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Old May 4th, 2003, 04:57 PM   #1
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dynamic range

I recently learned a new video term "dynamic range". It refers to the range of brightnesses a chip can handle at the same time.
One of the new JVC professional models has an ad on the JVC website showing a couple standing next to a window. They look great but the scene outside the window is totally washed out because of low dynamic range. They then show their camcorder's high (400%) dynamic range with which both the people and the scene outside are nicely exposed. It seems that JVC uses a logarithmic algorithm to lessen the effect of a wide range of incoming light.
My question is does anyone know if a consumer-priced camcorder offers a similar feature (Maybe the XL-2!).Alternatively is anyone aware of a logarithmic special effect that can be applied in post?

Steve Siegel

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Old May 4th, 2003, 05:20 PM   #2
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It has to pretty much be applied at the camera head end. If no detail is recorded (because of blown highlights) then no amount of post processing is going to bring it back. Cameras in the prosumer price range typically don't have that type of processing capabilities.
Jeff Donald
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Old May 4th, 2003, 05:26 PM   #3
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While Jeff is correct, there are a number of processing algorithm strategies for dynamic range compression, notably those in the gradient domain, which can have the overall effect of balancing out whatever recoverable (i.e., unclipped) luminance values exist in a digital image.

Here's one good recent paper on gradient domain dynamic range compression.

See also Paul Debevec's web site for a lot of fun research dealing with High Dynamic Range image acquisition and manipulation, including a free download of HDRShop, which has, to my knowledge, at least one of the compression methods implemented as an available plug-in.

I hesitate to add this because it may be obvious, but simply futzing with the gamma curve--the function that determines how digital pixel values are mapped to their actual display brightnesses--can often help to bring out detail.

Of course, the development of higher dynamic range CCDs (or other image acquisition solutions) will go a long way towards making video more like film.

On a related note, The SONY CineAlta 24P cameras have some sort of processing scheme that claims to recover one bit of dynamic range per channel beyond what the CCDs and A/D are capable of. I once requested a white paper from SONY to get the details on this but I never received a response. Maybe somebody else on DVInfo.net has had more luck.
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Robert K S

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Old May 4th, 2003, 05:44 PM   #4
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...Steve, you should e-mail Chris Hurd to change your screen name to your real name.
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