[Radiance-general] HDRI - Camera Response Curve

[Axel Jacobs]

Jack,

> It sound like
> perhaps the best thing to do is set the aperture manually and vary the
> exposure time manually as well in order to generate your suggested ~10
> samples. Although doing everything manually involves a lot of
> unnecessary touch of the camera.

In my experience, this is indeed the best thing to do.

> 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.

> 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.

I understand that ImageMagick can also give you histograms.

Cheers

Axel