Oversampling

With all these new high resolution video sources out there, it great to know you can pan into a 2K, 3K or 4K frame and still deliver sharp results at your 720p/1080i output.  However, this oversampling advantage can be easily lost with incorrect use or setup within your NLE. We often see user setups that run the larger source media on a timeline that matches the target resolution, e.g. 4K source in a 1080i/p timeline.   This seems to be an obvious configuration, but I'm going to point out why this is the wrong way to setup your project, particularly if you want any oversampling advantage when re-cropping a larger frame.  Using Premiere Pro as an example, dragging 4K media into a 1080/2K timeline defaults to center cropping the image. This is an annoying default as you likely don't want any cropping for most clips, other than a few scenes that might need a little re-framing, so the 50% center crop default is a nuisance.  The are two solutions to address this center crop:
1) Go through all your clips on the timeline, adding a motion filter to re-frame back to the entire image (particular trickly to do fast with mix resolution sources.)  
2) Use the neat feature, "scale to frame size", which can be set up as the default for these types of projects.

If you pick 2), as it is certainly the easiest, you have lost all your oversampling advantages.  Really!  This scale happens BEFORE any of your timeline based filters see the data.  So 4K images on a 1080 timeline becomes only a 1080 source when you zoom in; push in more than 20% and the image will get soft.  There is nothing wrong with 4K on a 1080p timeline in this mode, as long as you remember to turn that feature off when doing any re-cropping, it is just too easy to forget.

If you go with solution 1), you still have your oversampling benefits for re-framing.  But now you have to be careful as the NLE is doing the resize not the importer, so you have to make sure all your scaling filters are deeper than 8-bit, otherwise you will have lost precision.  Adding a motion filter would seem best, as the Premiere motion filter does support 32-bit processing -- within Prospect HD/4K you can turn on the feature that displays the depth of the filter stack (handy to confirm you are maintaining quality.)  This additional scaling step can make things slower during your edit.

The better solution is to do your edit at your largest source resolution, i.e. editing 4K at 4K and 2K at 2K.  Set the "scale to default size" on so any lower resolution media (e.g. over-cranked sequences) are scaled to fit (no issues with the upscaling.) There are no limitations to doing this, particularly as Prospect 4K already dynamically decodes larger source data to half or quarter resolution as needed for editing speed.  There are many advantages, such as freeing the range of output options for frame size and frame aspect, to be performed at maximum quality.  4K within a default scale to frame 1080 project, will have a little poorer 720p exports, as scales would be 4K to 1080 then 720, rather than 4K oversampling and scaling directly to 720.   I've received some feedback to suggest some feel that zooming into 4K frame in a 4K timeline would result in softer images than the same source in a 2K timeline; they are missing the fact that oversampling happens upon export to whatever the target resolution may be, not how it previews at 100% pixel view on the timeline.  When pushing into a 4K frame, within a 4K project, you can check your sharpness at 1080/2K by setting the program window view to 50%, or look at the 1080p feed over HDSDI, both will allow you to see if you are pushing in too far and preview the quality of the final output.

While instinct tells us for most projects a 1080p export will be plenty of resolution, that doesn't automatically extend to being the ideal timeline format, particularly for oversampled re-framing.