Web Analytics
Re: HDR question

Re: HDR question


alister@...
 


What people often do on the FS7 is to expose one or two stops over, and "print down" for monitoring and post (see this video from Convergent Design).

While this is a useful approach to reduce shadow noise, you are doing so at the expense of highlight latitude. If this approach has been taken, it is more likely that windows and practicals may be blown out, unless care was taken not to. And as Kevin says, if something is blown out in the rushes, it can be hard to make it look good in HDR.

But HDR isn’t just about highlights, it’s also about screens that can show the shadow range better, perhaps with better shadow contrast and this means noise can be more problematic in HDR than SDR as it is reproduced better. So the trick is to getting the right balance so that the crucial and all important mid range is exposed well.  It is a mistake to just look at the highlights and shoot avoiding clipping if this results in a compromised shadow or mid range, likewise it wouldn’t be good to shoot super bright for great shadows if that kills the highlights. You need to find the right balance and not be constantly obsessing over highlight clipping or excess noise, you need to find the sweet spot for the camera you are using, and this normally means getting the mid range right, just as you would in SDR. 

Most current HDR consumer displays struggle to achieve 1000 NIT’s and even if they do, this will only be over very small parts of the screen, so often limited to specular highlights or other “shiny bits”. If these are clipped no one is going to notice as that’s how they tend to look in the real world. Most real world HDR productions target 1000 to 1500 NITS for the final output, which is around 9 to 10 stops. So with most log cameras capable of capturing at least 12 useable stops maybe a touch more, there is still some exposure wriggle room. So if you feel that shooting at the equivalent of 1000 or 800ISO on an FS7 (+1 stop over base) helps with noise then I would continue to shoot that way as noise in the mid range, which makes up the majority of most images, will be a much more noticeable artefact than a few small clipped specular highlights that no current HDR screen can show correctly anyway. If you have a large, bright window in the shot then no HDR TV or monitor is going to deal with this well as it will hit the power limits of the display so it can’t be reproduced super bright and the brightness will be throttled back according to the displays power limitations and the MaxFall and MaxCLL metadata in the final material. So the key to good HDR is no different to good SDR, control the contrast in the scene, avoid extreme highlights and expose well so that you don’t deliver an excessively noisy file to post. 


Alister Chapman

DoP - Stereographer
UK Mobile +44 7711 152226
US Mobile +1(216)298-1977


www.xdcam-user.com    1.5 million hits, 100,000 visits from over 45,000 unique visitors every month!  Film and Video production techniques, reviews and news.


Join cml-raw-log-hdr@cml.news to automatically receive all group messages.