These are all taken from an excellent series of articles by Art Adams (now cinema lens specialist at ARRI) on HDR and none of the guidelines will be new to anyone who’s been following our blog, but here goes.
- TEST, TEST, TEST. Lens and sensor combinations should be tested extensively in advance. Some lenses work better with some sensors than others, and this has a demonstrable impact on image quality. Not all good lenses and good sensors pair optimally, and occasionally cheaper lenses will yield better results with a given sensor.
- CUT THE CAMERA’S ISO IN HALF. Excess noise can significantly degrade the HDR experience. The best looking HDR retains some detail near black, and noise “movement” can cause loss of shadow detail in the darkest tones. Rating the camera slower, or using a viewing LUT that does the same, allows the colorist to push the noise floor down until it becomes black, while retaining detail and texture in tones just above black.
- SHOOT IN RGB 444 OR RAW. The Y’CbCr encoding model is popular because it conceals subsampling artifacts vastly better than does RGB encoding. Sadly, while Y’CbCr works well in Rec 709, it doesn’t work very well for HDR. Because the Y’CbCr values are created from RGB values that have been gamma corrected, the luma and chroma values are not perfectly separate: subsampling causes minor shifts in both. This isn’t noticeable in Rec 709’s smaller color gamut, but it matters quite a lot in a large color gamut.
- BIT DEPTH. The brighter the target monitor, the more bits we need to capture to be safe. It’s important to know how your program will be mastered. If it will be mastered for 1,000 nit delivery, 12 bits is ideal but 10 might suffice. Material shot for 4,000 nit HDR mastering should probably be captured at 12 bits or higher. (It’s safe to assume that footage mastered at 1,000 nits now will likely be remastered for brighter televisions later.) When in doubt, aim high. The colorist who eventually regrades your material on a 10,000 nit display will thank you. ALWAYS capture in raw or log, at the highest bit depth possible, using a color gamut that is no smaller than P3.
- WORK WITH CAMERA NATIVE FOOTAGE FROM SHOOT THROUGH POST. It’s a good idea to work with camera original data all the way through post. PQ transcoding should only happen as a final step when producing deliverables.