Am 22.12.2010 22:06, schrieb Edouard:
> Warp<war### [at] tagpovrayorg>  wrote:
>> On 12/22/2010 09:58 AM, Thomas de Groot wrote:
>>> Idem for me as for Kenneth, also in Firefox. It is not the white background.
>>> Even the ceiling light in POV-Ray is pure white, compared to muddy grey in
>>> the photograph.
>>
>>    There indeed seems to be something wrong with the original photograph,
>> as posted. One would indeed assume the ceiling light should be pure
>> white in the image (I'm assuming in the original HDRI image it's "whiter
>> than white").
>>
>>    Exactly what kind of adjustment was made to the original data in order
>> to get the posted "photograph"?

The original image was much dimmer (half the physical brightness as the 
PNG I posted). I guess the dim overhead light is due to reaching the 
CCD's dynamic range limit, and the image was linearly adjusted in 
brightness to represent absolute light intensity in some nice SI unit.

> The original was taken with a CCD, so the captured response is linear. Taking
> the 600nm OpenEXR version and converting it to a 2.2 gamma gives a realistic
> image to my eyes. If the original was a photograph, then you'd have a non-linear
> tone curve to deal with (exponential, but with rolloff on the top and bottom)

The original is an OpenEXR, and therefore by definition linear. A proper 
image viewer should do the gamma adjustment for your display 
automatically, so you shouldn't do any manual gamma correction on the 
image, otherwise you'll just screw it up.

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