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shoober

PrBoom+ vs Chocolate Doom Fake Contrast

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I have been comparing PrBoom+ and Chocolate Doom for about a week now, and haven't noticed any differences using the software render, except for one. PrBoom+'s fake contrast is stronger then Chocolate Dooms. PrBoom+'s will light up areas farther away then what Chocolate Doom does. Here is an example:

PrBoom+


Chocolate Doom


On the wall to the left, you can see that in PrBoom+, the wall it completely lit up. But, in Chocolate Doom, it cuts of the fake contrast early and the wall is black. I'm standing in the same spot for each picture. I can safely assume that Chocolate Doom's fake contrast is the correct way and how its supposed to look. Why is PrBoom+'s fake contrast different?

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Does it change something if you put PrBoom+ in the same resolution as Choco?

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Okay, I figured it out. I had to change my aspect ratio back to 4:3 instead of 16:10. Why I used 16:10, was I was trying to use the correct aspect ratio for DOOM. 320x200 is 8:5, or more commonly called 16:10 aspect ratio, so I put PrBoom+ to 16:10 while using a resolution that was in the multiple of 320x200. So I chose 1920x1200. This gave the same appearence as Chocolate Doom, but I just noticed that the fake contrast was all wrong.

Now I'm stuck in a rut. As most of you probably know already, using a 4:3 resolution in DOOM will make it look smooshed, and sandwiched. Playing at 16:10 (DOOM's original aspect ratio) fixes this and makes it look correct. Chocolate Doom has a option to correct the aspect ratio, so no matter what resolution your using, it will correct it to look like it does with 16:10. Also, If you don't use a resolution in the multiple of 320x200 with a 4:3 aspect ratio, the fake contrast will look like it does with 16:10.

What am I to do? How can I get PrBoom+ to correct the aspect ratio without it messing with the fake contrast? I don't think theres an option. I would just simply use Chocolate Doom, but I can't stand using such a low resolution. If Chocolate Doom would let you increase the internal resolution instead of scaling 320x200, it would be a miracle. If there was a source port that was exactly like Chocolate Doom, except it let you increase the internal resolution, I would poop my pants.

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shoober said:

Okay, I figured it out. I had to change my aspect ratio back to 4:3 instead of 16:10. Why I used 16:10, was I was trying to use the correct aspect ratio for DOOM. 320x200 is 8:5, or more commonly called 16:10 aspect ratio, so I put PrBoom+ to 16:10 while using a resolution that was in the multiple of 320x200. So I chose 1920x1200. This gave the same appearence as Chocolate Doom, but I just noticed that the fake contrast was all wrong.

Now I'm stuck in a rut. As most of you probably know already, using a 4:3 resolution in DOOM will make it look smooshed, and sandwiched. Playing at 16:10 (DOOM's original aspect ratio) fixes this and makes it look correct. Chocolate Doom has a option to correct the aspect ratio, so no matter what resolution your using, it will correct it to look like it does with 16:10. Also, If you don't use a resolution in the multiple of 320x200 with a 4:3 aspect ratio, the fake contrast will look like it does with 16:10.

What am I to do? How can I get PrBoom+ to correct the aspect ratio without it messing with the fake contrast? I don't think theres an option. I would just simply use Chocolate Doom, but I can't stand using such a low resolution. If Chocolate Doom would let you increase the internal resolution instead of scaling 320x200, it would be a miracle. If there was a source port that was exactly like Chocolate Doom, except it let you increase the internal resolution, I would poop my pants.


+1 on a chocolate-doom-like port that increases resolution.

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The thing is that if you increase resolution, you'll see farther away (because stuff will not be reduced to "less than a pixel in size, skip" as soon as they do in 320x200). Which leads to, for example, seeing more visplanes. Crash! You've got yourself a VPO on your hands. So you need to raise limits as well.

It's a slippery-slope from that point.

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shoober said:

Now I'm stuck in a rut. As most of you probably know already, using a 4:3 resolution in DOOM will make it look smooshed, and sandwiched. Playing at 16:10 (DOOM's original aspect ratio) fixes this and makes it look correct.

Hi! Doom's aspect ratio is complicated and difficult to understand. Please read the wiki article if you haven't already to properly acquaint yourself. The brief summary is that 4:3 aspect ratio is the correct aspect ratio for Doom; the raw graphics should be stretched slightly in order to look correct. When you enable Chocolate Doom's "fix aspect ratio" option, this is what it does.

I have to admit that looking at your screenshots I find it difficult to see what you mean (they look the same to me), but I don't understand your terminology or what "fake contrast" means.

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Gez said:

The thing is that if you increase resolution, you'll see farther away (because stuff will not be reduced to "less than a pixel in size, skip" as soon as they do in 320x200). Which leads to, for example, seeing more visplanes. Crash! You've got yourself a VPO on your hands. So you need to raise limits as well.

It's a slippery-slope from that point.

You also increase the "signal-to-noise" ratio of the Doom engine for every higher multiple of the native resolution you attempt to render, so the mild problems like jiggly visplanes, warping floor textures, warping linedefs, and "sparkles" at the bottom of textures are increased by about a factor of two for every multiple of 320 you set as a resolution.

This got so bad in Eternity that SoM spent most of his career actively working to erase these problems, first with more accurate span renderers, and then additionally with the Cardboard floating-point renderer. It's an investment of time that few people really grasp.

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fraggle said:

I don't understand your terminology or what "fake contrast" means.

I suppose he's referring to this.

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The way lighting and z-distance is calculated is also resolution dependant...in general it's one of the most complicated/less clear aspects of the vanilla renderer to understand.

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The shape of the brightest spot on the angled wall directly ahead is different, which suggests that they use a different light intensity in the color table lookup. The slight difference quantizes to the doom palette differently.

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Oh I get now. I can see why Boom was created then, which raises the limits on these very things. I'm just trying to figure out how I can get PrBoom+ to look like Chocolate Doom, aspect ratio and fake contrast wise. Technically, 320x200 is a 16:10 ratio, but the Doom engine just displays it at 4:3, so it looks very unique. To mimic this effect, I had to use 16:10 in PrBoom+ to make it look like it does in Chocolate Doom.

I think at the moment it is impossible to have the correct aspect ratio in PrBoom+, while having the same fake contrast as in vanilla Doom. When I choose 4:3 in PrBoom+, the graphics look squashed. Doomguy's face will appear square instead of rectangular like it should. Playing at 4:3 with PrBoom+ looks like the face on the right in this picture. The maps look so strange after you viewed them at there correct aspect ratio. I guess its not that big of a deal until you view the maps the right way, then you don't want to see them any other way.

So what should I do? Should I try and contact the maker of PrBoom+ and ask him to add aspect ratio correction like Chocolate Doom does? Should I just quit being a spoiled brat and play Doom at its original resolution? Its so hard to go back once you played Doom at high resolution. Is there some kind of way to get PrBoom+ to correct the aspect ratio without changing the way fake contrast is used?

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shoober said:

Should I try and contact the maker of PrBoom+ and ask him to add aspect ratio correction like Chocolate Doom does?

Um, what are you talking about? PrBoom+ already does aspect ratio correction. "Like Chocolate Doom" in this context would mean rendering in 320x200, then stretching, and this is what you want to avoid, evidently.

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prboom-plus should already be displaying the correct aspect no matter your monitor. By default it detects the resolution's aspect ratio and adjusts all the graphics accordingly. Go to Options->General and you can change it according to your monitor's proper resolution, though. For example, I use 1920x1200 so I can just set it to 16:10, and all the graphics in the game are stretched appropriately; it's still widescreen, but not incorrectly sized sprites and such.

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Ah, I think I know what's wrong with 4:3 aspect ratio. The monitor is set to fill the entire screen instead of preserving the proportions. This may (or may not) be adjustable via the monitor's own settings panel.

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Da Werecat said:

Um, what are you talking about? PrBoom+ already does aspect ratio correction. "Like Chocolate Doom" in this context would mean rendering in 320x200, then stretching, and this is what you want to avoid, evidently.


The problem is, it doesn't preserve the way fake contrast is supposed to look at 4:3 when you change the aspect ratio. Doom simply displays a 16:10 resolution at 4:3, which is what makes the pixels seem more rectangular then square. PrBoom+ can mimic this look by displaying the game at 16:10, but it doesn't keep the way fake contrast is drawn at 4:3, since it renders at 16:10 instead. So its not EXACTLY doing the aspect ratio correction like Chocolate Doom does.

chungy said:

prboom-plus should already be displaying the correct aspect no matter your monitor. By default it detects the resolution's aspect ratio and adjusts all the graphics accordingly. Go to Options->General and you can change it according to your monitor's proper resolution, though. For example, I use 1920x1200 so I can just set it to 16:10, and all the graphics in the game are stretched appropriately; it's still widescreen, but not incorrectly sized sprites and such.


I already was using 1920x1200 at 16:10. The whole problem and reason I started this thread was because if you use these settings, it will draw the fake contrast incorrectly. See the picture above. It only draws the fake contrast correctly if you use 4:3 at a resolution in the multiple of 320x200. But, as you probably know, if you use 4:3 ratio, it won't be correct the aspect ratio, and everything appears squashed and more square.

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Da Werecat said:

Well, try to force your monitor to display 4:3 with black borders instead of stretching it to fill the screen.


I don't think I can do this, since I have a old school 4:3 CRT monitor. I'm going to open up PrBoom+ a little later and try to use 16:10 and a 4:3 resolution to see if that fixes the fake contrast.

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shoober said:

Doom simply displays a 16:10 resolution at 4:3, which is what makes the pixels seem more rectangular then square.

Technically, Doom displays 16:10 as 16:10, but it was designed for 4:3 CRT displays that would stretch the image vertically. Modern source ports do the stretching themselves, depending on the resolution. 4:3 video modes should work fine on your 4:3 display. I'm not sure why the picture is squashed.

[edit]
Oh wait, are you testing 4:3 in windowed mode with 16:10 resolution?

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Da Werecat said:

4:3 video modes should work fine on your 4:3 display. I'm not sure why the picture is squashed.

[edit]
Oh wait, are you testing 4:3 in windowed mode with 16:10 resolution?


The picture is squashed because its displaying the 320x200 multiple resolution without the stretching. To mimic the stretching, you have to use 16:10.

I went back and tried some things in PrBoom+. First off, it does not correct the aspect ratio like Chocolate Doom does. It just simply says, "Oh, you're using a 4:3 resolution, I will automatically set the ratio to 4:3." Chocolate Doom does this differently. It will draw the original 16:10 320x200 resolution, then display it as 4:3, just like those monitors did back then. I don't know a single engine besides Chocolate Doom that does this kind of aspect ratio correction, while keeping the fake contrast the same as it is in vanilla or chocolate Doom.

When you manually set a 320x200 multiple resolution in PrBoom+, and select 4:3, the image will become stretched. Or, if you set a standard 4:3 resolution, and display it as 16:10, the fake contrast will not be correct. Its a mess. Its just about impossible to have the same aspect ratio while keeping true to the original way fake contrast is drawn in vanilla or Chocolate Doom, unless PrBoom+ adds a option to correct the aspect ratio the way Chocolate Doom does.

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I'm assuming that the answer to my question is "yes".

shoober said:

without the stretching

PrBoom+ applies aspect ratio correction based on settings. You have a 16:10 image displayed on a 16:10 surface. You're telling the engine to apply correction as if the image was displayed on a 4:3 surface. Guess what happens.

shoober said:

To mimic the stretching, you have to use 16:10.

320x200 without the stretching is 16:10.

shoober said:

It just simply says, "Oh, you're using a 4:3 resolution, I will automatically set the ratio to 4:3."

Um, no. It lets you to choose between 4:3, 16:9, 16:10, 5:4, and auto.

shoober said:

When you manually set a 320x200 multiple resolution in PrBoom+, and select 4:3, the image will become stretched.

In windowed mode? Of course it will.

shoober said:

Or, if you set a standard 4:3 resolution, and display it as 16:10...

Why would you do such a thing? Unless you have a 16:10 monitor.

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Da Werecat said:

I'm assuming that the answer to my question is "yes".


Regardless of if I'm in window or fullscreen mode, it doesn't have an effect on whether it stretches or not. The results are the same.

Da Werecat said:

PrBoom+ applies aspect ratio correction based on settings. You have a 16:10 image displayed on a 16:10 surface. You're telling the engine to apply correction as if the image was displayed on a 4:3 surface. Guess what happens.


I already know that it stretches, which is why I was pointing out that it doesn't do aspect ratio correction EXACTLY like Chocolate Doom does. If I threw a 16:10 resolution at Chocolate Doom, it would display it as 4:3 unstretched. This is not how PrBoom+ behaves. They do NOT have the same method of aspect ratio correction.

Da Werecat said:

320x200 without the stretching is 16:10.


Even with the stretching its technically still 16:10. That's not the point. The point was that the graphics are squashed because the 16:10 resolution doesn't have the 4:3 stretching that was originally applied to Doom via the monitor, which Chocolate Doom does.

Da Werecat said:

Um, no. It lets you to choose between 4:3, 16:9, 16:10, 5:4, and auto.


This is what the "Auto" setting does. Oh course you can also do it manually.

Da Werecat said:

In windowed mode? Of course it will.


Fullscreen as well.

Da Werecat said:

Why would you do such a thing? Unless you have a 16:10 monitor.


Because if you don't, the fake contrast will be completely off, which is the whole topic of this thread. I already explained why I was doing this in my previous posts.

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shoober said:

Because if you don't, the fake contrast will be completely off, which is the whole topic of this thread.

I thought you got the "right" fake contrast in multiple of 320x200 (which is 16:10) with forced 4:3 aspect ratio. Now you're telling me it's vice versa. Oh well.

A multiple of 320x200 with forced 4:3 should give you authentic field of view* and square pixels in PrBoom+. Unless you're filling a 4:3 display, in which case it should receive proper stretching. Is your monitor drawing 16:10 resolutions with black stripes? It's the only way things would keep being squashed.

* Note how the first of your shots is wider than the Choco one, even though the proportions are still right. It's not how the game was supposed to look.

shoober said:

They do NOT have the same method of aspect ratio correction.

But they both do aspect ratio correction.

The primary difference is that Choco doesn't screw with your field of view. The picture is always the same, it's always being rendered in 320x200 and then stretched depending on settings.

PrBoom+ actually has different aspect ratios. If you're using a widescreen aspect ratio, you'll get an expanded view. Chocolate Doom in a widescreen resolution will just fill unused space with black.

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The vanilla handling of the light levels and the conversion to the color map give a unique appearance.
This appearance may be familiar but is not really more correct than the display by other ports.

If you played for more than a few days, you would adapt to the new color and brightness appearance and the older vanilla appearance would look strange.
Most people would deny this, but it has been shown that the human vision system has a short memory for these kind of things.

Of more concern is the gamma setting, which determines the light curve, which ultimately determines how much detail you can see in the dark areas. The slightest adjustment of gamma overwhelms any of the little differences you are describing, and every player needs to adjust their gamma to match their monitor. Taking that into account, there is no possible correct appearance to chase after.

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Da Werecat said:

I thought you got the "right" fake contrast in multiple of 320x200 (which is 16:10) with forced 4:3 aspect ratio. Now you're telling me it's vice versa. Oh well.


I ment to say fake contrast, my bad.

I spent some time nailing down how PrBoom+ handles aspect ratio and the fake contrast. Here is what I found. I will copy and paste my notes here. 320 means the resolutions that are in a multiple of 320x200, while "Normal" means resolutions that are 4:3 (like 640x480). Correction stands for aspect ratio correction, and fake contrast is obvious.

---------------------------------------------------------------

4:3 setting___

320 = correction/fake contrast WRONG/CORRECT
Normal = correction/fake contrast CORRECT/WRONG


16:10 setting___

320 = correction/fake contrast CORRECT/WRONG
Normal = correction/fake contrast WRONG/WRONG

---------------------------------------------------------------

Using 16:10 with "Normal" resolution will make Doomguy's head even slimmer.

So, what I found is, PrBoom+ will do the aspect ratio correction, only if you choose the correct resolution to match it. For example, PrBoom+ will only correct the aspect ratio if you choose the right resolution to match the aspect ratio. Like 640x480 with 4:3, or 1280x800 with 16:10. If you choose a 4:3 resolution with a 16:10 aspect ratio, or vice versa, the aspect ratio will not be corrected.

This is not the same behavior that Chocolate Doom has in regards to aspect ratio correction. No matter what resolution I threw at Chocolate Doom, it corrected the aspect ratio, and also kept the correct fake contrast amount. I would really like to contact the maker of PrBoom+ and tell to use the same method of aspect ratio correction that Chocolate Doom uses, so it will be possible to play with the correct aspect ratio and correct fake contrast at the same time. Because right now, it is impossible.

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wesleyjohnson said:

The vanilla handling of the light levels and the conversion to the color map give a unique appearance.
This appearance may be familiar but is not really more correct than the display by other ports.


No way. PrBoom+ will render the fake contrast completely different depending on your settings.

wesleyjohnson said:

If you played for more than a few days, you would adapt to the new color and brightness appearance and the older vanilla appearance would look strange.


Yeah, but I don't want to play a port that cannot display the correct aspect ratio and/or fake contrast. I want the graphics (besides resolution) to be as close as possible to vanilla Doom.

wesleyjohnson said:

Most people would deny this, but it has been shown that the human vision system has a short memory for these kind of things.


Well if this is true, I provided pictures that show the difference between how these two source ports draw fake contrast, so you won't forget.

wesleyjohnson said:

Of more concern is the gamma setting, which determines the light curve, which ultimately determines how much detail you can see in the dark areas. The slightest adjustment of gamma overwhelms any of the little differences you are describing, and every player needs to adjust their gamma to match their monitor. Taking that into account, there is no possible correct appearance to chase after.


Since I made no adjustments to gamma in between these pictures, this is definitely not the problem. I can get PrBoom+ to draw the fake contrast just like Chocolate Doom does, but then the aspect ratio is wrong, and vice versa. Gamma has nothing to do with this, especially considering how PrBoom+ can indeed render the fake contrast correctly with the right settings. Just look at this picture. This is PrBoom+ rendering the fake contrast the way its supposed to be drawn, just to clarify no gamma settings are involved. I also have Chocolate Doom open below so you can see how its not correcting the aspect ratio (Doomguy's head is more square in PrBoom+, which shows no aspect ratio correction is taking place).



Now compare the above picture to this picture, and you will see how it draws the fake contrast wrong differently. Its very noticeable on the wall to the left. A section of the wall is supposed to be completely black on the left like it is in Chocolate Doom.

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shoober said:

This is PrBoom+ rendering the fake contrast the way its supposed to be drawn, just to clarify no gamma settings are involved. I also have Chocolate Doom open below so you can see how its not correcting the aspect ratio (Doomguy's head is more square in PrBoom+, which shows no aspect ratio correction is taking place).

Of course it's not. By stating that you want 16:10 resolution with 4:3 aspect ratio you're basically turning the aspect ratio correction off. Because it relies on your 16:10 image filling a 4:3 screen entirely. Just like good old times. Why your oldschool CRT display doesn't allow it (I'm assuming that the answer to my other question is also "yes") is anyone's guess.

The feature you're requesting is the ability to render 4:3 picture in 16:10 resolution with black borders. Although I can't guarantee that your precious fake contrast will work right this way. Try 4:3 resolution with 4:3 aspect ratio first.

shoober said:

So, what I found is, PrBoom+ will do the aspect ratio correction, only if you choose the correct resolution to match it.

Fine tuning is fine tuning. You have to know what you're doing and why.

shoober said:

I ment to say fake contrast, my bad.

No wonder I'm confused.

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Da Werecat said:

Of course it's not. By stating that you want 16:10 resolution with 4:3 aspect ratio you're basically turning the aspect ratio correction off. Because it relies on your 16:10 image filling a 4:3 screen entirely. Just like good old times. Why your oldschool CRT display doesn't allow it (I'm assuming that the answer to my other question is also "yes") is anyone's guess.


Any monitor can display black borders around an image. Its not dependant on the monitor, but the program. Certain things in the game, the like splash screen, intermission screen, and end scene were indeed rendered with black borders. Any monitor can draw black borders, its the program that has to support it. All monitors already support it.

Da Werecat said:

The feature you're requesting is the ability to render 4:3 picture in 16:10 resolution with black borders. Although I can't guarantee that your precious fake contrast will work right this way. Try 4:3 resolution with 4:3 aspect ratio first.


It doesn't have to have black borders, since Chocolate Doom can do this very same thing without black borders (render a 16:10 resolution with 4:3 aspect ratio correction) like I have mentioned before. If you actually read my posts, you would have already known what happends if I display a 4:3 resolution with 4:3 aspect ratio. Please refer to the table I posted above.

Da Werecat said:

Fine tuning is fine tuning. You have to know what you're doing and why.


No matter how much I fine tune PrBoom+, I can't get it to draw fake contrast correctly while having the aspect ratio corrected. Chocolate Doom can correct the aspect ratio, while drawing the fake contrast correctly, no matter what resolution it is, because Chocolate Doom has a different aspect ratio correction method like I've mentioned before.

Da Werecat said:

No wonder I'm confused.


Half of your confusion is not understanding the problem and not fully reading my posts (or understanding them). Since Doom's original resolution is 320x200, that means with PrBoom+, the only way the fake contrast will be drawn correctly, is if you use a resolution thats in the multiple of 320x200 with 4:3 aspect ratio. Do you even play Doom in software mode?

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