Hi Matti,  I'm a newbie in radiosity so I think my question is a stupid one.
I can't understand what you really mean with "photograph dynamic range".
Is it referred to the challenge of simulating the human eye dinamic exposure
range? Or is it referred only to the photographic devices simulation? Like
film exposure range, diafragm/time exposure calculation?

Thank you in advance.
bye, save


Matti Karnaattu wrote:
>>I mean the simulation with the radiometry (or photometric) value of
>>a lamp (power, light intensity, or Photometric Solid, etc...).
>
>
>Best way to use POV-Ray light simulation is to multiply light source color
>with real light luminance (cm/m^2). Then set fade_distance using following
>formula:
>
>  sqrt(pi * A) / pi
>
>Real world fade_power is 2. Because POV-Ray doesn't have dynamic range
>compression, this isn't enough. I recommend you to define two adjusting
>variables "Gamma" and "Max_Luminance" to make dynamic range compression.
>Gamma is the gamma used to compress image dynamic range and Max_Luminance
>is the luminance (cd/m^2) where pixel luminance at range 0..1 is "1".
>Max_Luminance controls image brightness. When using these variables you can
>calculate light source color multiplier using formula:
>
>  pow(light_source_luminance / Max_Luminance, Gamma)
>
>And global Fade_Power to *all* light sources by using formula:
>
>  (ln(-exp(-ln(2) * Gamma) + 2) + ln(2) * Gamma) * 2 / ln(3)
>
>To simulate photograph dynamic range compression I think that Gamma should
>be ln(0.5)/ln(0.18) because gray card which reflects 18% of light looks
>half bright.
>Light source color luminance (without multiplier) must be one. Good starting
>value for Max_Luminance is 50. Light source colours luminances without
>multiplier must be one. Example for white light, light color is <1, 1, 1>.
>
>Because you probably want to make other light sources than omnidircetional,
>you need to simulate light distribution using spotlights. If light source
>is flat, use spotlight radius -90 falloff 90 tightness 1 for cosine
>falloff.
>
>I don't recommend to use Jaime's lightsys because it doesn't use physically
>accurate lightning. (Sorry Jaime).
>
>Matti
>

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