[Radiance-general] vta 2 vth

[Mehlika Inanici]

Hi Lars,

Yes, I would like to change the projection of the existing image from an 
equi-angular to hemispherical fisheye, if that is doable. But my 
intention was similar to your motive. I have used hemisherical fisheye 
images in the past to calculate illuminance at the camera point 
(averaging luminance within the circular area and multiplying by pi). 
Since the physical fisheye lenses have equi-angular (or equi distant) 
projections (not cosine corrected hemispherical fisheye projections), I 
am trying to calculate illuminance from a HDR photograph taken with a 
fisheye lens.

Thanks,
Mehlika

Lars O. Grobe wrote:
> Hi Mehlika,
>
> what exactly do you want to achieve? The command you quoted from Greg's
> mail does not change the projection (or view-type). It corrects for the
> weigth of luminances according to their angle from the optical axis (or
> the view-direction of the sensor) when contributing to the illuminance
> of a point, which is also known as the cosine law. So you can expect a
> fall-off. Do you want to change the projection of an existing image?
>
> Lars.
>
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