[Radiance-general] falsecolor weirdness

Mon, 19 May 2003 21:30:15 -0400

Thanks all for your quick response.

> Cc: [email protected]
> To: [email protected]
> From: Greg Ward <[email protected]>
> Subject: [Radiance-general] Re: falsecolor weirdness
> Reply-To: [email protected]
>
> Hi John,
>
> I hope you aren't doing what I think you might be doing -- trying to
> pick luminance values off the falsecolor output using ximage or
> suchlike.  The falsecolor image has already converted the luminances to
> a "false color" display, and the original luminances are lost in the
> process -- converted to this other (visual) representation.  If you
> want to get point luminance values, you'll need to run ximage on the
> original image, not on the falsecolor output.  (You can have falsecolor
> add point values for the extrema if you like using the -e option.)
>
> -Greg

Well, being the idiot that I am, I was trying to get luminance values 
from the falsecolor output.  I guess that explains why the red always 
read 47.8L.  Evaluating the original image gave me the values I needed. 
  Thanks.

> From: "Lars O. Grobe" <[email protected]>
> To: [email protected]
> Subject: Re: [Radiance-general] falsecolor weirdness
>
>
> Do you want luminance or illuminance? Usually you need 
> illuminance-pictures
> rendered with rpict's -i parameter (if you want to know the amount of 
> light
> that hits the surface).
>
> Good luck, CU, Lars.
>

Though I had purposely done a luminance rendering for today's 
presentation, I will have to do illuminance analysis, so the -i 
parameter is next.

> Subject: Re: [Radiance-general] falsecolor weirdness
> From: Rob Guglielmetti <[email protected]>
> To: [email protected]
> Reply-To: [email protected]
>
>
> Odd that areas in the image that are not red would give higher values.
> Here's what Greg told me to do though:
>
> Run "pextrem -o" on the image.  (Read the manpage for details)  The
> second line of the output is the highest value pixel in the image.
> Take the green value from that second line, multiply it by 179 and use
> that number for the scaling (-s) factor in your falsecolor renderings.
> That should make the red areas in your falsecolor rendering be the
> brightest, and allow the color range to depict the rest of the
> luminance best.  I usually use a logarithmic scale to boot, usually 2
> decades or three.  Hope this helps.
>

I will try that next time around.  Seems like this command will give me 
better control over the dynamic range in the falsecolor image.

John