Why do videos look extremely pixelated on small screens?

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Sometimes I will want to send a video to a friend through text messaging. So the phone has to shrink the video down in size. But it looks so pixelated and I don't understand why. A DVD in SD on a regular size TV screen will look fine. But a 4K video that's been shrunk down, but on a much smaller phone screen playing, looks super pixelated, when the screen is much smaller. Why is that?

CONSIDERATIONS WHEN ENLARGING IMAGES: DPI, PIXELATION, AND RESOLUTION

Hopefully the above article will help you understand

I think you're mistaken. Videos do not look pixelated on smaller screens; the complete opposite is true given a fixed resolution. What you're likely seeing is downscaling and compression artifacts introduced by whichever program or service you're using to send video in an attempt to reduce the size of file transfers.

the smaller the display, the fewer the number of pixels which will fit in it, hence the coarser image.

Oh okay, but there images where they are small but still looks great. For example, if I watch a video on youtube on my phone, it can look great and not pixelated at all, and it's still the same size of the phone screen. So I didn't think that the size of the screen mattered therefore.

there are psychovisual factors involved in reducing an image or displaying images in general on tiny screens, that good designers take into account. there is generally some algorithmic processing going on behind the scenes of the better small displays.

Those two combined.

When you watch a low resolution video on a small screen it's already been scaled down as best as possible. When you watch a higher resolution video on a small screen that scaling needs to be done in real time, so it's lower quality in order to occur without latency. The lower quality results in the artifacts/blocky low contrast areas, etc.

Well what I don't understand is, the video I sent is 410p, after it arrives in it's scaled down form. My DVD player can make a 480p DVD look good on a bigger screen TV. Yet the much smaller phone makes 410p look pixelated. How can so much pixelation occur on a small screen if if there is only a 70 pixel different between 480 and 410, if that makes sense?

when you have a different ratio of pixels you are translating higher -def video to, you have to do something called pixel mapping which means you do psychovisual tricks to the video stream that tricks your eyes into not seeing the resultant distorted image.

Because it's no longer 4K when you send it. There is a new term you should learn. It's called DOWNSCALING.

When you send the video from your phone, the original file is too large to send through text message. So, the software automatically DOWNSCALES the original files to a smaller and crappier version that can be sent through without crashing your friend's phone. Nothing to do with the size of the screen. The texting software deliberately takes a high-quality video and makes it crappier....because crappier takes up less space and is easier to send.

Summary: A downscaled video looks crappier, but takes up much less space on your friend's phone. This is a default feature of most phones. Better quality = larger file size = harder to send. **Kind of like when a newspaper photo looks like black-and-white crap. It's easier and cheaper to print it that way than it is to reproduce the original high-quality color photo.

Say it with me: DOWNSCALING.

Last edited by ezbzbfcg2 on 06 Jan 2021, 3:46 am, edited 1 time in total.

Quality is a matter of more than just resolution. A DVD is compressed with a less lossy codec than a file being sent in the manner ezbzbfcg2 describes. It's not just 410 vs. 480, it's also how they're compressed.

By definition, DOWNSCALING causes the lossyness deliberately to make the file easier to send. The information is "lost" in the sending process, hence the poorer quality.

Is that why old YouTube often looks like crap?

what is worse is what Utube does with audio, it decimates it.

I thought it was both. Youtube may downscale (and even gives the option of selecting between different video qualities. You can choose to downscale an otherwise high-quality video).

But most older youtube videoes were recorded in that gray area. Post-analogue, pre-HD digital. So, they're digital, but a naturally lower-quality digital.

Same reason TV shows from the 70s have that dingy quality to them, even though they're in color.

I still have my first digital camera from 15 years ago. It'll shoot digital videos, yes. But they're a far cry from anything HD.

Last edited by ezbzbfcg2 on 06 Jan 2021, 4:04 am, edited 1 time in total.

That's the real atrocity of Youtube. Yeah, it often sounds better than a fuzzy recording off the radio onto a cassette tape, but it's nowhere near the audio quality it could be, even with compression added.