logo is stretched wide,
• and the options pole is too thick.

He can tell those things without a reference.

First of all, I think that the main menu is the best to use here for comparisons because it covers the whole "rendering area" of the game, whereas the gameplay screen leaves some black space at the bottom for the "Torham has gained a Ninja level" texts.

About the Resolution of My Recordings

The screenshot from my video is 1728x1080 pixels. The game doesn't run in this resolution, of course, but I do some upscaling both with WinUAE and with the recording software to make sure the resolution is "pulled-up" to FullHD height-wise, but I don't muck with the aspect ratio. I also prefer to upscale without filtering as much as possible to maintain the square crispness of the pixels (no bilinear filtering). The original resolution in WinUAE, before all the upscaling, is 640x400. This gives an aspect ratio of 16:10. I upscale this by 2 to 1280x800 in WinUAE without filtering, then upscale it to 1728x1080 with the recording software, this time with filtering (the pixels get slightly blurry, but not distorted). 1728x1080 is the same aspect ratio of 16:10 as 640x400, so everything should be okay, right? Right?! Well, no...

The problem is that the ratio most likely shouldn't be 16:10 in the first place.

To the Point

I own some ye olde hardware and did some comparisons. I'm purposefuly sharing photographs taken by phone, not screenshots, because I want to be sure that everyone is seeing what I am seeing. Also, the exact measurements and units are not that important, only the proportions are. Pardon my sloppy photography too.

Photographs of CRT Displays

This comes from a Pentium 133 MHz PC running FreeDOS:

PC FreeDOS VGA 4:3

Already, the ratio is completely different. It's 4:3 now, not 16:10. Also, you can see that the game's graphics fill the whole screen. So, is this correct? Is this "not distorted"?? Is this what I should be aiming for???

Let's see with a real Amiga 1200 with a PAL CRT Television screen:

CRT TV Amiga 1200 RGB PAL

We're back to square one! On the screencap I've written a strange ratio of 16:9.5 because 16:9 and 16:10 are close to each other and my measurements were probably too inaccurate (or the TV just displays that way). With this ratio we're back to how I see things in WinUAE, and far away from the PC's 4:3. Is the game's ratio supposed to be different on Amiga than what it is on PC?

Then I remembered something. FTL were based in US, right? And I live in Poland, Europe. Different TV standards: NTSC in US and PAL where I live. NTSC is "slightly" shorter height-wise than PAL. Fortunately, Amiga can be switched to NTSC at boot, and for some reason (that I can't explain due to the lack of technical knowledge), my TV can take that.

So, let's check Amiga 1200 booted into NTSC mode with a CRT Television:

CRT TV Amiga 1200 RGB NTSC

Great success! The screen is filled whole, and the ratio is 4:3, the same as PC. I played around in the game proper a bit in this mode and there are no new distortions. Is this the right way to play, then?

Game's Box

Well, we can take a look at one more thing. The game's logo, which is also on game's box. One disclaimer though: this is a box for Polish distribution of the game for the PC. Not sure how consistent it is with other distributions of the game.

Various measurements of the game's logo

Uh, okay, this is all over the place. I measured the logo from the leftmost of the 'D' straight right to the end of the 'n' letter, and from the topmost of the 'D' straight down to the bottom of the 'm' (in master). NTSC and VGA measurements look consistent, but boxart is off (or rather: simply different).

But, the box has a backside where screenshots from the game are shown:

Screenshots on the back of the box

At a glance, the screenshots don't look horribly distorted. The inventory icons (hands) are square.

So, let's have some measurements of the screenshot on the back of the box:

Boxback screenshot measured

One thing to note here is that the screenshots on the box don't include the "Torham has gained Ninja level" black area, but this area is about as tall as the movement control arrow, so I doctored the picture a bit and added the height of the arrow (0.4cm) to the whole height of the screen (3cm). The ratio on the box is close to 16:10 again. So, if the ratio on the PC is 4:3, the screens on the box for the PC don't match. It might just be that the screens on the box are not a good reference for the developer's intention, so let's move on.

Emulators

I confirmed that the game renders in 4:3 in DOSBox, provided you configure it with aspect=true. Look:

DOSBox rendering in 4:3

Okay, so let's try NTSC mode in WinUAE emulation. Emulated Amiga can be booted into NTSC mode in the same way that the real Amiga can. Here are two photos with PAL and NTSC modes:

WinUAE with PAL and WinUAE with NTSC

The NTSC resolution is 640x475 for some reason, but that's close enough to 4:3. Is the problem solved, then? We can now just upscale this by 2 to maintain pixel crispness, which will give us a resolution of 1280x950, and we're good to go, right? Right?! Well, there's a price to pay. Here comes a WinUAE NTSC screenshot with some text:

WinUAE in NTSC mode with visible horizontal line distortions (this time a real screenshot)

On this pic you can see pixels duplicated vertically on some of the horizontal lines. Compare the "ROBLP" savegame names and notice that none of the 3 look the same.

Conclusions

Keep in mind that my goal is to have correct results in the emulator, not the real hardware. If I wish to maintain both crisp pixels and 4:3 ratio, the horizontal line distortions ("ROBLP") will be visible throughout the game in many different areas. It's possible to get rid of these distortions by enabling bilinear filtering in WinUAE's "Filter" section, but then the whole image becomes blurry, which to me looks awful.

So, I can choose from only 2 of the 3:

• the "intended" 4:3 aspect ratio,
• pixel crispness,
• no horizontal-line distortions.

In 16:10 I get both pixel crispness and no horizontal distortions, but not the seemingly intended aspect ratio (obviously). The game looks ok in 16:10, as nothing in particular in the game gets too thicc (aside from the Skullkeep castle in the main menu).

When it comes to the CRT and why it does it well: CRT can just stretch 16:10 graphics to 4:3 vertically without distortions because, well, it's a CRT. All the pixels on screen simply get slightly elongated height-wise, which is not that noticeable to the naked eye, and thus the picture still looks OK, even if the actual rendering surface of the game is 16:10. LCD displays can't do that, and the rendering surfaces of emulators most definitely can't do that either without extra filtering.

Unless there is a better method to do this, at this point I'd rather prefer to stay at the supposedly wrong 16:10 ratio and don't have any blurry or distorted pixels.

Extra info tidbit on DOS games rendered in 16:10 and stretched to 4:3

My knowledge is spotty here, so there will be omissions. From what I know, the process of rendering a DOS game to an in-memory surface of resolution 320x200 (which is ratio 16:10) was not uncommon back in the day. One of the reasons this was done was because such 320x200 surface fit into a 64KB of RAM. Check this out: https://doomwiki.org/wiki/Aspect_ratio

The game, rendered to 320x200 (16:10), was then elongated vertically to a 4:3 ratio when displayed (think scaling up from 320x200 to 320x240). What I don't know here is how exactly was this done? Which piece of hardware was responsible for doing this, and why specifically there are no visual artifact? Also, why not just display the view letterboxed? Perhaps it was considered that it's better to fill the whole screen because the user has paid for the whole screen.

There's some discussion about this on Doomworld forums, but I didn't sift through all the posts, yet:
https://www.doomworld.com/forum/topic/9 ... stretched/

How does Amiga's Lisa digital graphics chip see it?

Okay, one last photo. My Amiga 1200 is equipped with an Indivision AGA MK2 card which is inserted over the computer's Lisa graphics chip (which is connected in the circuitry before the Scart-RGB DAC). Indivision allows to connect the computer to a modern screen directly via a DVI cable (or DVI-to-HDMI).

This is what I see on an LCD screen when I boot the Amiga in NTSC mode and run the game:

Amiga Indivision AGA MK2 DVI screen booted in NTSC mode

Yeah, it's 16:10. And also if I boot the computer in the PAL mode, I see the same thing. 16:10 throughout.

P.S.

I've been running around my flat with measuring tapes all Saturday since 10:00 AM and now, in the evening, as I conclude this post and press Submit, my Saturday is officially ruined.

[Gambit37]

This is the sort of thing that interests me and I can help with, but I can't see your images because Imgur now prevent UK users from viewing any content. Would it be possible for you to host the images elsewhere? Many thanks.

[ZalewaPL]

I did not know about that. Which host suits you?

[Gambit37]

Any other image host should be fine. Another user recently had success with https://postimages.org/
Note that I'm off to bed now -- I can look at this tomorrow.

[ZalewaPL]

I replaced all imgur links with postimg.cc. Hope it's good now. I'll remember not to use imgur in the future. Also, that's the first time I created a git repo for a PHPBB post, geez.

Also, on topic: the website says that DM2 for Amiga was released in Europe only. So, if the intended visuals are 4:3, they did not adapt the game to PAL resolutions, even though the game was released only in the PAL region. Figures

[ChristopheF]

I looked into that issue of aspect ratio a long time ago, because all the screenshots on the Encyclopaedia are "wrong" in that they do not reflect what one saw on the original hardware.
When DM2 was released in 1995, it was designed for screens with a 4:3 aspect ratio (in centimeters) that was common on most platforms and TV, but the game images consist of 320x200 pixels, meaning a 16:10 aspect ratio (in pixels).

So if you want it all:
- the "intended" 4:3 aspect ratio
- pixel crispness
- no horizontal-line distortions

then you must find a way to upscale the original 320x200 pixels to a larger resolution that must:
- have a 4:3 aspect ratio: number of horizontal pixels / number of vertical pixels = 4:3 = 1.33
- pixel crispness: apply no filtering whatsoever, like bilinear or any other that can only blur and or distort the image
- no horizontal or vertical line distortions: each pixel from the source 320x200 must be replaced by an exact integer number of pixels both horizontally and vertically

The smallest resolution that matches the criteria is 1600x1200 pixels.
You copy each pixel from the source 320x200 image to 5 pixels horizontally and 6 pixels vertically.
You then get 320 * 5 = 1600 pixels horizontally, and 200 * 6 = 1200 vertically.
If you don't apply any filtering pixel crispness is perfect
You get an aspect ratio of 1600 / 1200 = 4:3 = 1.33

One option for you might be to configure WinUAE to output 320x200 pixels (by configuring WinUAE Host/Display settings: Resolution = LoRes, and Line mode = Single), then use you recording software to upscale the 320x200 output to 1600x1200 (again without applying any filter).


For the record, this 320x200 screen resolution is the same for DM, CSB and DM2 on all platforms except for Dungeon Master on the Super Nintendo where the screen resolution is 256x224.
The smallest screen resolution meeting all critera is 256 * 7 = 1792 horizontal pixels and 224 * 6 = 1344 vertical pixels.
Aspect ratio is 1792/1344 = 4:3 = 1.33

[Gambit37]

Thanks Christophe, you beat me to it and of course are absolutely correct.
One thing to note is that although it's implied in Christophe's info above, it's not explicitly stated:

Pixels back in the day were not square, they were 1.2 times taller than wide.

(Although, that did depend on how the user had set the vertical scale on their CRT.)

Hence the smallest multiple of 320x200 at 4:3 ratio is 1600x1200. I put an example of a stretched DM image in this thread if you're interested:

viewtopic.php?t=31300

It's also my understanding that the Atari ST ran at 320x200, but the Amiga ran at 320x256 if I recall, with a much taller empty black space at the bottom of the screen. I'd assume this resulted in a slight difference to the perceived aspect ratio of games on these two platforms, depending how the user adjusted the vertical hold on their CRT TV. This could all be me misremembering though.

Incidentally, the 1.2 vertical scale factor is why many modern games played in modern source ports or emulators often look wrong. Quake for example, a game I've returned to playing over the last two years, looks very wrong in most modern source ports. Textures and 3D geometry that were designed to look circular now look squashed vertically. It can be fixed with various tweaks, but it's something to be aware of.

[ZalewaPL]

Games with 3D projection are easier to adapt to different formats because the game can just render more (or less) of the game world, and "elongation" of game objects can be emulated with even more projection. If a 3D shooter was intended for a 4:3 screen and you run it on a 16:9, you will simply see more to the left and right. The UI elements in those games are usually minimal and placed in known locations, so modern source ports have easier time adapting them visually. It's not the same story as when the whole game is 2D.

More on topic, though: first of all, thank you guys. ChristopheF's tip to start at 1600x1200 and work from there helped a lot. Once I got the grasp of what was happening, the method to replicate the aspect ratio correction in a recording, and then get it to a resolution that YouTube likes (1080p), was easy to devise. I think I have a sound solution to record a 16:10 screen in the 4:3 ratio now with satisfying visual quality.

WinUAE upscaled to 1440x1080 without artifacts and with crispness:


But I'm still not convinced if I should even do that. I mean, if the original PAL Amiga user would see a vertically squished screen, should I really change it to PC's 4:3 when recording Amiga gameplay "faithfully"? The manuals available on dmweb don't say anything about switching the Amiga to NTSC for the game.

[Gambit37]

If a 3D shooter was intended for a 4:3 screen and you run it on a 16:9, you will simply see more to the left and right.

True, but that's not what I was referring to. Quake had actual "squashed" circular geometry and similarly squashed textures for the circular windows and archways: these were scaled down by a factor of 1.2 on the vertical in their design to compensate for the stretched pixels of the target display.

WinUAE upscaled to 1440x1080 without artifacts and with crispness:

This is perfect, nice job

But I'm still not convinced if I should even do that. I mean, if the original PAL Amiga user would see a vertically squished screen, should I really change it to PC's 4:3 when recording Amiga gameplay "faithfully"? The manuals available on dmweb don't say anything about switching the Amiga to NTSC for the game.

I played DM on a PAL Amiga back in the day and I don't recall a squashed screen. It looked like the screenshot in that other thread I linked to. However, I do very clearly recall fiddling with the vertical stretch on the CRT controls, so it's possible I cranked it beyond a typical/default setting...

I presume DM2 on the Amiga worked the same way, but I didn't play DM2 until much later on the PC.

[ZalewaPL]

recall fiddling with the vertical stretch on the CRT controls

I completely forgot that was the thing.

For those who come after:
https://www.amigalove.com/viewtopic.php?t=38

[Gambit37]

Thanks for the link ZalewaPl, I've read that thread before, but it's good to review it again. What a mess this retro hobby has made for itself!

(Also, it's unfortunate that the screenshots on that page are all on Imgur. Now I can't see any of them. Looks like I'm gonna have to start using a VPN to get around that.)

EDIT: NordVPN have an incredible Black Friday sale on, so I just took advantage of that and suddenly the web is open again!