[HDRI] Relationship - Outdoor illumination value, HDR pixel value, ISO, Shutter Speed and fstop

[Lars O. Grobe]

Hi,

what you want is a HDR image that contains pixel values in photometric
units. To achieve this generate a reasonable response curve, which
compensates for the non-linear response of the sensor to illuminance on
each channel. Second, you should compare the luminance from the pixels
to a reference. One way to do so is using a stabilized light source.
This will give you a factor that can be used as a multiplier to get from
the pixel values to cd/m2.

Besides that, aperture size, focus distance, the lens etc. all have
influence on the pixel values in your image...

Cheers, Lars.
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