[Radiance-general] macbeth gamut and coordinates

[Greg Ward]

> From: genevieve lucet <lucet@servidor.unam.mx>
> Date: December 16, 2003 1:46:53 PM PST
>
> I need to correct the color of mural painting photographs and I am 
> trying to do it using macbethcal. I observe that several colors are 
> out of gamut  (diagonal lines are visible). When I apply macbethcal to 
> the image (macbeth_spec.pic( that is included with radiance,  the 
> yellow square shows the same problem.
> Is it only a display problem or does it involve the calculation of the 
> colors?

When colors are shown as "out of gamut" by macbethcal, it simply means 
that they fell outside of what macbethcal decides is the capture 
systems color gamut.  These colors are then ignored.  If macbethcal 
warns about "moderate colors out of gamut," it may be that the input 
color space is not behaving as expected, and the results may not be 
quite right.

> The chart has rounded corner. This is why I would prefer to put the 
> coordinates of the color squares instead of the coordinates of the 
> chart. Does it matter?

It doesn't matter much, as there is a bit of leeway in selecting the 
patches, but macbethcal expects you to give the corners of the color 
patches rather than the chart itself.

> This part is not a radiance problem but if somebody can help, .. I am 
> looking for a software to correct the distortion of these images to 
> obtain orthophotos of these paintings.

Photoshop has a perspective warp feature that may be used for this.

-Greg