De-Bayer question...for Graeme

[John Allardice]

Dunno if this is a "wait till NAB" thing or not. Its more a question of how Redcine works internally.
When outputting to a resolution other than the one at which one originally shot the footage, is the scaling part of the de-bayer process?...What I mean is, is there any practical difference between de-bayering to 4k, then scaling in a 3rd party program...After FX, nuke etc... OR is the debayer and scale intrinsically linked within Redcine so as to give the perfect quality of output at your chosen target resolution?

Hope that made sense

J

[Graeme Nattress]

Makes sense - de-mosaicing is seperate from scaling. As for benefits - no idea.

Graeme

[GlennChan]

I would think that the downscaling quality depends on the algorithm you use. I might expect Redcine to do something like...

Footage comes in as 12-bit linear (linear as in linear light, not video gamma). De-bayer (footage still linear light). Rescaling could be done in the linear light domain, as it tends to look better when done that way (as opposed to rescaling after you apply gamma correction / gamma curves). The re-scaling step would ideally be GPU accelerated too.

Whereas if you do the rescaling in another program, there's addition overhead so it'll be slower. As far as rescaling algorithms go, there are different ones out there that are tradeoffs between aliasing, sharpness, and ringing. There are also tradeoffs in visual quality and in performance (a real sinc filter is slow; Shake doesn't do real sinc filtering, it cheats).

See
http://www.cambridgeincolour.com/tutorials/image-resize-for-web.htm

2- Mathematically, you might incur some loss due to rounding depending on how you get the 4k image into a 3rd party app. But in practice, this would be insignificant (the rescaling algorithm would make way more of a difference).

[Bruce Allen]

See also
http://www.fxguide.com/article315.html

For a similar article from a VFX end-user point of view.

Bruce Allen
www.boacinema.com