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Clipka wrote:
> >> 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 light at the top is clipped by exposure on the CCD I believe. The correct
adjustment is probably to linearly increase the brightness till the light hit
the ceiling for a non-HDR image format (e.g. 255 in people 8 bit minds, although
of course you posted a 16 bit PNG).
I converted the original OpenEXR image to a 16 bit image in linear space, and
did the adjustments, then adjusted the gamma 1.0 image you posted (after
converting it to linear space again) to match the brightness, and finally saved
them both as an sRGB JPEG.
Looks about perfect to me.
> > 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.
Oh, I see what you mean. Photoshop was doing the right thing; I should just
learn to trust the 'shop.
Cheers,
Edouard.
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