How much can you scale up 4K for a 1080p project?

[Sean]

If you're working from 4K files, but you're finishing at 1080p, I'm wondering what percentage you should be able to scale up/zoom-in on a 4K image before you have noticeable loss of resolution. I would think that at 1080p, you're "throwing away" a certain amount of resolution when finishing at 1080 anyhow. Any suggestions? I don't think it's as simple as 1080p is about 200% (math!?) bigger than 4K, so you should be able to zoom in 200%. Or is it?

[Michael Hastings]

If you're working from 4K files, but you're finishing at 1080p, I'm wondering what percentage you should be able to scale up/zoom-in on a 4K image before you have noticeable loss of resolution. I would think that at 1080p, you're "throwing away" a certain amount of resolution when finishing at 1080 anyhow. Any suggestions? I don't think it's as simple as 1080p is about 200% (math!?) bigger than 4K, so you should be able to zoom in 200%. Or is it?

4k is about 4 times as big as 1080p so you should be able to do 400% or a little more.

[amrrahmy]

u need to account the 1.5 factor,
the actual image recorded on 4k is about 3k give or take, so it's usually considered a 2k workflow and not 4k.

it depends on ur aspect ratio, but u need to keep in mind that u can't cut 1080 from 4k directly, the image would be too soft, it needs to be 3k or 2k to get the best quality possible and then u can cut from it however u see fit

down-converting the image from 4k to 2k or 1080 should not make a big difference in quality when viewed in 1080.

the new red epic has a full frame sensor, in which case cutting from the image directly would be available.

[Tom Lowe]

You probably want to downsample the image at least 20% or 30% to keep the image super clean. Pixel-for-pixel 100% crops will reduce the quality of your image, especially if the lighting is only mediocre.

[amrrahmy]

u dont need to change the image first and then cut it, but u need to account that the image needs both processes to get the best results.

[amrrahmy]

You probably want to downsample the image at least 20% or 30% to keep the image super clean. Pixel-for-pixel 100% crops will reduce the quality of your image, especially if the lighting is only mediocre.

yes, something close to 33.3% give or take, so 3k in 16:9 is perfect quality

[Tom Lowe]

yes, something close to 33.3% give or take, so 3k in 16:9 is perfect quality

yeah, that's a good rule of thumb.

[Sean]

I should have given a couple more details: I'm not cropping...although maybe the end-result of scaling up amounts to the same thing? I'm actually scaling the 4K file itself (in After Effects). So I'm starting with a 4K image and then after I scale the size up (i.e., "zoom in"), I then downconvert the finished comp to 1080. But sounds like 33.3% is the rule of thumb. Thank you!

[amrrahmy]

if u want to take a portion of the 3k file, don't zoom in then scale down, just crop to the right amount of the image. for best quality results.