The blackest blacks (3 replies and 1 comment)
Technical question here: what is the secret to making blacks look really black on digital? What can you do on set and what can you do in the grade? Are there camera settings or filters that help or is it in the lighting and exposure?
Please have a look at David Mullens post only a few weeks ago, you will find it very interesting.
There is a technical answer and a perceptual one...
In digital, in a display gamma like Rec.709, black is 0 IRE, there is nothing blacker than zero. Anything pushed below 0 IRE just disappears, what is called "crushed". If you made a black title card with white letters, the black field would be 0 IRE on a waveform.
In a film print, the equivalent is D-Max (maximum density). You can't get a blacker black unless you do something like a silver retention process which adds additional black silver to the color dyes in the print.
So if the area in the image you want to go pure black is 0 IRE, it can't get any blacker. Any black with shadow detail isn't black, by definition it is above 0 IRE. So that's a different question, how to get dark shadow detail versus pure black. But generally detail that is just about to go black is in that 1 to 10 IRE range on a waveform.
Perceptual black is a different issue. An area looks blacker to the eye when it is next to an area with a bright highlight. In the days of slow film stock, when shooting night exterior scenes that ended up underexposed and push-processed, there were no true blacks in the print due to the combination of low printer light numbers and base fog levels. So cinematographers often included small points of bright highlights in the frame rather than just have large fields of murky, grey-ish black at night. The highlight made the surrounding darkness look darker to the eye and made it harder to tell the true black level. William Fraker often told stories about this, like putting distant tweenies in the far background of a dark airfield scene in "Bullitt" (1968) so there would be some hot highlights in the darkness, or in "War Games" (1983) when he needed the rear projection computer screens to go black instead of gray when the power was shut off, he had the art department put a neon border around the screen to create a bright edge that made the center look darker in comparison.
Creating darkness in a movie is both a creative and a technical act because perception is as important as technology.
But usually when this question gets asked, someone isn't really asking how to make pure black go black (just set it to 0 IRE), they are asking how to have dim shadow detail that rolls off into areas of black with minimal noise. That requires both lighting to create the mood desired and working at an ISO level that has acceptable (to you) noise levels in the shadows. And working around a standard contrast level for the display image, not something lower-contrast that is going to cause the shadows areas to be lifted up in luminance.
I'm talking about the final displayed image here. When recording log gamma for extended dynamic range, or raw converted to log for color-correction, keep in mind that log is not meant to be viewed as a final image, it is a storage format for exposure information. So if you shot a standard 11-step grey scale and looked at the log version on a waveform, black might be 10 to 15 IRE and white might only be 70 IRE, allowing the log recording to hold shadow and highlight information beyond the 10-stops of a broadcast display monitor (ignoring HDR monitors.). And you'd also see a lot more noise at the bottom end of the exposure in the log version because everything looks lifted when viewed on a Rec.709 monitor. Once a standard log to Rec.709 (or P3) conversion LUT is applied, the shadows get much darker and the noise is harder to see.
Often people have noise problems because they are working at a higher ISO and they are not judging the image on a calibrated monitor in the correct viewing LUT in a controlled environment, so they might underexpose more than they intend, and once they see everything on a bigger screen in the correct viewing environment and set the levels to what they now seem feels correct, the shadows look noisier than they did on the set. Or they opt for a lower-contrast color grade which ends up lifting the low end of the image, bringing out the noise. This is why pre-production TESTING is so critical, and viewing the results in something like the final display size. If you do that, you would end up picking an ISO and display gamma LUT that gives you the noise levels you want so you are free to light creatively for whatever look you want, assuming you have an accurate way to judge the exposures on set.
Thank you for taking the time to give me this detailed explanation, David. There’s a lot of food for thought here. Much obliged.