Finding the difference between illuminance at two points in a .pic

Hello Radiance users!

I have an interesting dilemma. I want to find the total difference in illuminance values between two .pic files, summed for each point in the .pic.

Basically, this would allow me to take two .pic files and fingure out the total difference in illuminance between the two scenes. Of course, the two .pic files are the same view of the same scene, only the source and reflectance characteristics are changing.

It should be noted that I'm looking for a way to calculate a single value for the whole .pic, not a difference image or something of that sort.

Thanks for any help you can offer!

- Matt Brugman

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Hi Matt,

Try this:

  rlam -if '!pvalue -h -H -b -df input1.pic' '!pvalue -h -H -b -df input2.pic' \
    > rcalc -if2 -of '$1=$1-$2' | total -if -m

This should work with any recent Radiance release. Older releases don't support the binary options, so you'll need the slower version:

  rlam '!pvalue -h -H -b -d input1.pic' '!pvalue -h -H -b -d input2.pic' \
    > rcalc '$1=$1-$2' | total -m

You may need to escape the '!' in the above commands if you use the C-shell, which claims this as its history character.

Note I've added the -m option to each of the total commands. This computes the "average difference" between pixels, rather than the sum. I don't know what the sum would mean, which is why I added -m.

-Greg

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From: "M. Brugman" <[email protected]>
Date: December 15, 2008 4:23:12 PM PST

Hello Radiance users!

I have an interesting dilemma. I want to find the total difference in illuminance values between two .pic files, summed for each point in the .pic.

Basically, this would allow me to take two .pic files and fingure out the total difference in illuminance between the two scenes. Of course, the two .pic files are the same view of the same scene, only the source and reflectance characteristics are changing.

It should be noted that I'm looking for a way to calculate a single value for the whole .pic, not a difference image or something of that sort.

Thanks for any help you can offer!

- Matt Brugman