When to resample?

[Jeff Deveraux]

Bare with me guys/gals, I'm still learning.

I love that RED has given us all these options for output in REDRUSHES, but I wonder how many we actually need.

So, I was just messing around with REDRUSHES and I confirmed some assumptions I have made. I assumed that exporting a Prorez 422 quarter debayer would look better than prorez 422 1280 x 720 scaled due to resampling. I rendered out one of each and, in fact, that was the case.

It seems to me that resampling causes the image to get slightly softer because it is not simply removing pixels. From what little I understand, resampling has to either add or subtract fractions of pixels. Now, with that logic, I should stick to 1k and 2k prorez files for editing and let compressor do the work for DVD or HD tape. This way, I am only resampling once and not resampling a resampled image.

If you feel I need some enlightening, please do so... I'm here to learn.


As a side note...
I also noticed that a prorez 422 quarter debayer (1K) is not quite 1/3rd the file size of a prorez 422 half debayer (2K). Shouldn't it be 1/4 the size?

 

[Deanan]

Resampling always has an affect on the image especially if the scales are not a nice multiple. by the nature of it, a resample uses many weighted pixels from the source to determine the output pixel.

Compressor will do the similar resampling to what RR is doing. The only difference being that in RR it happens before you output a file and in compressor, it's just done in another software.

Also, a quarter res vs a 720p resample means that you're scaling up the 720p so it should be a bit softer due to the scale up.

 

[Jeff Deveraux]

Resampling always has an affect on the image especially if the scales are not a nice multiple. by the nature of it, a resample uses many weighted pixels from the source to determine the output pixel.

Compressor will do the similar resampling to what RR is doing. The only difference being that in RR it happens before you output a file and in compressor, it's just done in another software.

Also, a quarter res vs a 720p resample means that you're scaling up the 720p so it should be a bit softer due to the scale up.

Deanan-
THX for the reply. I should have been more clear. My 720 render was from a half debayer. Doesn't that mean I was down scaling from 2k across to 1280 across.

 

[Jeff Deveraux]

Also, I learned from my HVX days that if imported 720 into a SD timeline it looked like crap. Whereas, if I edit in a 720 timeline compressor seemed to work much better for SD DVD.

 

[Deanan]

Thanks. They're both taking very different paths. The half debayer is a higher quality debayer that takes care not to be aliasy. The quarter is much faster but tends to be more aliasy and has the appearance of being sharper.