Day 4: 25 Insights in 25 Days Holiday Marathon
Blending Exposures For Better Results
In mid to late November of this year when Team Mixing Light sat down to discuss our annual holiday marathon, I was shocked that we had never covered a technique/option that I use all the time with RED footage – HDRx.
For DPs and colorists alike, one of the most frustrating situations is when you have a shot or scene that is stuck between exposures. Think of a scene inside a car or an interview with strong light filtering in through the windows in the background.
If the DP sets exposure for the windows the subject and things in the foreground are inevitably too dark, expose for the subject? Then the windows get blown out.
While experienced DPs and gaffers have all sorts of tricks up their sleeves including applying ND gels to windows, etc., sometimes you have to make a choice in exposure.
Among their many innovations, HDRx recording from RED is a good solution for handling these solutions on capable cameras, and that’s what I want to discuss in this Insight.
What is HDRx?
Put simply, HDRx is two different exposures carried in the same .r3d file.
The ‘A’ frame is a normal exposure – usually attempting to get most of the scene properly exposed. The ‘X’ frame is an alternate exposure usually 2-6 steps darker than the ‘A’ frame.
The exposure of the X frame is a shutter speed adjustment dictated by how many stops different the DP chooses the X frame to be. In a practical sense, the X frame is all about highlight protection.
For example, if in the A frame most of the shot looks great but windows are blown out, the X exposure being 2-6 stops darker can capture the windows at the correct exposure, but of course everything else will be much darker.
The net result in post (more on that in a moment) is that you have a shot with a higher dynamic range than would have been possible with a single exposure.
If you’ve ever shot in a bracketed mode on a stills camera – HDRx is a similar approach (albeit 2 exposures rather than 3-6 per a typical stills bracket). However, unlike a traditional bracket in a stills camera, the A & X exposures are stored in a single .r3d file.
While it might be tempting to push HDRx in the field to the extreme (6 stops), it gets harder in post to blend those exposures effectively without a lot of masking and other sacrifices having to be made.
Here is an article from RED explaining HDRx in more detail.
HDRx In Post
So what do you do with two different exposures in a single R3D file?
While there are couple different approaches, the basic idea is that you’re blending the A & X tracks or streams together – either overall or selectively via keying/windowing.
In the overall approach, you can achieve a blend through the camera raw controls for a RED clip and by using the Blend Type pulldown. The Blend Type pulldown lets you either use a simple average of the two clips or the RED proprietary blend called Magic Motion that has the additional benefit of blending motion (a great way of controlling motion blur). Once you’ve chosen a blend method, you can control the blend with the Blend Bias control.
For more control of an overall blend, you can also incorporate the X track/stream into a node tree by using a Layer Mixer node and some repatching of nodes/inputs.
If you want to be more selective with a blend between exposures no problem, using windows or qualifiers you can easily blend to clips more selectively.
Even though a DP might shoot a scene with HDRx enabled, you’re of course under no requirement to use it. Often I’ll grade the A track and if everything looks good I’ll ignore the X track altogether. In addition, I often try traditional highlight recovery tricks before moving on to the X track blend. DPs shooting RED often enable HDRx as an insurance policy!
Don’t get me wrong, it’s not that I don’t like HDRx, but depending on the subject material and with DPs who took it to the extreme – with 6 stops it can be hard(ish) to get good blends and on shots where you’re doing a lot of secondary work with HSL keys and windows, it can be a little tricky to make sure corrections are invisible and to stay organized.
While I’m going to show you HDRx workflow in Resolve in this Insight, HDRx workflow is possible in other apps like RED Cine X and even editorial tools like Premiere Pro thanks to the full-featured RED SDK.
Is This The HDR Everyone Is Talking About?
RED’s HDRx is a high dynamic range approach that as I mentioned is similar to photographic HDR by blending exposures together.
HDR video that everyone seems to be discussing these days has a similar goal of high dynamic range footage, but HDR video is different – putting more emphasis on single exposures and the latitude already being captured by high dynamic range cameras and how that information is displayed on a monitor.
I’m fascinated by HDR work and just this week and I’m starting a test project. During the 2015 Holiday Marathon we’ll be talking a lot more about HDR in a MailBag episode, as well as a few different Insights covering HDR essentials.
Comments or questions? Please use the comments below.