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Tuesday, June 15, 2010
Winning the Gamma Game
The Sony Tech Guy | 06/15
Sony HyperGamma throws luminance a curve
This scene ranges from 4 stops over key to 5 under. HyperGamma holds it together.
How do you capture high-contrast exterior day shots without blowing out the highlights or crushing the blacks? What’s the secret to recording low-key scenes without unwanted color shifts in the highlights? How can you keep shooting without periodic tweaks of Knee and Slope? A growing number of DPs are finding the answers in gamma adjustments, such as Sony’s HyperGamma curves.
Defining gamma
Gamma manipulation is relatively new. Traditionally gamma compensation has been a mandatory and unvarying process in television broadcast cameras. Camera gamma corrects for the nonlinearity of cathode ray tube (CRT) monitors and televisions. If we chart the CRT transfer characteristic of output brightness versus input voltage, we get a curve where output equals input raised to an exponent called gamma. For CRTs, gamma equals 2.2. To compensate, video cameras have always applied a corrective gamma of 1/2.2.
The CRT transfer characteristic (lower curve) is nonlinear. Camera gamma (upper curve) corrects for the nonlinearity. The two curves combine to create a linear system (central line).
Compared to Knee and Slope.
Sony HyperGamma curves teach the old gamma dog some useful new tricks. The curves gently adjust the camera’s gamma characteristic to overcome common exposure challenges. Where conventional Knee and Slope adjustments affect only part of the exposure range, HyperGamma adjusts it all. Knee and Slope can generate color shifts in severe highlights—a tell-tale sign that a project was shot on video. HyperGamma maintains natural color and a more filmic look in the highlights.
Sony HyperGamma holds natural skin tones, even in challenging shots.
Compared to LOG encoding
The S-LOG encoding of Sony’s top CineAlta® cameras can also protect the highlights. But S-LOG results in a relatively flat image that requires a Look Up Table (LUT) for proper monitoring and postproduction. HyperGamma footage can be viewed on any monitor without LUTs.
While the S-LOG image (left) appears flat without a LUT, HyperGamma (right) supports direct, WYSIWYG monitoring.
Four HyperGamma curves
Every Sony CineAlta camera has at least four HyperGamma curves:
HyperGamma 1. Enhanced midtones in low-key areas. Ideal for challenging low-light shots. Compatible with all post processing.
HyperGamma 2. Full dynamic range in high-contrast scenes. An excellent problem solver for exterior day shots. Compatible with all post processing.
HyperGamma 3. Enhanced midtones in low-key areas. Only compatible with post processing that can handle extended 109% digital range.
HyperGamma 4. Full dynamic range in high-contrast scenes. Only compatible with post processing that can handle extended 109% digital range.
Sony has also created a complete tutorial on HyperGamma accompanied by sample video.
The following Sony products offer HyperGamma:
Study this carefully because there will be a 15 minute quiz next period. It will of course be graded on a curve.
Disclosure, to comply with the FTC’s rules 16 CFR Part 255
This article was either written by Sony employees or for Sony by an outside contractor. It is intended for the Sony Channel on ProVideo Coalition, which Sony sponsors.
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Dave:
Yes, the PDW-700 does have HyperGamma. This model inadvertently missed the list, a clear violation of the No Camcorder Left Behind policy. Thanks for catching this. The Tech Guy has updated the post and is appropriately appreciative.
- TSTG
Posted by The Sony Tech Guy on 06/25 at 03:16 PM
Since you’ve included the EX1R and EX3 in your list of HyperGamma carriers (sounds like a communicable disease) I’m assuming that they are known as CineGammas as well? It’s either Standard Gamma or CineGamma with those cameras. I can’t speak to the 350 or the new 320 because I’m too poor to own any of those lovely items.
- Don
Posted by Don Greening on 08/24 at 01:31 PM
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