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 HDRx™ Overview...
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PostPosted: Wed Jan 05, 2011 6:22 pm    Post subject: HDRx™ Overview... Reply with quote

Posted online by RED's Jim Jannard:

HDRx™ Overview...

"So what exactly is HDRx™?

HDRx™ is a RED invention that is built into every EPIC and Scarlet camera giving the user an option for extended dynamic range when the situation calls for it… from 2 to 6 stops over native by preset.

How does HDRx™ work?

In a single camera, HDRx™ simultaneously shoots two image tracks of whatever resolution and frame rate you have chosen. The primary track (A-track) is your normal exposure. The secondary track (X-track) is a "highlight protection" exposure that you determine in the menu settings. You select the amount of highlight protection you need in stops… 2,3,4,5, or 6. Each stop represents a stop less exposure in shutter speed. Example… if you select 2 and your primary exposure is 1/48th sec, the X-track will be two stops less exposure at 1/192 sec. The ISO and aperture remain the same for both exposures.

During recording, the two tracks are "motion-conjoined", meaning there is no gap in time between the two separate exposures. If they were two alternating standard exposures, there would be a time gap between the two tracks that would show up as an undesirable motion artifact. Both tracks (A & X) are stored in a single R3D. Since there are two exposures, the camera is recording double the amount of frames. For example, if you are shooting 24fps, the camera is recording 2-24fps tracks, the data equivalent of 48fps.* After combining the two tracks for playback you see only one 24fps motion stream.

Once I record HDRx™... what do I do with it?

The power of HDRx™ is the multiple options you have to use it.

1. Combine the two tracks in post tools like REDCINE-X, Storm or any other application that supports the SDK to create "Magic Motion" (see below). This blending of the two tracks comes with a slider so you can decide in post just how much of each track you want to use. A preview window shows you the result of your selection. You can also view each track individually.

2. You can combine the two tracks using MNMB (More Normal Motion Blur). MNMB is designed to emulate the motion of a traditional camera with full motion blur. This is a tool created by The Foundry (creators of Nuke) that uses a new motion estimation algorithm designed specifically for HDRx™. The shorter exposure (sharper image) is blended to match the motion blur of the normal exposure. Again, the preview window shows the combined result or each track individually.

3. You can use the X-track separately (sharper image) for motion tracking, then combine with the A-track as in #1 or #2 above… or ignore the X-track altogether.

4. You can combine with a variety of additional new tools created by Graeme Nattress for a multitude of creative options.

Exporting to EXR will give you a multi-view EXR with both exposures (like a stereo EXR).

So what is "Magic Motion"?

Shooting 24fps and 180 degree shutter on film or digital is an illusion. It is not really the way we see motion. Ask someone to stand in front of you and swing their arm over their head from one side to the other. If this was shot traditionally at 24fps at 1/48th shutter all you would see is a constant motion blur until the arm stopped. But that isn't what your eyes actually see. You see both motion blur AND sharper references to the arm and hand all along the path. "Magic Motion" is much closer to what the eyes see… the combination of motion blur (A-track) and a sharper reference (X-track)… with the bonus of extraordinary dynamic range not seen in any motion capture camera.

Note: If you ignore the X-track completely, you will have a standard exposure with 13 stops of native dynamic range from the EPIC… just as if you had not turned HDRx™ on. For this reason, we encourage the A-track exposure to be "normal". It gives you the most options, including "turning off" HDRx™ (the X-track). If you are tempted to shoot "over-under", you are then fully committed to HDRx™. While no one will call the police on you if you do this, your options are dramatically reduced.

So what are the downsides to HDRx™?

1. Since you are recording twice as many frames, your maximum frame rate, minimum REDCODE ratio, and maximum record time on your media will be cut in half.

2. Limitations. MNMB is more effective than Magic Motion with very fast moving, bright objects in a dark environment. Can you break HDRx™? Sure. Just like you can pan too quickly with any 24fps camera. All digital cameras have to deal with judder. We got used to film grain to the point where we thought we actually didn't want to give it up. Learn the limitations just like everything else. Then shoot 18 stops of dynamic range and show all your friends what your camera can do.

Casey Green
RedCam Central Founder
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