[Radiance-general] pvalue output

[Greg Ward]

Hi Kyle,

You have the conversion factor (179) correct, and the coordinate  
translation *almost* correct -- you actually have to subtract the y  
value from ymax-1 (rather than ymax) to get the exact coordinate.

Hope this helps.
-Greg

> From: kkonis at berkeley.edu
> Date: August 16, 2008 7:51:45 PM PDT
>
> Hello all,
>
> I am looking at the output from
>
> pvalue -o -b A.hdr > test.txt
>
> and checking to see if the luminance from the pvalue output for a  
> given
> pixel matches the luminance for the same pixel when clicked on in
> Photosphere. (I am doing this to create a powerpoint slide that
> illustrates that luminance can be extracted from each pixel in a  
> radiance
> image for a very general audience).
>
> (Actually i click a pixel on the image in Photosphere and then  
> track down
> it's record in the pvalue output)
>
> I noticed that the 0,0 Origin in Photosphere is the upper left  
> corner, and
> for Radiance images it is the lower left (i believe ? ).
>
> Since my image is 1536 x 1536 pixels, pixel x=256,y=550 in  
> Photosphere is
> then row:
>
> x=256, y=abs(550 - 1536), brightness.value
>
>  . . . . as output from Pvalue.
>
> I take brightness.value*179 to get my pixel luminance and it matches
> closely with the output from Photosphere, but not exactly. I want  
> to ask
> if I am using the correct conversion from pvalue's output to  
> luminance,
> and that my understanding of the (0,0) origin locations in Radiance  
> and
> Photosphere is correct.
>
>
> I'm a relatively new user so any help would be appreciated!
>
> Kyle