The first thing I checked was to make sure that middle gray actually fell where it was supposed to: Still, some say that mid-tones look a little dark on the Sony F55 when exposed normally, and the reduced contrast that comes from placing an extra stop of information between 40IRE and 80IRE may be why. In this case Sony gives use six stops of dynamic range above middle gray where the Rec 709 spec only calls for about 2.5, and they roll off contrast nicely in the highlights while preserving a fair amount of contrast in the mid-tones. #LUTCALC ART ADAMS LC709A FULL#What’s interesting to see is how manufacturers find ways to cram a camera’s full dynamic range into the Rec 709 spec in usable ways. We’re way beyond strictly adhering to the Rec 709 spec it’s hideously outdated, and we’d be crippling ourselves artistically if camera manufacturers truly followed it. The difference here is that instead of two stops between 40-80% there are actually three! Zone VI should be at 60% but looks to be around 53-54% instead, and Zone VII should be at 80% but instead falls at 68% or so. The two stops below middle gray fall on 27% and 17%, which is where Rec 709 expects to see them. Notice how many stops fall between 40IRE and 80IRE. Here’s what the LC-709 Type A look profile looks like: That seems to be the key: if the middle five stops of dynamic range (middle gray plus/minus two stops) land roughly in a range between 20 IRE and 80 IRE, mid-tone contrast looks realistic on an average HD display. In the Rec 709 800% chart above you’ll see that Zones III, IV, V and VI land exactly on the IRE values I show in the chart above. (There’s some room for cheating, but as a general rule that’s the way things seem to work.) The closer the mid-tones in a gamma curve land to those values the more “natural” they’ll look on a Rec 709 display. What I notice from this chart is that the first two stops above middle gray cover about 20IRE each (if middle gray is 40IRE, then one stop brighter than that falls at 60IRE and two stops brighter is roughly 80IRE.) and the two stops below middle gray are roughly 10 IRE each (one stop down is 27 IRE, and two stops is 17 IRE-so, in theory, we could round those off to 30 IRE and 20 IRE). This chart is based on a formula I was given by Charles Poynton.Įvery time a reflectance value doubles or halves it changes exposure by one stop. One is the Xyla dynamic range chart, with which I can quickly visualize any gamma curve and plot the full dynamic range of any camera: I do a lot of consulting for DSC Labs and as a result I have a lot of their charts at my disposal. What can a manufacturer do when faced with the dilemma of building better cameras whose footage will primarily be seen on displays whose design specs are hopelessly outdated? They can cheat! And cheat they do: they take advantage of what our eyes do anyway, which is to increase contrast in the mid-tones, where we’re most sensitive, and reduce it in the highlights and shadows. The problem, though, is that unless you’re transferring HD to film or projecting in P3 you’re limited to six linear stops of dynamic range in your “bit bucket,” which is the most that can be seen on the average Rec 709 display. SIX STOPS! The worst cameras out right now capture ten stops. The original Rec 709 spec was defined to capture six linear stops of scene referred brightness information. True Rec 709 is the dumbest mode you can ever opt for in a camera. This is the same image but with different contrast and colorimetry applied. Rec 709 800%, 1D LUT applied in “Custom” mode. Here’s a JPEG created from a DPX file output from Sony Raw Viewer: Still, knowing how easy it is to fool the human brain-and given how, theoretically, I’m using one of those in the course of my work-I opted to take a closer look to see if there was something to these complaints. I regularly give flesh tones just a little bit more exposure anyway, so I figured that exposing them normally would look a little dark to my eye as that’s not the way I normally work. While flesh tones didn’t pop as much as I’d normally like they looked acceptable to me. One commenter said the “normal” exposure looked as much as one stop darker than they expected. I got the same feedback after showing the flesh tone tests seen in my last article. #LUTCALC ART ADAMS LC709A ISO#The base ISO of 1250 looked “too dark” for his tastes when he exposed strictly by light meter. #LUTCALC ART ADAMS LC709A SERIES#Not long after the Sony F55 became widely available the DP of a major TV series stated on the Cinematography Mailing List that he sets the camera at its default ISO of 1250 but sets his meter for ISO 800, as that gave him exposures that looked consistent with what he expected from a camera or from film stock. Several people commented that the base flesh tone exposures in my CineGear presentation looked “dark.” I did a little research and I think I know what’s going on…
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