[HDRI] calibrating HDR pictures with real world luminance

[Mehlika Inanici]

Hi,

You may want to look at the validation study at:
Inanici MN. “Evaluation of High Dynamic Range Photography as a Luminance Measurement Technique”, Journal of Lighting Research and Technology, Vol. 38, no. 2, June 2006, pp. 123-136.

Another version of this study is available at:
http://repositories.cdlib.org/lbnl/LBNL-57545/

This study evaluates Photosphere rather than HDRShop, but you can find information regarding your first 3 questions.

Hope this helps... Regards,
Mehlika

On Tue, 26 Sep 2006, Pierre-Felix Breton wrote:

> Hi!
>
> I am experimenting with HDR images and a luminance meter to see how tone
> mappers can actually help reproducing human perception.
>
> Here is what I  am currently  doing:
>
> a)capture a serie of LDR images using a Canon Rebel XT, only changing the
> shutter speed, with constant Fstop,  saved as JPG with sRGB profile
> b)creating a calibration curve in HDR Shop
> c)measuring a few points in cd/m2 with a luminance meter (LS-110)
> d)making an HDR image out of the LDR images using the calibration curve
> e)experimenting different tone mappers available on the DVD of the HDRI book
> from our favorite well known HDRI gurus.
>
> Here are a few questions that puzzles me still:
>
> 1)  I am trying to scale my HDR image to the measured physical  values.  I
> found somewhere that luminance = 179 * (R*0.265 + G*0.067 + B*0.065).  Can I
> assume that this equation is the one to use to scale my HDR file properly?
>
> 2) In some references, it is mentionned that I should always capture LDRs
> with a Daylight white balance.  Is this the general agreement?  Even if my
> scene is lit with tungsten lights?
>
> 3)I found limited explanation on how the camera calibration curve would
> affect the results in HDR Shop.  I would have to think  that this is to
> linearize the color values (remove the effect of Gamma + CMOS response) so
> luminance measurements can be actually applied to the colors later on.
>
> 4)HDR Shops refers to Fstops in the UI.  However,  I read that you want to
> maintain Fstops constant and only change the shutter speed.  The problem I
> have is that the interpreted Fstops of HDR Shop turn into some "arbitrary"
> numbers and I can't really type-in the values used by my camera.
>
> I am not too sure if I am using the right methods.   Some "cook  book" would
> be handy.
>
> Best regards,
>
> Pierre-Félix Breton
> www.pfbreton.com <http://www.pfbreton.com/>
>
>
>
>