Scaling artifact in 1080p

[mahen]

Howdy there !

I recently had to change my monitor and got a pretty expensive 1080p Iiyama monitor.

I mainly use the Minimig core. I quickly had the feeling something was wrong with scrollings -- it was not as smooth as with my former cheaper monitor. I had the feeling some lines were inconsistently displayed, stuff was disappearing when scrolling.

THEN I NOTICED THIS : have a look at this screen shot (high res PAL mode).

SCREENSHOT :

IMG-20201208-130258.jpg (5.69 MiB) Viewed 2838 times

The letters are completely inconsistent.
Despite my using a standard 1080p mode, as my monitor is 1080p. Despite using integer scaling. Even when trying the compatible vsync setting.

What is happening ? How the hell can the letters be distorted ?

NOTE : THIS IS ESPECIALLY VISIBLE WHEN USING (as on the pic here) NO SCANLINE FILTER / NO FX. -- but it's still visible with them.

Please help, I'm gonna throw my MiSTer out of the window !
(and yes, I tried all settings combos on both the screen & MiSTer)

[mahen]

I double checked on my projector : same scaling artifacts on the WB. Scrollings look better though...

[SuperBabyHix]

Someone please correct me if I am wrong, but the integer scaling mode is only for the vertical axis. The horizontal will not be perfectly even because most retro computers and consoles did not have perfectly square pixels, especially when scaling to the correct aspect ratio.

It would be especially noticeable on the Amiga workbench since, by default, it uses a screen mode of ~720x288. Try using a filter like Gaussian sharp NN, which will apply interpolation only to the X axis. That should help maximize sharpness while helping to mitigate scaling artifacts.

[mahen]

Hmm, so it means the strange scrolling is unrelated and due to the screen :/ some lines seem to "dance" when there is a scrolling and nope it's not tearing.

And this is a 40-160 Hz iiyama monitor

[SuperBabyHix]

Just so I make sure I understand what you are seeing correctly, the pixels are uneven. basically not all the same size? For example, in your image, the letter m. The "legs" of the letter are not all the same width. Is this what you are talking about? And it is especially noticeable when things are scrolling?

[mahen]

I think there are 2 différent issues after all.

The distorted characters (visible on my both screens in hires) shows that the same letter is displayed differently depending on where it is on the screen.

The scrolling issue happens only with my new gaming LCD in low res. It gives the unpleasant feeling the image changes when it is moving. Like partly disappearing lines or overlapping éléments (in some specific areas). Ew ! First time I see that !

[SuperBabyHix]

Ok, so that isn't an issue with your monitor, it is because the Amiga (and most everything else as well) has non square pixels. Try using some of the filters (https://github.com/MiSTer-devel/Filters_MiSTer) to see if they alleviate the problem for you. I would start with Interpolation Sharp and go from there. You may even find that with the filters you can disable integer scaling and still get a nice image while filling more of the screen.

Also, the vsync setting wont affect this, so if your monitor works with the low lag setting then go with that.

[Chris23235]

What resolution is used in the WB?
As far as I see it integer scaling should solve the problem, because for example it displays a 640*480 resolution in 1280*960 so that every pixel of the original system occupies 4 pixels on your full HD display. This works for me, I only have distorted letters when I don't use integer scaling.
Can you post the Mister.ini settings for your Minimig core?

Ignore the above, I forgot, that this is about the Minimig core. In Minimig you can adjust the screen size (under the video setting) this is to make the picture fill the screen better because of the many different resolutions the Amiga uses. The setting is saved in the core per resolution so the next time the core will use your settings. This is what the picture looks like, when I quickly adjusted the size manually (PAL Hi-Res):

iV8TMSo.jpg (1.44 MiB) Viewed 5086 times

I am sure with a little more effort I would have been able to get it better. Ignore the white glow around the letters, this is because I display the picture on my Full HD TV in 720p with 50Hz because the core doesn't sync when in 1080p 50Hz, the glow goes away once I process the picture with one of the filters, but for the sake of clarity I didn't do this this time.

[mahen]

HI, thanks for your reply. Yep indeed I find it pretty tough to use the "adjust display" option !

Regarding my issues...

1) about the irregular letters : can any of you guys confirm you do have the same result as me, under the WB, when disabling all filters / FX ? (type several times the same letter in a terminal for instance and check if they look inconsistent or not)


2) about the scrolling issues, I guess my new (sigh) LCD monitor applies some kind of weird post-treatment. I'll have to get another one. Any suggestion regarding a monitor giving the smoothest possible scrollings with the Minimig core ? This Red Eagle 160 Hz Iiyama for some reason is the worst I've got so far.

[SuperBabyHix]

Mahen, Yes, if you disable all filters you will have uneven pixel scaling even if you have vscale=1 in the mister.ini. That only applies integer scaling to the vertical axis, hence Vscale. Loot at the picture Chris23235 posted. Notice the checkerboard pattern is very uneven.

This is not a bug, this is just the nature of scaling. The Amiga Workbench HiRes Pal screen mode is 720x288. So let's say you want to scale that up to 1080p with vscale=1 (integer scaling on the vertical axis.) 288 x 4 = 1152, too big for 1080 so we have to go with 288 x 3 = 864. So 864 vertical lines fits nicely into 1080 with a bit of a border. So now we multiply the horizontal, 720 x 3 = 2160. That's too big to fit into our 1920 horizontal resolution. But, double whammy, we aren't scaling it to 1920, we are scaling it to 1440 because the proper aspect ratio of the Amiga screen was 4:3. 1440x1080 is the 4:3 resolution at 1080p. So cramming 2160 into 1440 means that the pixels are going to be unevenly sized if we don't use a filter to even it out.
(these numbers may not be 100% accurate, but the gist of it is still the same)

This is much less noticeable when playing Amiga game, or games on other system and computers because they typically don't employ a high horizontal resolution. Usually something closer to 360x288, 320x240, 256x224, etc... Workbench and WB applications though make it very apparent.

Also, I don't think any of the ScaleFX filters like HQ2x will help because I believe those are applied to the image before the scaler ( I believe those are a holdover from the MiST when we were limited to the scandoubler.)

For the scrolling issue, is it judder? Is it that the scrolling is not smooth, or that the things that are scrolling change is size as they move?

[mahen]

Thank you so much, I've been mistaken for quite a long time -- I always thought integer scaling applied to both vertical & horizontal axis.

Regarding the scrolling issues. This is not a lack of smoothness -- which is more or less noticeable depending in the game or screen. It's that, the picture really seem to be different when moving. As if some elements of the picture were altered temporarily. It's especially strange in the 4th table of Slam Tilt where it give the impression some elements of the table (which are theorically fixed) are moving the one above the other and vibrating. Weird !!

I'm really looking for the "perfect monitor (not TV)" for the Amiga core suggestion -- esp. regarding smoothness / clarity

[SuperBabyHix]

That weird movement is because of the uneven scaling. Some people call it shimmering. There is nothing wrong with your monitor. If anything, it may be more noticeable on your new monitor because it might have less motion blur than your older monitor. Try some of the filters (https://github.com/MiSTer-devel/Filters_MiSTer).

[mahen]

HI ! Nope actually it's something else, I do have integer scaling enabled ! I'm used to seeing "shimmering" on other monitors with uneven scaling. This is different.

Too bad I cannot show you...

[SuperBabyHix]

Is Slam Tilt using an interlaced mode? Try setting your Workbench to Pal HiRes Laced and see if it has the same effect.

[mahen]

I'm not sure, I can test a bit later. But FYI even simple vertical scrollings in console cores in 60 Hz (i.e. The Addam's Family / Genesis) are little weird -- as if lines were partially disappearing. It's as if there were tons of remanence while this is a 1 ms screen. And yep : integer scaling enabled !

[SuperBabyHix]

I did have a thought, does your new monitor have an overdrive feature? If so, try adjusting that. I know on my monitor if it is set too high it does cause some weird issues.

If not, maybe post your mister.ini.

[mahen]

Yep, I tried overdrive setting, from -2 to +2... It does not seem to improve the situation.
There is massive ghosting with the +1/+2 values. (visible when dragging a screen for instance)
I really tend to think this monitor was not meant for this use case. But to such an extent this is surprising.
I'll post my mist.ini ASAP.

Also I'm gonna test this screen with RetroArch and check if I get the same phenomenon.

Thanks for your help

[rsn8887]

I think this is a repeat, but might be good to check some or all of these things, if you haven't done so.

First: Make sure you actually use 1080p output by setting video_mode=8 in mister.ini. The default is video_mode=0 which forces output to only 720p, which looks horrible on a 1920x1080 screen, because your screen firmware will do crappy scaling to 1080p.

Second: For low lag and perfectly smooth scrolling, use vsync_adjust=2 in mister.ini. This will cause the output refresh rate to change to 50Hz, 49 Hz, 58 Hz etc depending on exact refresh rates of the cores.

Third: I recommend setting filter to "Normal Upscaling/bilinearsharp_07" or "interpolation_sharp". It will fix any remaining issues with pixel shimmer. If you don't use a filter, the Amiga picture via HDMI will always look horrible. The filter makes sure you get accurate pixel shapes with minimal blur and no shimmer. See also here: https://gamingprojects.wordpress.com/2017/12/ , for an explanation of the effect from your screenshot. Integer scaling doesn't help you, because almost all machines had rectangular pixels, as was mentioned before.

Fourth: Don't choose your update speed on your monitor too fast. Many gaming monitors start to display ghosting and flickering when high contrast images move quickly and the update speed is set too fast. Remember a frame is about 16 ms or so on most machines, so no need to set the screen to 1ms. You can test this with the Windows 10 mouse pointer motion too. You will see flickering and ghosting mouse pointer in motion if your screen update is set too fast. This can be set in the menu of your screen. My LG monitor has settings like "Very Fast, Fast, Normal..." etc. and I don't use "Very Fast" because it causes ghosting and flickering with fast moving images.

[mahen]

Hi ! Thanks a lot for your long reply -- I had already checked all of those May be useful for other people, maybe we should add your post to the wiki !