Author Topic: Does anyone know anything about "fixed-grid" resolution of TVs?  (Read 259 times)

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Offline mr_lou

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Very early into the betatest phase of 8-bit Memoirs, I discover a very annoying issue.

My videos look very different on different TV's.

Vertical lines appear. Vague on some TVs, and very visible on others.

So far I've found out that these lines appear because either the TV or the Blu-ray player scales the image. There's a setting on the player where I can set "Resolution" to "Auto" or "Original". If I set it to original, the vertical lines are gone - but now the image can't fit on the TV Edges are cut off.

After some googling I've learned that LCD (and others) TVs had a socalled "fixed-grid resolution". But I can't figure out what this typically is. Is there any standard "fixed-grid resolution" on TVs? What terms do I need to search for in order to find this info?

Thanks
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Offline Bryce

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The native "fixed grid resolution" of an LCD/TFT is the highest resolution that it works at. So a 800x600 LCD has 800x800 pixels. On CRTs it's a bit more complicated. Most early TVs had a fixed grid that could just cover PAL or NTSC pictures, so the grid will be approx. 360x300, but that depends completely on the TV and CRT manufacturer. Later TVs had a much finer grid to supposedly improve the picture quality.
The problem is that CRTs were designed to display analogue signals which have a defined number of rows, but not a really a fixed number of horizontal pixels. To find out exactly what resolution the grid has, you would need to find out the part number of the CRT and try to find its datasheet, but I doubt you will find these.

Bryce.

Offline mr_lou

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This is for LCD TVs.

The videos for 8-bit Memoirs are all 1280x720 pixels.

I can setup the blu-ray player to output resolution "Auto" or "Original".

Likewise, the TV itself can also be setup to have a resolution of "Normal" / "Original" or "Scanning" or sometimes "+1".

So both the player and the TV has scaling options.


If I set the blu-ray player to "Original" (sometimes also called Direct Source), and the TV to "Normal", then the 1280x720 pixels can't fit on the screen. The image is too big.

On my own Sony blu-ray player and Sony TV, it looks like it's cutting off about 20 pixels in each side. I.e. 40 pixels horizontally and vertically. (On other systems it varies a bit. But it's about 20-30 pixels that is being cut off I think).

So this would make the fixed-grid resolution 1240x680 ? Makes no sense. I don't get it.


Anyway, the problem with it all, is that my emulation of a CRT screen creates a pattern of dots on the video. Looks great when the video is displays 1:1 - but when the image is scaled (which seems to be the case), then it doesn't look that good. So I'm wondering how to fix this.
So far I'm getting the best result if I set the player to "Original", and the TV to "Scanning" or "+1" (depending on brand and model). In other words, it seems that nowadays it is the TVs that has the best scaling algorithms.
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Offline Bryce

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What's the model of the LCD TV that's cutting the sides off?

Bryce.

Offline gerald

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On my own Sony blu-ray player and Sony TV, it looks like it's cutting off about 20 pixels in each side. I.e. 40 pixels horizontally and vertically. (On other systems it varies a bit. But it's about 20-30 pixels that is being cut off I think).

So this would make the fixed-grid resolution 1240x680 ? Makes no sense. I don't get it.
That's what I would call a side effect of TV maker to have something similar to CRT.
On CRT, the video signal was slightly oversanned to make sure you do not see any of the technical area (sync, teletex ....)
On LCD they do this overscan by default even if it's not needed anymore (even my desktop monitor did it on HDMI input).

Offline Sykobee (Briggsy)

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Most older LCDs are 1366x768 (yes, seriously, so not a 1:1 match to 1280x720). HD Ready.
Better LCDs are 1920x1080 - Full HD. TBH I'd be making your videos in this resolution these days.
Then there are 4K TVs at 3840x2160, which should not have any visible issues.


That's the native resolution - all the scaling that is done is going to affect the signal before it gets to it, and many TVs also overscan an incoming HDMI signal as well (some have the option to turn it off, or "PC Mode"). It could be the BluRay player is upscaling to 1080p, then the TV is stretching that again.
« Last Edit: 13:53, 07 September 17 by Sykobee (Briggsy) »

Offline mr_lou

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What's the model of the LCD TV that's cutting the sides off?

Well my own old Sony is a KDL-40W5500, but I'm seeing the behavior on all TV's I've tried so far.

That's what I would call a side effect of TV maker to have something similar to CRT.
On CRT, the video signal was slightly oversanned to make sure you do not see any of the technical area (sync, teletex ....)
On LCD they do this overscan by default even if it's not needed anymore (even my desktop monitor did it on HDMI input).

Yes, I've heard that around a few times now. But basically that would mean that the image would be too big if it was set to "Overscan". This is not the case.
The case is, that the image is too big when the setting is set to "Original" or "Direct Source" - on both TV and player.
In order to "scale down" the image to fit the TV, I will have to set it to "Auto" on the player OR "Scanning" on the TV.
Setting both to "Original" makes the image too big. So to me that doesn't qualify as "Overscan".
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Offline mr_lou

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Yes, I've heard that around a few times now. But basically that would mean that the image would be too big if it was set to "Overscan". This is not the case.
The case is, that the image is too big when the setting is set to "Original" or "Direct Source" - on both TV and player.
In order to "scale down" the image to fit the TV, I will have to set it to "Auto" on the player OR "Scanning" on the TV.
Setting both to "Original" makes the image too big. So to me that doesn't qualify as "Overscan".

Ok, I have gotten an explanation for this on another forum.

As you say, in the good old days CRT TV's magnified the image a bit to hide technical areas in the edges and so.

LCD TV manufacturers still do this, though there's absolutely no need. It is very silly.

What's even more silly is that "Original" or "Normal" setting = Overscan.
So if you want "real normal", you actually have to zoom out.
This is why on my Sony Bravia TV I have to choose "+1" in order to get a correct picture, instead of "Normal".
Talk about an illogical mess.

Now I have to try to explain this to my users somehow....... otherwise they won't get a full picture when viewing 8-bit Memoirs....

It really is a mess because: If the Blu-ray player is set to Auto, then it will detect the screen resolution from the TV. But the TV will send back a smaller resolution that it's able to display because of the overscan setting, to which the Blu-ray player then will say: "Ok, then I'll just go ahead and scale the image before sending it to the TV".
Obviously we don't want that, but that's the default setting of most setups. You probably have it set up like that yourself at home.
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