[Radiance-general] Re: falsecolor weirdness

[Rob Guglielmetti]

On Monday, May 19, 2003, at 01:50 AM, Greg Ward wrote:

> 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.)

John, my previous email was probably misleading.  Listen To Greg, which 
is always good advice.  Another way to look at things is this:  think 
of a raw, unfiltered image fresh from rpict as a collection of 
"intelligent pixels".  That is, the value of each pixel is the radiance 
of that point, as you know.  But any *filtered* version of that image, 
while still containing that depth of information about each pixel, has 
been filtered, so the info no longer has any basis in reality.  I 
learned this rather quickly when I tried doing a falsecolor image of an 
image that had already been filtered with pcond -h.  Oops.  It's a good 
argument for always saving the original image, as you never know when 
you might want to extract more info from the image in the form of a 
falsecolor, or whatever.

Rob Guglielmetti
rpg@rumblestrip.org
www.rumblestrip.org