Color Shifts With Knee-Mode ON

[Joachim Claus]

I use Barry Green's scene file 6 (from his proposal for matching colors to GH4). which I have slightly modified as follows (Barry's values in brackets):
Master Detail -6 (0)
Detail Coring 2 (1)
Chroma Level -9 (-12)
Master Ped -4 (-9)
Gamma Mode Film-Like 3 (Cine-Like V)

In a number of outdoor recordings on sunny days with some more or less blue sky, I observed shifts of the blue sky from blue towards turquoise/cyan. With some research and tests I found, that this is caused by exposures to high brightness values when Knee Mode processing is activated to Manual or Auto. It can massively affect the recorded video which in some cases becomes unusable.

A first screenshot (A1260001) shows a scene in bright sun and clear sky, one without a grey filter set, the second (A1260002) with grey filter set to 1/4.

I a further Test on a partly sunny day I shot with grey filter 1/4 two clips, one with Knee-Mode Off (clip 01440014), and another one with Knee-Mode Manual (96/85) (clip 01440016). When Knee-mode processing is activated, the blue sky is again shifted to turquoise/cyan.

This experience has caused, that I will avoid Knee-Mode processing whenever possible.

Joachim