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What is the correct IRE value of 18% grey for Rec709?

jxh5760
Contributor

Clog2 correct exposure puts middle grey at 407/39.8%. 
the canon default clog2 to rec709 lut still puts middle grey at 407/39.8%, which makes the image look dark. 
if I move middle grey to 512/50%, the image looks too bright and washed out. 

so what is the technical correct IRE value of middle grey for Rec709 in a final image? 

thanks!

2 REPLIES 2

Nick2020
Product Expert
Product Expert

Hi jxh5760,
Thanks for checking in with us.

Our engineers recommend that 18% grey should land at 42 IRE on the waveform monitor for Canon Log 2.
That said, you are welcome to do your own tests, since there might be some variation in your monitor or shooting conditions. Since that's the case, some professionals will opt to apply a Rec709 LUT to the monitor and use that to set the exposure rather than dialing in an exact value for 18% grey.

Instead of focusing on 18% grey, you could try to keep your whites at or around 80-90 IRE, your skin tones at or around 40-50 IRE, and your shadows at or around 20 IRE. Feel free to adjust to taste after doing some tests to see how that works with your scene and your post-production workflow.

Thank you! I am trying to figure out how to achieve a technically correct exposure, regardless of the scene. 

Is there a specific way to achieve exactly 42 IRE with the C70? C70 false color sets 18% grey at 39.8 IRE. Zebras are not as accurate. 42 IRE is about 0.25 stop over 39.8. Setting AE shift to +0.25 sometimes can achieve this but not always since standard exposure calculated by the camera is not always accurate, so +0.25 will also be off. 

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