C300: 1DC 4K vs C300 1080p…resolution issue

[Nicholas Natteau]

I thought I understood the difference between 4K and 1080p, but now I'm confused all over again.

If 1080p resolution is 1920 x 1080 = 2,073,000 pixels and 4K is 4096 x 2160 = 8,847,360.

Then you would think that 4K is 4 times the resolution of 1080p (8,847,360 / 2,073,000 = 4)

But why is that when I drop 4K 1DC footage into a Premiere Pro CS6 1080p timeline, the scale of my 4K footage comes in at 50%? Shouldn't it be 25% scale in a 1080p sequence? It sounds to me like the 1080p sequence is looking at the height alone of the 4K footage, 2160, which is of course only twice as high as 1080.

Just to test, I tried scaling up my 4K footage within the 1080p timeline to 200% and of course the footage is quite soft looking.
But again, shouldn't that 4K footage be coming into the 1080p timeline at 25% (rather than 50%) if it were 4x the size of 1080p?

Can someone clarify this for me? Thank you very much in advance.

 

[J Davis]

the editor does not measure percentage scale as an area value ( 25% ) it measures it as a percentage of it width ( 50% )

 

[Nicholas Natteau]

Hi J Davis, thanks. When you say "editor" are you referring to one Premiere Pro CS6's windows? If so, are you referring to the timeline window?

 

[AndreeOnline]

Nicholas, regarding two times or 4 times... it's kind of both...

There are 4 times as many pixles in 4k footage compared to 2k footage. 1080p is slightly less, since it's only 1920 wide compared to 2048 for 2k.

The confusion comes from the fact that "4 times the size" comes from counting the area—the number of pixels. And to get to that you take the long side of the image times the short side, just like you did in your calculations.

But when you look that the individual sides of your footage you will see that 2k or 1080p is 50% as big as big as 4k side-for-side. Or, each side of 4k footage is twice as long as that for 1080p. And when you multiply 2 times longer with two times longer (for area), 2x2, you arrive at 4.

Premiere is reporting that one side of the footage is 50% as long, just like J Davis said, so everything is as it should.

 

[Nicholas Natteau]

Thanks very much Andree. I see what you mean.

So when scaling in Premiere Pro CS6, it's just the width that counts then? 4096 (the width of a 4K clip) being 200% that of 2048 (width of a 2K clip) or 213% that of 1920 (width of a 1080p clip).

Just so I have this right then:

Even though area wise 4K is 4 times the size of 1080p, when you drop a 4K clip into a 2K sequence, you have to resize it to 50% to fit it completely into the 2K frame:



And to fit a 4K clip completely into a 1080p frame, you would have to reduce it to 47% scale if you didn't want the edges (left and right) cut off:

 

[AndreeOnline]

Yes.

But I guess normally you'd just drag the footage borders and it will snap into place?

Since 4k is a different aspect ratio from 1080p you have to decide how to crop: either fit or fill. If you choose fit, you'll end up with black borders top and bottom if you shrink 4k to a 1080p frame.