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I was a bit unhappy with the lighting results in the previous version using
the HDRI light macro I've been working on. The light coming from the sun
wasn't intense enough and the shadows from the sun not strong enough.
Looking into the HDRI I was using, I found that, even though it had fairly
good dynamic range, it still had clipping in the sun area. It doesn't have
much of an effect of the appearance of the HDRI, but it has a very
noticeable impact on the light creation.
The updated image shows the results of my next stage of development,
attempting to recover the clipped areas of HDRIs. The clipped areas cannot
be truly recovered (especially any coloured influence), but at least
attempted at faking the clipped brightness.
The first image shows the original scene, and the second the one with the
rebuilt clipped regions.
-tgq
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Download 'pen2 - waterfront, paris - original.jpg' (105 KB)
Preview of image 'pen2 - waterfront, paris - original.jpg'
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To illustrate the effectiveness of my new addition, I did some sample
renders using an HDRI that had a full dynamic range.
The 1st column shows scenes rendered with the original, full range HDRI,
strong shadows from the sun are noticeable and prevalent.
The 2nd column shows the same scenes with a clipped version of the original
HDRI, the scene lighting can be seen to be more uniform due to the clipping
of the suns brightness, and the hard shadows are lost.
The 3rd column shows the scenes using the clipped version of the HDRI, but
with the clipped areas 'rebuilt'. The shadows from the sun can be seen to
return. The result is very similar to the original, but close
investigation shows slight differences due to the estimation process and
information that was lost from the clipping that cannot be recovered (eg,
clipping effectively makes the clipped clours white, losing any colour
information and the rate of brightness increase across the clipped area).
Also, the true maximum brightness in the clipped area can only be assumed
and the parameters tweaked until the result looks 'right'. In this test
the orignal was able to serve as a reference, and used to achieve a
convincing effect.
-tgq
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Attachments:
Download 'rebuild.jpg' (445 KB)
Preview of image 'rebuild.jpg'
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