[Radiance-general] HDRI - Camera Response Curve

[Jack de Valpine]

Hi Axel and Rob,

Thanks for the follow-up.

Axel Jacobs wrote:

>
>>So as to scene, clear sunny sky conditions would be ideal I suppose with
>>a range from shadowed features to direcly illuminated features... Sorry
>>for this next... So how do you use the luminance measure from the
>>reference card to further calibrate the response curve?
>>    
>>
>
>Have a look at
>http://luminance.londonmet.ac.uk/webhdr/calibrate.shtml
>
>In the header of the RGBE image you'll find an exposure value. Multiply
>this with your calibration factor. This CF will be roughly one, but not
>quite.
>
>  
>
Hey this is great! Though I am still not exactly clear what to do with 
the CF if it is other than 1.0? Am I using this multiplier to correct 
the exposure value of the image?

>>In the book (the new one;-) you also indicate that the darkest exposure
>>should have no RGB values greater than ~200 and the lightest no values
>>less than ~20. I could certainly figure out a filter routine with pcomb,
>>however there must be a simple way to do this with ImageMagick. The
>>point being to run a quick preprocess check on the the bounding images.
>>Any takers or suggestions for how to do this easily?
>>    
>>
>
>The netpbm utilities allow you to easily create histograms. I use this in
>WebHDR: For each uploaded image, the histogram is plotted, and the
>exposure value given. Give it a try, if you like.
>
>  
>
Great! I will check it out.

-- 
# Jack de Valpine
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#
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