Pepijn is right with the diagnosis of the problem.
However, the correct way to do this conversion, would be to apply 709-xyz lut and render tiff as RGB.
The conversion itself is fairly standardized, but it’s critical to have a properly calibrated 709 monitor. If you don’t have that, there is no telling what will come out.
What’s more, you’ve still got the issue of the exhibiters calibration to contend with. Though I think theater owners tend to be pretty good about that.
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