Re: Ambient correction
Re: Ambient correction
- Subject: Re: Ambient correction
- From: Graeme Gill <email@hidden>
- Date: Tue, 22 Apr 2008 16:06:56 +1000
email@hidden wrote:
All major display calibrator vendors (all two of us) are offering
some form of
ambient correction.
Maybe a bit OT but it would be useful to discuss this more.
I think that it is a matter of intent. First let me say, I do not
believe that Scotopic adaptation is an issue here. I think that it has
more to do with small/field vs large field viewing conditions
As far as I understand it, it's about the different viewing environments
used in original image capture, and display on monitors.
In TV, the original image is usually captured in a brightly lit environment.
The reproduction is then (typically) viewed in a quite dark environment.
For the images to appear to be the same, the lightness scale has to be altered.
This is done in TV by having a gamma encoding of 2.2 in the camera, and
gamma decoding in the CRT tube of 2.5, increasing the contrast.
The "standard" used for TV talks about having a standard gamma of (about) 2.2,
although it doesn't mention the re-rendering implicit in the display.
So when you're calibrating a computer monitor to display Video,
it's in fact wrong to calibrate it to gamma 2.2 (or REC 709,
or possibly sRGB), you should instead be calibrating it to gamma 2.5.
Or you should be explicitly applying a rendering intent to
compensate for the different viewing environment, possibly calling
this "Ambient Correction".
It's basically the same stuff that happens in color profiles if
you are applying appearance models to compensate for different
viewing conditions.
Graeme Gill.
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