Hey @Dean …
Scott posted some Python code over here that provides an interactive example of the tone scale algorithm we’ve been playing with. Basically you have a few controls. Max and min luminance are the maximum and minimum luminance values of the display you’re using. The 18% gray luminance is the luminance at which you’d like to reproduce an ACES value of 0.18. With the current P3 48 nit max ODTs ACES=0.18 gets reproduced at 4.8 nits on the display. This was a choice … it could be moved up or down from there by shifting the entire tone scale left or right on the log / log plot. 10% of max luminance seemed about right for SDR, but with HDR the proper level is less clear. One can use the extended display dynamic range to increase the overall luminance of the image, display more highlight dynamic range from the scene, or a little of both. Give @sdyer demo a try and let us know what you think.