Grading and LUTs, etc.

[jcs]

The quality difference isn't a "myth" with respect to chroma re-sampling.  You're shooting to a sub-sampled format and when you import that into something like After Effects there are multiple ways in which this can be handled (and quality influenced).  This goes back to the DV codec wars where DV quality was not simply DV quality and not all codecs or applications were equal in their handling.  Whether or not to use YC cables versus composite for older video equipment is also semi-relevant (*).

 

 

The MTS image appears to show that chroma is not being interpolated from 420 to 444. While it's possible to throw a low-pass/Gaussian filter on chroma in post, ideally the chroma would use a high quality interpolater to make the final result as sharp as possible without ringing (e.g. bicubic sharper, Lanczos 2, etc.)). I did tests a while ago with 5D Mark III MOV's and it worked as expected- chroma looked properly upsampled to 444 (as others may have done comparing PPro to 5DtoRGB with Canon MOV's). Perhaps that MTS (or something about that particular MTS) told Premiere not to do interpolation (or the MTS importer path doesn't do it). A test might be to use ffmpeg or other tool to rewrap the MTS file as MOV and see if Premiere does proper chroma interpolation.

[see ya]

Premiere CS only upsamples chroma internally to 4:4:4 YCC if a filter is added. Cuts only or import export to a 4:2:0 codec will not involve 4:4:4 and export to RGB image then upsampling to 4:4:4 YCC first is unnecessary.

[jcs]

If that's the case then no advantage transcoding first. If doing cuts only then disadvantage to transcode first. Unless there's a performance issue, transcoding isn't needed with Premiere.

[Sean Cunningham]

Unless Premiere does it better than After Effects, which I doubt, it won't do as good a job, because After Effects does not, which has a better pipeline thru-and-thru than Premiere.  If you're just going to rely on the app to do the filtering.  And you don't have the tools really, in Premiere, to process luma and chroma independently of one another.

 

Odds are, if you're really concerned about quality though, you're not finishing in Premiere anyway so, carry on.

 

 

A test might be to use ffmpeg or other tool to rewrap the MTS file as MOV and see if Premiere does proper chroma interpolation.

 

 

The problem with this is MTS rewrapped as .mov have lower playback performance in some applications, on some systems, compared to the original MTS even though internally it's the same contents.  That being the case I'd take a little extra up-front processing and just go "all in" and convert to Prores rather than some half measure.

[jcs]

Looks like Premiere does decent scaling (Lanczos 2 + bicubic): http://blogs.adobe.com/premierepro/2010/10/scaling-in-premiere-pro-cs5.html . Not clear if they're doing the same thing in CS6 or CC. Would expect them to use their top quality when scaling up chroma.

 

It appears you can test it by adding a GPU RGB filter of some type (e.g. RGB Curves)- per yellow this triggers the chroma interpolation.

[Sean Cunningham]

That article appears to only be referring to resampling from spatial transformation.  That doesn't mean they don't switch to filtering when you engage a color effect of course but the text of that document is talking about the results from scaling, repositioning and rotation.  The 32bit linearization that occurs, that they describe, is necessary to preserve the luminance of small features that might otherwise be filtered away in a normal, integer operation with even the best filtering methods.

[jcs]

Not sure we're talking about the same thing- the link I referenced discusses scaling; I'm referencing scaling UV/CbCr up 2x (to match Y). Thus the 960x540 chroma gets scaled up to 1920x1080 via a filtered interpolator (Lanczos 2 + bicubic). Not clear what Adobe means by using both Lanczos and bicubic unless they use one to scale up and the other down. In any case they are both high-quality interpolaters.

 

32-bit integer has more precising than 32-bit float; float runs faster and is easier to code. My understanding is that everything in PPro is 32-bit float for the Mercury Engine. When using 32-bit float it won't really matter if it's linear or log, etc. Single-precision float's 23 bits of fraction is plenty (until someone makes a camera with 24-bit integer per color element ;) ).

 

Per yellow, Adobe doesn't bother converting 420 to 444 unless an RGB filter has been added to the sequence. Makes sense I suppose for performance and minimum changes to the image.

[Sean Cunningham]

The link you posted above is discussing the filtering done on spatial scaling and otherwise transforming the image, not chroma scaling.  I don't think you can assume the same filtering applies.  Perhaps you posted the wrong link but nothing in that document implies these methods are used to scale up under-sampled chroma.

[jcs]

Scaling chroma is the same math as scaling RGB (each channel is scaled independently). Agreed we can't make assumptions, however that's how I'd write the code (using Lanczos or bicubic:Catmull-Rom or similar).

 

A fast Catmull-Rom bicubic shader:

http://vec3.ca/bicubic-filtering-in-fewer-taps/

http://pastebin.com/raw.php?i=YLLSBRFq

 

The excellent GPUImage (which runs on iOS- same shaders can run on desktop GPUs) has a fast Lanczos shader: https://github.com/BradLarson/GPUImage

 

Adobe's code is likely a bit different, though they're implementing the same types of sinc and bicubic shaders for scaling when apparently any PPro RGB effect is used. The other options are nearest neighbor (your example) and bilinear (fast, but  doesn't look like they are using it).

[Sean Cunningham]

Tweaking the Sequence preference to show full quality doesn't appreciably increase chroma smoothness on an MTS clip in PPro CS6.  Adding a 32bit RGB filter and giving it a nudge, to try and force some kind of resampling and smoothing, does not seem to show an increase in smoothness.  5DtoRGB transcode still wins.

[jcs]

Thanks for testing- I'll examine my FS700 MTS footage more closely next time I edit.

Perhaps someday Adobe will support custom pixel shaders for Premiere- would allow a fast real time solution (ideally supporting multipass shaders in one Effect). Their SDK for plugins didn't provide a means to hook into the Mercury Engine pipeline to provide real-time processing last time I checked (need access to OpenGL textures, etc.).

[jonpais]

Here's a short tutorial I created for those having trouble importing XML files into Resolve from FCPX

 

http://jonpais.wordpress.com/2014/03/22/how-to-import-xml-files-into-resolve-without-crashes/

[Bioskop.Inc]

So finally got around to playing with some BM Pocket ProRes (Film) footage.

The edit is quick'n'dirty & was just trying to come up with different grading possibilities.

All done within FCPX using the colour board and/or some of the presets - No LUTs.

See what you think - do you really need LUTs?

 

On an aside, I did try Film Convert & I was very impressed how it dealt with the footage, espcially the highlight/shadow roll off.

[Axel]

See what you think - do you really need LUTs?

 

 

I don't know, but your clip proves little. One time there is a green cast, one time a blue cast, one time sepia. I would have preferred a whole sequence in one style.

 

Two weeks ago, I had my first (unpaid) job with the Pocket, a series of interviews under different light conditions. It had to be edited within two days, and I was glad to be able to apply the Rec709 LUT on an adjustment layer prior to grading. What I found out is, that the LUT doesn't cut off highlights and crushes blacks or whatever, it just gives you all at once a 'normal looking' video as a starting point. Below that, it was still possible to recover seemingly clipped areas (I used 95% zebra for ProRes and more or less ETTR to avoid noise).

[Bioskop.Inc]

I don't know, but your clip proves little. One time there is a green cast, one time a blue cast, one time sepia. I would have preferred a whole sequence in one style.

 

Yeah i was just messing about really so wanted to try different looks. I tried some LUTs but most just left me a bit...well, not really impressed. The only thing that spoke to me was Film Convert, but my wallet ain't having it!

 

All this footage was done with available natural light, which isn't your friend with this camera - however, i do like the film-like noise.

Those preset WB settings are shit!