Hi Chris,
If you haven't passed the picture through pfilt or otherwise introduced an exposure change, then it would be much faster to use pcompos to extract the value you're interested in. E.g.:
pcompos -x 1 -y 1 rendered_image.hdr -Xpos -Ypos | pvalue -h -H -d
If getinfo shows one or more EXPOSURE= lines in the header, then the above won't quite work and you'll need to use pvalue. The syntax for the command you want is:
pvalue -o -h -H rendered_image.hdr | rcalc -e 'eq(a,b):if(a-b+.5,b-a+.5,-1);and(a,b):if(a,b,a)' \
-e 'cond=and(eq($1,x_location),eq($2,y_location))' -e '$1=$3;$2=$4;$3=$5'
Nasty, eh? It's also slow. Use pcompos if you can. A faster alternative to the above is to use sed:
pvalue -o -h -H rendered_image.hdr | sed -n 's/^ *x_location *y_location //p'
Cheers,
-Greg
···
From: Chris Humann <[email protected]>
Date: April 5, 2010 4:35:52 PM MDTMy apologies for not being more specific when posting earlier. I also just realized that I missed a similar post in the archives from May 2008. However, the latter posts don't quite answer the question at hand.
I have a series of images produced from a script in which the previous image octree is over written prior to the proceeding rpict call. Given the latter condition, I don't think vwrays connected to rtrace will work as I don't have the corresponding 'octree' file.
I suppose I could write a Python Script to parse the pixel location and its associated value, but that seems a bit over kill for what seems should be a straight forward, one line task.I'm trying to use 'pvalue' to calculate a pixel value at a specific x,y location in an image by piping 'pvalue' through 'rcalc', and am stuck on the correct syntax to use for the expression, '-e', in 'rcalc':
pvalue -o -h -H rendered_image.hdr | rcalc -e '(x_location,y_location
Thanks again.
Chris