Shadow Mask Descriptions / Explanations / Information

[Napalmhardcore]

Hi,

While I'm new to the forum, I'm not new to MiSTer, so it didn't seem appropriate to post in the newcomers section.

I recently updated my MiSTer because I was interested in trying out the shadow masks. I acquired them via the update all script and there are quite a few options to choose from. It's been a long time since I used a CRT and while I can't remember the subtle nuances, I'm pretty sure I've never seen a CRT which looks like some of the examples I tried.

Presumably, different masks are attempting to emulate different displays or are made for specific use cases but I can't find any descriptions, explanations or much info in general.

Questions:
Are some masks better suited to outputting over HDMI while others are better suited to analogue output? Did shadow masks differ dependent on the size of the CRT? Are particular shadow masks best displayed at specific resolutions (720p, 1080p etc)? Are specific shadow masks best displayed on a large or small display (I have a 27" monitor for example. Should I be using the same mask as someone using a 55" TV)?

If the answer to some of the questions above are irrelevant, that's fine. It would be handy to have a brief explanation for the different masks though. At the very least it would be useful to know: 1) What display is being emulated. 2) What the intended use case is/why you should want to use a particular mask.

[Asteld]

Shadow masks are fairly limited, mostly due to limitations in output resolution. You should think of shadow masks as an effect to give your image/pixels a bit of 'character'. It follows then that really, you should just try out a couple of masks and stick to the one(s) you like.

It's not really about simulation ...although you can achieve results that approach the real thing.

On Mister, a shadow mask file defines how a single 'cell' of the mask should look. A cell that is defined with red, green, blue translates to a group of 3x1 pixels that filter red, green, and blue respectively. Mister then creates the complete shadow mask by simply repeating the pattern in the cell until the image output has been filled. There are 8 colours you can use and for each colour you can define the brightness of the 'on' state and its transparency in the 'off' state. Theoretically, you can create a very detailed cell by using lots of colour combinations. However, since each colour corresponds to a single pixel, the resulting cell will also take a lot of space on your screen. A single cell could therefore be very detailed and accurate, but the overall shadow mask may still look unrealistic due to the fact not as many cells can fit in the mask.

The above means that a shadow mask creator needs to balance detail, cell size and output resolution in order to get good results.

As a general rule of thumb, shadow masks can look more accurate, the higher your scaling factor is. The individual cells of the shadow mask will decrease in relative size as you increase your output resolution, hence you end up with more detail. This means that 1440p or 1536p (±6x scaling) is the best you are going to get on Mister.

Yes, some shadow masks are targeting specific (integer) scaling factors (e.g. 4x). Yes, some shadow masks apparently are better suited to analogue output. Whether it looks good ultimately depends on your specific setup, as well as simply your preference.

If you want accurate, your best bet is using a simple RGB stripe (eg. "Thin RGB") in conjunction with scanlines. On 1440p this looks absolutely fantastic and approaches the look on a PVM.

[Napalmhardcore]

Thanks Asteld. I'm using a 1080p display with 5x crop. Can you (or anyone else reading) suggest some masks that would work well for this resolution and scaling factor?

I've just had a more thorough search through the options available and to be honest, it's bit daunting. it's really not clear what the intended use case is for many of them as they don't give any clues as to what integer scale they're targetting. Many have confusing names and the names of some of them make it seem like people are just uploading any pattern they can think of. I appreciate options and I don't want to appear rude, but some of this seems like intentional bloat.

[DiamondDave]

Try different ones out, if you think it looks good, then that's the one you should use. There wouldn't be 100+ options if only one of them was "the correct" choice. You are overthinking this too much.

That said, the Trash Uncle Trinitron one is my favorite. You might not think so though, which goes back to my first statement.

[Asteld]

I agree with you in that there are perhaps too many choices currently. Eventually some curation is probably in order, but right now the shadow masks are still very much in the experimentation fase. In addition, there's just too many variables that affect the way a shadow mask looks. You can't just make a single mask that looks good for everyone. Some of these masks are going to look different based on the subpixel configuration of your display.

For a recommendation: start with some of the masks in the root folder. "Thin RGB" and "VGA" look very good in my opinion, although I don't know how they scale at 5x.

If you like those then you could also take a look in the "Jovec" folder, which contains masks that are essentially the same, but have a more pronounced definition (they are also darker). Those are the masks I created though, so obviously this is a biased recommendation.

[Napalmhardcore]

Try different ones out, if you think it looks good, then that's the one you should use. There wouldn't be 100+ options if only one of them was "the correct" choice. You are overthinking this too much.

The problem is that it's been a long time since I've gamed on a CRT, so my memory is pretty hazy. I don't know what looks "right" or convincing because I can't remember.

I'd like to have the closest experience I can get on the MiSTer to playing on a good CRT using my current monitor. If someone that owns a CRT has deliberately designed a mask which resembles the look of a particular display (a PVM/BVM/high end consumer TV) on a modern 1080p monitor with 5x crop, logically that's my best option to get the experience I want.

Because there aren't descriptions or explanation of what the masks available are, I don't know which one to choose to get the experience I want.

[DiamondDave]

The problem is that it's been a long time since I've gamed on a CRT, so my memory is pretty hazy. I don't know what looks "right" or convincing because I can't remember.

Then pick what currently looks "convincing" to you. If you enjoy it and think it looks good, that's the best one. That's the answer. How you remember something is going to be entirely different than from how someone else remembers something, so how can you expect to find a perfect match?

"I really like this vanilla ice cream I'm eating, but I'm not sure if it tastes like the the one I used to eat when I was a kid...then again, I can't really remember what that one tastes like anyways...can anyone tell me what it tasted like and if I should enjoy eating this one?"

[DiamondDave]

Also, there are several shadowmasks organized in folders for 5X crop and 1080p, and their titles contain the actual brand names of televisions they are intending to replicate or "PVM". It's not difficult to find something that suits your needs.

[Asteld]

Once the dust surrounding shadow masks on mister has settled, we can probably make a 'best of' selection. Certain masks at certain resolutions definitely mimic the look of real shadow masks. The UX with shadow masks is currently pretty bad, because, as you say, its very much trial and error. Unless you know how they work, you won't know what to look for. And even if you do know the masks only make sense if you look at the actual .txt file, which isn't possible through Mister itself.

For the record, the Jovec Masks are based on 'real' aperture grills, slot masks, and shadow masks. I've created them based on the reference images thread on this forum, as well as what I could find by searching around. The 'cells' at least, look pretty accurate. But again, the actual look and experience is going to depend on your specific setup. The unfortunate reality is that shadow masks are not one size fits all.

But again, a compilation of the best shadow masks for specific setups is definitely in order. All that's necessary is enough feedback and maybe some documented comparisons with real CRTs.

[Napalmhardcore]

Thanks again Asteld, you've been really helpful.

DiamondDave, you've been less helpful. What's with the attitude? I came here looking for information not only for myself, but knowing that most Google searches on this topic lead here, it will help others. Yes, a handful of them have self explanatory names but the majority of them don't and it's confusing for people that are new to this particular topic.

Also, your ice cream analogy/insult isn't apt. People often claim that playing on a good CRT is a great experience and people have said that using a shadow mask does a reasonably good job of recreating that. I want to know I'm using a mask that's appropriate for my setup so I know I'm getting a similar experience to the people who are claiming it's a great experience so I can judge it for myself. It's not about recreating what I do or don't remember.

[DiamondDave]

There are multiple shadow mask threads on this forum already, with several members giving their (varying) opinions on which one looks the best. Try some of those options.

I already told you the Trash Uncle Trinitron one is the best (imo), so you should either try that and believe it, or realize that it's all personal preference and stop agonizing over it.

[FoxbatStargazer]

I haven't had the opportunity to look at a ton of CRTs lately, but what I can say, is that for the 27"+ consumer Sony WEGAs and 19" 1200p VGA monitors, even 6x isn't really fine enough to replicate masks on the proper scale. On the aperture grille of a 32 WEGA, it seems like a single SNES pixel breaks down into 6-8 lines of light, never mind trying to subdivide those into RGB. And I can't even see a discernable pattern on the 1200p VGA monitors up close, to compare to the really large patterns on the base VGA shadow mask.

Only the few experimenting with subpixels can really get the scale right to mimic some of these "better" large displays, but that approach comes with its own limitations. I think this is part of why there is simple stuff like RCYB stripe, its not meant to mimic exactly any kind of CRT, just add a bit of texture in some color fringing that remind you of the real thing, without trying to replicate it 1:1. So I recommend not getting caught up in "accurate" unless what you want to replicate is some low TVL stuff, we don't really have sufficient resolution to do much better.

[LamerDeluxe]

I agree. Don't go for accurate, it is not possible on a TFT display. Go for a pattern that gives a good enough impression or that pleasantly breaks up blocky pixels, as well as not interfering with scan-lines, if you use them.

My sub-pixel patterns are pretty tiny, still not as tiny as the real thing and less visible on a small display. And they only work on displays with horizontal RGB-ordered sub-pixels, at native resolution.

Patterns that look good on one core might not look good on another, or on all resolutions of a core.