playexr lut table and black levels

Hi,

My viewer (mrViewer) uses part of the code used in playexr to create the 
lut table for CTL transforms.  This lut is created in log space, like ( 
as the playexr explains ) :

     //
     // We build a 3D color lookup table by running a set of color
     // samples through a series of CTL transforms.
     //
     // The 3D lookup table covers a range from lutMin to lutMax or
     // NUM_STOPS f-stops above and below 0.18 or MIDDLE_GRAY.  The
     // size of the table is lutN by lutN by lutN samples.
     //
     // In order make the distribution of the samples in the table
     // approximately perceptually uniform, the Cg shaders that use
     // the table perform lookups in "log space":
     // In a Cg shader, the lookup table is represented as a 3D texture.
     // In order to apply the table to a pixel value, the Cg shader takes
     // the logarithm of the pixel value and scales and offsets the result
     // so that lutMin and lutMax map to 0 and 1 respectively.  The scaled
     // value is used to perform a texture lookup and the shader computes
     // e raised to the power of the result of the texture lookup.
     //


Recently, a user, trying to match nuke and with my suggestion, used an 
identity transform as RRT and a linear_to_sRGB function (from the CTL 
utilities) to create an sRGB transform.  To make it clear:


/// Utility -- convert linear value to sRGB
float linear_to_sRGB (float x)
{
     if (x < 0.0)
         return 0.0;
     if (x <= 0.0031308)
        return (12.92 * x);
     else
        return (1.055 * pow (x, 1.0/2.4) - 0.055);
}

The problem the user and I are facing is that the LUT table clamps (and 
raises) the black levels to 0.0182 and makes it not match the sRGB curve 
(black levels) as seen in nuke.

I am wondering if anyone has seen something similar with playexr (or 
your own code) and if someone knows how to address this.  Any code or 
pointers would be highly appreciated.

-- 
Gonzalo Garramuño