Colin nous illumina en ce 2008-12-17 20:20 -->
> Christian Froeschlin <chr### [at] chrfrde> wrote:
>> Colin wrote:
>>
>>> So, say for example I put a point
>>> light source above a flat surface. If I render it, I see that it's brightest
>>> directly below the source. At a point some distance away from this centerline,
>>> it is dimmer. What I would like is a metric for how much dimmer it is, as a
>>> function of position. I assume this would be trivial from within the
>>> ray-tracing algorithm; I'm just curious if it's possible from the user end.
>> I think the only way from the user end is to go via the brightness.
>>
>> You can position an orthographic camera to look top down on the
>> plane you are interested in. Using a homogenous texture and suitable
>> light intensity should yield a reasonable intensity image.
>>
>> You need to make sure that the surface is lighted by photons only.
>> This should be the case if the light source is completely blocked
>> by some transparent object which is a photon target.
>>
>> You will wish to adapt the gamma settings to get a linear
>> response curve, use 16-bit output for higher precision, and
>> possibly try HDR output (this is in MegaPOV, there is also
>> HDR support in 3.7b but I'm not sure its also for output?)
>>
>> This should already give you the relative intensities.
>> Converting the pixel intensity to a physical unit may be
>> tricky. For reference, you'd probably need some test lens
>> which directs all photons onto the visible area.
> 
> I can work on referencing it easily using a known light source and photodiode
> and calibrate accordingly (in the "real" world).
> 
> How do I read the brightness into a matrix of integer values corresponding to
> the pixel locations?
> 
> 
> 
How about using the image itself as the matrix? After all, any digital image is 
in fact a matrix of values displayed as an image.
If you output as TGA, you get minimal overhead and can have up to 16 bit per 
channel par pixel.


-- 
Alain
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