Canon C200 proper exposure in RAW with WFM, Proper IRE for 18% gray

[yvesbernas]

Hi

Concerns: Canon C200 proper exposure in RAW with WFM

Some  DOPs like Rubidium say: expose an 18% gray card at 42IRE  when preset at C-log3 because this is what  the canon papers recommend for C-Log2 and since RAW is recorded in C-Log2 in this camera, the IRE should be at 42 . (Cinematographer Ben Schubert also recommends 42 IRE but does not specify the preset !).

I have my doubts on all this because IRE values on the waveform monitor depend on the preset : C-Log3, C-Log, Rec709 or “OFF“.

Since there is no preset  C-Log2 on the C200, you cannot use the recommended value of 42 IRE, you should use the recommended  mid grey level value for the chosen preset.

On a graph published by CANON  showing  curves for “10 bit code value” versus “Relative stop from 18% grey” for BT709, C-Log, C-Log2 and C-Log3 (see pic below), you can read the  10bit code value for a zero deviation from 18%grey (middle bold vertical axis, which is the  10bit code value value for an 18% grey)  and convert it to IRE. This yield approximately 35 IRE for C-Log3, and 44 IRE for BT709 (and  42 for C-Log2).

So my guess is that if you preset to Rec709,  you set the exposure so that the 18%grey card shows 44 IRE on the waveform monitor.

Or if you preset C-Log3, the IRE should be 35 (and not 42 like Rubidium says. Ben Schubert  does not specify the preset for his recommended  42 IRE ).

Am I correct or did I miss something ?

[yvesbernas]

Hi

Concerns: Canon C200 proper exposure in RAW with WFM

Some  DOPs like Rubidium say: expose an 18% gray card at 42IRE  when preset at C-log3 because this is what  the canon papers recommend for C-Log2 and since RAW is recorded in C-Log2 in this camera, the IRE should be at 42 . (Cinematographer Ben Schubert also recommends 42 IRE but does not specify the preset !).

I have my doubts on all this because IRE values on the waveform monitor depend on the preset : C-Log3, C-Log, Rec709 or “OFF“.

Since there is no preset  C-Log2 on the C200, you cannot use the recommended value of 42 IRE, you should use the recommended  mid grey level value for the chosen preset.

On a graph published by CANON  showing  curves for “10 bit code value” versus “Relative stop from 18% grey” for BT709, C-Log, C-Log2 and C-Log3, you can read the  10bit code value for a zero deviation from 18%grey (middle bold vertical axis, which is the  10bit code value value for an 18% grey)  and convert it to IRE. This yield approximately 35 IRE for C-Log3, and 44 IRE for BT709 (and  42 for C-Log2).

So my guess is that if you preset to Rec709,  you set the exposure so that the18%grey card shows 44 IRE on the waveform monitor.

Or if you preset C-Log3, the IRE should be 35 (and not 42 like Rubidium says. Ben Schubert  does not specify the preset for his recommended  42 IRE ).

Am I correct or did I miss something ?

.

[Anonymous]

Perhaps you should post this question to the Video section.

[yvesbernas]

Yes, thanks.

[John_Q]

Hello yvesbernas,

Based on the chart and information provided by Canon, I would agree with your assessment.