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How does movie and image scaling work? How would a monitor with a funky resolution be for movies? This is the thread for you.

So don't kill me if this is the wrong section to post this or if it is a repost, I haven't found anything like this on the forum but maybe I'm trippin'.

 

What is the point of this thread? Simply, I feel like there is a bit of confusion related to how image and movie scaling works on monitors with non-standard resolutions, such as 21:9 2560x1080 or the rumored iphone 6's 1704x960 screen. Since I have not found a thread on this forum that treats this argument I decided to make it myself. Now, if I say anything wrong or stupid (entirely possible) please let me know so I can edit this post and make it as informative as I want it to be.

 

 

When you play a movie, that movie file has a fixed resolution. Now, if you play that movie on a screen that has a resolution higher than that movie's resolution (in fullscreen of course), the image gets stretched. If the new resolution is not a perfect square multiple of the original resolution (4x, 9x, 16x...) the process of stretching the image generates artifacts or degrades the overall visual quality, as a non-integer amount of physical pixels is assigned to each pixel in the video. While on a 4k monitor each pixel of a 1080p movie would get exactly 4 physical pixels that show the same colour, a 1440p monitor (for example) will have to decide which virtual pixels get more real pixels than the others and which get fewer.

 

post-42239-0-53776700-1401543523.gif

Hopefully this image makes the difference clearer. Therefore watching a 1080p movie on a 1440p monitor actually degrades the experience compared to a native 1080p panel (counter-intuitive isn't it?). There are algorithms that monitors use to make this effect less noticeable (such as "advanced scaling" shown in the image above), but they cannot solve it completely.
A very similar problem can be experienced in reverse, where a screen is used to play a movie which does not have a perfect square multiple resolution of that screen (for example playing a 1080p movie on a 1704x960 iphone). In this case the issue is caused by the opposite process: instead of having an integer square number of the movie's pixels assigned to each physical pixel, you have 1.27. The phone will therefore have to choose what it can display and what it can't on the fly, causing artifacting similar to what we have in "advanced scaling".
 
3840x2160 is the only common (or semi-common) resolution which does not suffer from scaling when watching both a 1080p movie or a 720p one. In fact it is exactly 4 times 1080p and 9 times 720p.
[update]
Apparently, even at 4k the video player will use an interpolation algorythm. Thanks to the above fact however it impacts quality much less than interpolation on an odd resolution would and possibly actually increases the quality like AA would in a video game.
[/update]
 
Common "non standard" resolutions that would be affected by this problem with 1080p movies (feel free to ask me to add yours if it doesn't figure here):
21:9 - 2560x1080*, 3440x1474, 3440x1440(not quite 21:9)
16:9 - 1704x960, 1280x720, 1366x786, 1024x576, 853x480, 2560x1440, 1600x900
16:10 - 1280x800, 1536x960, 1680x1050, 2560x1600
4:3 - 800x600, 1024x768, 1280x960, 1600x1200
 
*(only if you eliminate the black bands you get in some movies)
 
Common resolutions for which no degenerative scaling occurs (for 1080p movies):
21:9 - 1920x823*, 3840x1646
16:9 - 1920x1080 (DUH), 960x540, 640x360 (resolution of my current phone ^^), 3840x2160
16:10 - 1920x1200, 960x600, 640x400, 3840x2400 (who even has this?)
4:3 - 1920x1440, 960x720, 640x480, 3840x2880 (weeeeee!)
 
 
Next time you are interested in purchasing a monitor with a "funky" resolution, bear this post in mind. If you watch a lot of movies on your monitor, be aware that resolutions which suffer from scaling are not ideal. I hope this is useful for someone.

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Very nice thread. Please make the text dark theme compatible though.

I'm not sure how to, can you explain me please?

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I'm not sure how to, can you explain me please?

In the text colour menu (Next to font size and typeface) click Automatic.

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movies unlike games arent affected as much because if you zoom is a lot u wont see separate pixels they blur into each other

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movies unlike games arent affected as much because if you zoom is a lot u wont see separate pixels they blur into each other

This is a misconception: even though movies do have blurry images, pixels are still a fixed number (each pixel has one colour only, regrdless of surrounding pixels) and therefore scaling will affect image quality just as much (in fact the blur effect could become irregular as a result of some colours getting more pixels than others). What you get is similar to a badly compressed video, with irregular areas being the same colour. It might not be as noticeable as a game because the image is blurry regardless and your brain does a lot of the job, but it is still a loss in quality and many people will notice it. Of course it is not terrible or unacceptable, but it is present and if you watch a lot of movies on your monitor it can get annoying.

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  • 1 month later...

What really matters is the aspect ratio here, not pixel counts.

 

Also, you linked this in another thread about how the iPhone has issues with scaling, first of all, that's not a documented issue, and I'd like to say that it doesn't and I've never had any issues with it. It's just a standard 16:10 aspect ratio. 

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Cool. Although 720p (and 1080p) look fantastic on my netbook, since it's basically a really scaled down 1920x1200 screen.

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What really matters is the aspect ratio here, not pixel counts.

Also, you linked this in another thread about how the iPhone has issues with scaling, first of all, that's not a documented issue, and I'd like to say that it doesn't and I've never had any issues with it. It's just a standard 16:10 aspect ratio.

Scaling is not subjective. It's happening no matter what and depends on resolution, not aspect ratio. Wether you notice it or not, that's another matter entirely. In the op I explain exactly how it happens and why it COULD be an issue to the keen eye. The smaller the screen, the less noticeable it is, but if you think you're getting the same exact quality you would with a native 1080p screen, you're deluding yourself. Furthermore, 16:9 movies don't suffer from scaling on different aspect ratios in more than a few cases, for example 1920x1200.

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Scaling is not subjective. It's happening no matter what and depends on resolution, not aspect ratio. Wether you notice it or not, that's another matter entirely. In the op I explain exactly how it happens and why it COULD be an issue to the keen eye. The smaller the screen, the less noticeable it is, but if you think you're getting the same exact quality you would with a native 1080p screen, you're deluding yourself. Furthermore, 16:9 movies don't suffer from scaling on different aspect ratios in more than a few cases, for example 1920x1200.

Whoa there, cool down.

 

I didn't say it was subjective, just that I've never noticed it. And for what it's worth, the iPhone has the same aspect ratio as a 1600*1200 screen, so therefore it won't suffer from scaling issues. I also realize that a 1080p screen would deliver a most likely better experience, however I vastly prefer 16:10 for coding and most other ordinary tasks.

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Very nice thread. Please make the text dark theme compatible though.

Ch-ch-check out this script for greasemonkey (or whatever your browser uses) from colonel_mortis.

 

http://linustechtips.com/main/topic/140478-features-suggestions/page-27#entry2446662

 

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  • 6 months later...

 

 
3840x2160 is the only common (or semi-common) resolution which does not suffer from scaling when watching both a 1080p movie or a 720p one. In fact it is exactly 4 times 1080p and 9 times 720p.
 

 

 

if you think  a 3840x2160 will just show each pixel of a 1920x1080 movie exactly 4 times.

that is a wish, but actually not true at all. 

there are some scalers which can do that, but the majority you would find in displays uses some sort of interpolation even for even divisions/multiplications.

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if you think  a 3840x2160 will just show each pixel of a 1920x1080 movie exactly 4 times.

that is a wish, but actually not true at all. 

there are some scalers which can do that, but the majority you would find in displays uses some sort of interpolation even for even divisions/multiplications.

 

That is if you set the resolution to 1080p. However if you play a 1080p movie with, say, vlc on a monitor that is set to 2160p (native), the player will take care of scaling and you'll get an almost perfect 4 to 1 ratio.

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That is if you set the resolution to 1080p. However if you play a 1080p movie with, say, vlc on a monitor that is set to 2160p (native), the player will take care of scaling and you'll get an almost perfect 4 to 1 ratio.

 

pretty sure the standard scaler in vlc is bicubic

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pretty sure the standard scaler in vlc is bicubic

 

Wouldn't the bicubic scaler automatically end up scaling it perfectly?

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Wouldn't the bicubic scaler automatically end up scaling it perfectly?

 

nope.

here a bicubic scale from photoshop (8x8 to 16x16)

 

WioAaog.png

 

I am NOT saying that 1080p looks bad on a 4K screen.

I am just saying, that scalers don't work that way you would think.

 

edit:

UZlCe4k.png

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-.

 

huh. At least I'm not wrong in saying it won't look as bad as scaling 1080p to a non-multiple resolution... do you know any vlc scaler add-on that can do perfect scaling?

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huh. At least I'm not wrong in saying it won't look as bad as scaling 1080p to a non-multiple resolution... do you know any vlc scaler add-on that can do perfect scaling?

 

I highly doubt it, but honestly it isn't really a big issue.

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I was considering an LG34UC97 which has 3440x1400 resolution (21/9)
Reviews said it was amazing for movies/series (especially if they can be found in 21/3) but I was wondering, since I read this topic :
Won't it be "ruined" with this scaling problem, since most of the content out there is still for full hd resolution?

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I was considering an LG34UC97 which has 3440x1400 resolution (21/9)

Reviews said it was amazing for movies/series (especially if they can be found in 21/3) but I was wondering, since I read this topic :

Won't it be "ruined" with this scaling problem, since most of the content out there is still for full hd resolution?

 

That's what I always say when people recommend 21:9 monitors for watching movies, everyone seems to conveniently forget this. You will get a lot of interpolation, and considering you'll probably sit close to your monitor you'll notice it pretty well, too. I'm not saying 21:9 monitors never make sense, but recommending them for movies seems a bit of a stretch to me.

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With 4K, if it is the same size it will look the same, if the movie is 1080P if it is 4K it will be the same, if it is divisible by 4 exactly it will be fine

 

As discussed in this thread, that is not really how it works

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That's what I always say when people recommend 21:9 monitors for watching movies, everyone seems to conveniently forget this. You will get a lot of interpolation, and considering you'll probably sit close to your monitor you'll notice it pretty well, too. I'm not saying 21:9 monitors never make sense, but recommending them for movies seems a bit of a stretch to me.

 

The experience is just so much better, interpolation or not. I lack a 21:9 on my home PC, but would kill for one if I didn't have more productive things to spend the money on.

 

Also, most BluRay rips are a weird resolution, like 925p or something. Might be 823, but I don't think so.

EDIT: Is apparently 1920*800. Not sure how well that scales but it looks pretty sweet on a 2560*1080 display.

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The experience is just so much better, interpolation or not. I lack a 21:9 on my home PC, but would kill for one if I didn't have more productive things to spend the money on.

 

Also, most BluRay rips are a weird resolution, like 925p or something. Might be 823, but I don't think so.

EDIT: Is apparently 1920*800. Not sure how well that scales but it looks pretty sweet on a 2560*1080 display.

 

Excuse me, but what are your sources for saying it looks so much better if you don't have one?

 

Blu-rays in the 21:9 format have a 1920x800 resolution, because they had to fit 21:9 in 1080p. Therefore it will get stretched to fill 2560x1080. Of course the further you sit from the monitor the less you will notice, but at that point why even bother with a 21:9 when you could get a larger 1080p instead?

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Excuse me, but what are your sources for saying it looks so much better if you don't have one

Have three 2560x1080 at work. Unfortunately can't spend my limited time in the office watching movies. Had one at home, before deciding I needed it more for productivity. Have had hands on experience with both LGs and AOCs 3440*1440.

It looks better to me, at about 2 feet of distance. Whereas a 1080p at 27" at that distance kinda screws me over in general desktop use. I'm sure there is stretching and interpolation going on on the 2560*1080s but to me that's a) completely unnoticeable and b) much more preferable to black bars.

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