"Allen" <nomail@nomail> wrote:
> Okay,
> It's been plaguing me.... what is HDR and what program uses HDR?

From a response I gave previously on this:
(http://news.povray.org/povray.advanced-users/message/%3Cweb.44eef0ad8da26955c150d4c10%40news.povray.org%3E/#%3Cweb.44e
ef0ad8da26955c150d4c10%40news.povray.org%3E)

"When most image types are written/displayed, the coulour values range from
0
to 1. However, in real life, light brightness is by no means limited to 1
(i.e., compare the sun to a light bulb to a white piece of paper), in fact
it can be substantially more, relatively speaking.  So when photos (or
equally, rendered images are written, the colour of superbright objects get
clipped at 1 because of the image file limitations and the true brightness
of the scene gets lost.  This is generally fine for an image meant for
direct viewing, however, if we want to use the image for something where
the brightness is required (e.g. reflection maps, environment lighting,
or,as you want to do, scene lighting evaluation) then we end up getting
false results, because the true brightness of the +1 pixels is lost and
they are treated the same as pixels with an actual value of 1 (i.e., in the
image sun, the light bulb and the white piece of paper will all be treated
as having the same brightness even though this is clearly untrue).  HDR
(called high-dynamic range as opposed to LDR or low-dynamic range) and some
other format save pixel values as floating point numbers and can save the
actual value of each pixel,no matter what the value, thus preserving the
true brightness or dynamic range of the image. Unfortuneatley POVRay 3.6
does not support HDR (it is being implemented in the 3.7 beta however) but
megaPOV does (http://megapov.inetart.net/).

I hope this has been more helpful than confusing.  If you have any more
questions or want to see some examples of how it can work, feel free to
ask.  Also,have a look at this page, as it has some good information and
illustrations of HDR vs LDR:
http://www.highpoly3d.com/writer/tutorials/hdri/hdri.htm"

Further:
HDR is just an image file format, it just contains additional information
(ie, brightness exponent) compared to jpg, bmp, etc.  So any program that
can read images could be modified to read and use HDR images (as the
current both megaPOV and the POV 3.7 betas have).  There is a lot of
information and resources on this topic if you want to search more.

-tgq

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