Redcine Internals

[Stacey Spears]

I am a firm believer in linear light. All of my custom video tools work in at least 32-bit float and linear light. According to Stu's blog, who is also a proponent of linear light, color correction should actually be done in gamma corrected space. http://prolost.blogspot.com/2005/01/color-correction-in-linear-vs-gamma.html

My question is, does Redcine perform primar color correction in linear or gamma corrected space?

When outputting OpenEXR, is it 16-bit or 32-bit? Is there a choice? Is lossless compression an option?

 

[GlennChan]

I think Redcine will perform color manipulations in the right color space. The right color space depends on the phenomenon... sometimes it is linear light, sometimes it is sort form of gamma correction or perceptual curve.

And sometimes you need to do calculations both in linear light and with some form of gamma correction (or perceptual curve)... e.g. I've found that saturation is one of those things. Or if you look at the CIE L*a*b* color space, there are calculations both in linear light and with a perceptual curve (power function of 3.0).

Anyways...
A- I would expect Redcine to have image processing performed in the ideal color space. At least what the developers think is the ideal color space... sometimes the color science is not clear so there can be different interpretations as to what the ideal color space is (e.g. CIE Lab, Luv, CIE CAM, Munsell, etc. etc.).

B- (Presumably) After processing, the output is converted from its internal color space (whatever it is) to what you specify. What output color space you specify shouldn't change the internal image processing / shouldn't change the internal color space.
If not, then the underlying image will be different depending on what output format you choose... this would be annoying to say the least. (e.g. if you output to log and convert to linear, that image wouldn't be the same had you outputted linear in the first place. The sensible behaviour would be that linear output looks the same as log output converted to linear.)

2- Color matrix explanation:

http://www.dvxuser.com/V6/showthread.php?t=70528

Note that the Red will do this correctly, as opposed to the shortcut method most current video cameras do (AKA cheating).

3- As far as I know, the image processing Redcine will do is:
de-bayer
white balance, with white point adaptation
color matrix
Highlight recovery

re-scaling (probably linear light??? Graeme?)
sharpening
output curves on RGB (e.g. rec. 709, log, linear light transfer functions; with user-definable curves on top of that)

 

[GlennChan]

Stacey, please check your private messages.

2- For other people reading this thread, Stacey is one of the authors behind the article on the infamous chroma bug. IMO that's pretty cool.
http://www.hometheaterhifi.com/volume_8_2/dvd-benchmark-special-report-chroma-bug-4-2001.html

 

[Graeme Nattress]

Answer is:

Linear Light:
Demosaic
Colour matrix and exposure
curves, brightness and contrast occur in a custom (appropriate for their function) gamma space
final gamma space conversion to 709, REDLog, PDLog etc. or leave as linear light.

Highlight recovery is done in raw linear space (has to, as it has to work and go through the colour matrix to get the right overall colour temperature - tricky stuff).

Scaling in RedCine is done post-gamma. Scaling to 2k from raw 4k in RedAlert will be done in linear light as it's working on a RAW data extraction process.

Graeme

 

[Stacey Spears]

Thank you.