Crop or compress

[Irri]

It has been suggested that it is better to crop 2K to 1080 rather than compress.

What about 4K? Is it better to export as 2K then crop or is compressing from 4K to 1080 just as good?

 

[Rob Lohman]

When you say compress are you talking about a scale / resample?

In general a crop is better to go from 2K to 1080 since you would have to do a very small resample which might not look so nice. It's a small crop also so you don't loose too much.

For 4K to 1080 you could do a resample, or a crop + resample. Depends on the framing and how much you can loose. I don't think a 4K to 1080 downsample would be too bad.

 

[Kevin Halverson]

Still, non integer scaling is much more processing intensive compared to an integer approach and would seem more likely to exhibit artifacts. I would always vote for an integer scale and crop if given a choice (it gives you some framing options in post too).

 

[BASSAM MSSALATIE]

When you say compress are you talking about a scale / resample?

In general a crop is better to go from 2K to 1080 since you would have to do a very small resample which might not look so nice. It's a small crop also so you don't loose too much.

For 4K to 1080 you could do a resample, or a crop + resample. Depends on the framing and how much you can loose. I don't think a 4K to 1080 downsample would be too bad.

how you can do cropping ?:help:

 

[Irri]

Yes, I mean resample.

I am outputting to 1080, but want to shoot 4K for the DoF. I saw someone mention that it would be better to just crop from 2K to 1080 becuase it avoids a resample.


I guess my thinking was along the lines of khmuse's that it might be better to resample to 2K then crop in order to do integer scalling (if that's what is going on inside the program), rather than going straight from 4K to 1080.


The other thing is that if we crop we get a sort of safe area to do slight reframes in post. I was thinking I could set the safe area markers in the camera to represent this so it would be more like a film camera ground glass.

 

[Rob Lohman]

how you can do cropping ?:help:

In what program? REDCINE supports it, I assume Final Cut Pro does as well

 

[Rob Lohman]

I saw someone mention that it would be better to just crop from 2K to 1080 becuase it avoids a resample.

That would be better with a 2K source image for sure. For a 4K source it might not be the case, assuming a 4K 16:9 source you have three choices:

4096 x 2304 --resample--> 1920 x 1080
4096 x 2304 --crop--> 3840 x 2160 --resample--> 1920 x 1080
4096 x 2304 --resample--> 2048 x 1152 --crop--> 1920 x 1080

With the last two options you loose a bit of image since you crop something out. With the first one you don't....

I guess my thinking was along the lines of khmuse's that it might be better to resample to 2K then crop in order to do integer scalling (if that's what is going on inside the program), rather than going straight from 4K to 1080.

As with everything it depends on your requirements (can you afford to crop) and if the quality difference is big enough (probably doubtful with 4K -> 1080 if you're using high-quality resample algorithms). As always run tests YOURSELF and make up your OWN opinion on what you find best. What might work for me might not work for you...

There is no single best or worst answer... it all depends

 

[Irri]

Thanks for the reply Rob. I don't see any problem with cropping if that's what is being framed for. I did run a test today and couldn't really see a difference between 4K-2K-cropped 1080 and 4K-1080. My broadcast monitor isn't HD though.

It does bring another question to mind: would 2K cropped to 1080 be better than any of the options for going from 4K to 1080, and if so, wouldn't that be a reason for wanting 2K scaled?

 

[Zach Hilton]

That would be better with a 2K source image for sure. For a 4K source it might not be the case, assuming a 4K 16:9 source you have three choices:

4096 x 2304 --resample--> 1920 x 1080
4096 x 2304 --crop--> 3840 x 2160 --resample--> 1920 x 1080
4096 x 2304 --resample--> 2048 x 1152 --crop--> 1920 x 1080

As for speed in exporting, what have you and others found to work better? Is one of those options faster or are they all relatively the same?

 

[Mike McCarthy]

4096 x 2304 --resample--> 1920 x 1080
4096 x 2304 --crop--> 3840 x 2160 --resample--> 1920 x 1080
4096 x 2304 --resample--> 2048 x 1152 --crop--> 1920 x 1080

With the last two options you loose a bit of image since you crop something out. With the first one you don't....

Theoretically, the second and third options SHOULD produce identical results, and cropping first in option 2 should be the fastest, as less data is being resampled. I would find it hard to believe that cropping will produce a better image when going from 4K to 1080p, although I understand the arguement for 2K to 1080p. It becomes a Nyquist oversampling thing though, where once you sample at twice the required frequency, all possible data is there.