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Re: [Openexr-devel] Cineon -> half conversion?

From: Ken McGaugh
Subject: Re: [Openexr-devel] Cineon -> half conversion?
Date: Wed, 02 Mar 2005 15:32:33 +0000
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20040914

Paul Miller wrote:

Note that nowhere is there any reference to "black" or "white".
>> They are video concepts and should only be used when preparing
>> pixel values for display.

I like this a lot. I don't suppose adding display controls for black and white would essentially just drive a scale/bias in the HDR shader?

Correct.  I think the simplest and most general purpose display controls
vor a commercial app are

    blackPoint   (usually near 0.0)
    whitePoint   (usually near 1.0)
    gamma        (usually between 1.5 and 2.5)
    softClip     (usually between 0.0 and 0.4)

These are then used in the following way:

    1. Remap using black-point and white-point.

    2. Apply gamma correction.

           x = pow( x, 1.0/gamma );

    3. Apply soft clip using the following function.

          float softClip( float x, float s )
              float b = 1.0 - s;
              if ( x > b )
                  x = b + (1.0 - exp(-(x-b)/s))*s;
              return x;

If you convert a cineon using the method described previously, and then display
with these controls set to

    blackPoint = 0.008
    whitePoint = 1.008
    gamma      = 1.53
    softClip   = 0.4

you will see an image that resembles the classic Kodak recommended log->video 

Note that this is what 3D-Equalizer does (at our request).


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