Note: There is something up with the frame grabs. For some reason they are very dark. I’ll look into this in the morning and get some more accurate grabs online.
First of all let me say thanks to Ben Allan on CML list for getting me thinking about this. He has already started experimenting with creating a log style Picture Profile for the EX1. All the setting you’ll find here are my own work and based on tests done with real scenes and some dodgy home made latitude test charts 😉
Ben’s musings on CML made me consider what S-Log is. In essence it is nothing more than a clever gamma curve that allows you to capture a greater dynamic range than is normally possible with conventional gamma curves. The reason why the standard gamma dynamic range is normally constrained is in part simply because if you record too large a dynamic range and then show it on a conventional monitor or TV, it simply does not look right. So to make it look right it must be graded in post production. In order to do a significant grade in post, the quality of the recording has to be good enough to withstand a fair bit of pulling and pushing. As a result 10 bit recording is recommended (however it is still possible to work with lot with top quality low noise 8 bit recordings, not that I would recommend this). Anyway as both the standard PMW-F3 and EX1/EX3 have 10 bit outputs I decided to see if it was possible to come up with a picture profile that would mimic a Log curve and then see if it actually brings any real world advantage.
First up I experimented with the F3. I already have the S-Log option, so this gave me a benchmark to work against. To mimic S-Log you need to increase the gamma gain at the lower end of the curve, you can do this with the Black Gamma function. I know that with S-Log the cameras native ISO is 800 as this is the sensitivity at which maximum dynamic range can be realised with the F3’s sensor. So I started my experiments at 800iso. I could bring up the shadow detail with the Black Gamma but I notice that I appeared to be trading off some highlight handling for shadow information, so while the images kind of looked like S-Log, they did not really gain any latitude.
During this process I realised that my mid range sensitivity was now a lot higher than with genuine S-Log, so I decreased the camera gain so I was now at 400iso and started tweaking again. Now with Black Gamma all the way up at +99 I was seeing around 1 stop further into the shadows, with no impact on highlight handling.
When I tested my new Picture Profile on a real scene, exposing as you would S-Log with mid grey at 38% I was very pleased to find some very similar images that do grade quite well. As well as the Gamma tweaks I also incorporated a few other changes into the profile to increase the overall grade-ability.
There is a definite improvement in shadow reproduction. It’s not as good as real S-Log, but it does give a very useful improvement for those without S-Log. One interesting point is that the exposure between the two log frame grabs posted here is not changed, so even though the camera is set at 400iso, when the picture profile is applied the camera behaves more like an 800iso camera and exposure should be set accordingly. I think my PP (which you can download at the bottom of the page) brings a little under a one stop improvement in DR, real S-Log is about 2 stops.
If you click on the image captures you can view them full frame. When you compare the AC-Log and Cinegamma 4 images you should be able to see more shadow detail in the tree on the right of frame with the AC-Log yet the sky is further from clipping as well.
So what about the EX1 and EX3, can the same be done for them? Well this is much more of a challenge as the EX cameras are much noisier. Simply bringing up the Black Gamma does help you see into the shadows a bit better but it comes at the cost of a lot of extra noise and really makes it un gradable. Normally I don’t recommend using negative gain as it can reduce the dynamic range of the camera. But I figured if I use negative gain and then increase the gamma gain that should cancel out any dynamic range loss. To then avoid the usual -3db reduction in highlight performance I adjusted the overall gamma gain to return the peak output level to 109IRE. After a bit of fiddling around with my test charts and waveform monitors I could see that it was possible to gain a small amount of dynamic range, a little under 1 stop, however there is an overall increase in the noise level of about +4db. Now that doesn’t sound too terrible, but to gain the extra stop of DR you have to under expose compared to standard gamma’s, typically with S-Log you would put mid grey at 38% (use the centre spot meter on the EX1/EX3 and a grey card). This works reasonable well with this fake log picture profile. The problem however is that when grading you may find that you have to add still further gain to bring skin tones to a normal level and this will accentuate the noise. You could use something like the Neat Video plugging to reduce the noise and in this case I think this sudo Log picture profile could be handy in tricky lighting situations. The EX1R Log picture profile, to work correctly MUST be used in conjunction with -3db gain, any other gain setting and you will loose dynamic range. Again like real S-Log, 10 bit external recording is desirable, but why not play with the picture profile and try it for yourself. It is a bit experimental, I’m not convinced that the extra stop of DR is worth the noise penalty on the EX1R, but then I’m spoilt as I have an S-Log F3.
I have uploaded both the F3 and EX1R picture profiles into a single zip file that you can download below. You will need to have an account on xdcam-user.com to download them, or register for a new account first. Un-zip the package and copy the SONY folder to the root of an SxS card, so you should have both a BPAV folder and a SONY folder in the root directory. The cameras will need the latest firmware versions to load the single profile directly. In the Picture Profile menu choose an empty PP and then in the bottom PP menu chose “load”.
[downloads_box title=”F3 and EX1R Log Picture Profiles”]
F3 and EX1R Log like profiles