[HDRI] Re: extraction of luminance values

[Gregory J. Ward]

Hi Nick,

Most people use a false color representation to look at luminance  
values.  Assuming you have Radiance installed, the command looks like  
so:

	% falsecolor -i render.pic -s auto \
		| ra_tiff -z - render_fc.tif

If you have Photosphere, you can use the Command-N sequence to get a  
false color display.  Regrettably, it won't save out with the legend  
(scale).

If you want to look at the values directly, the pvalue command will  
give you radiances, which you can convert to luminance using the  
appropriate efficacy value, e.g.:

	% pvalue -h -H -b render.pic \
		| rcalc -e '$1=$1;$2=$2;$3=179*$3'

The first and second columns in the output are the x and y pixel  
positions, measured from the lower-left corner of the image.

I was curious to see what a 3-D rendering would look like, so I used  
the command:

	% pvalue -h -H -b -d render.pic \
		| gensurf void picsurf t s - 254 172 -o \
		| obj2mesh > render.rtm

The 254 and 172 values are the horizontal and vertical dimensions of  
my example image, respectively.  I then used objview to render the  
following Radiance file:

void plastic grey
0
0
5 .5 .5 .5 0 0

grey mesh picsurf
1 picsurf.rtm
0
0

-----------
This produced a rather bland result, so I added a pattern  
corresponding to the output of falsecolor:

void colorpict colorful
7 red green blue electric_x1y1fc.pic . 1.47398844*Py 1-Px
0
0

colorful plastic colored
0
0
5 .5 .5 .5 0 0

colored mesh picsurf
1 picsurf.rtm
0
0

The 1.47398844 value is 254/172, as needed to fit the image into my  
square area.  In retrospect, I probably should have used a wider base  
in the gensurf command to get a rectangular plot.  I can send anyone  
who wants to see the images I generated.

-Greg

> From: panick <panickece at gmail.com>
> Date: August 17, 2007 9:52:05 AM PDT
>
> Hello all,
>
> 1.How can I extract results of luminance from a .pic file that I  
> have already rendered using a grid of points?
> (Because the rendering process lasts 2-3 hours)
>
> 2.Is there any command that gives a 3D presentation of the values  
> of a grid?
>
> Thanks,
>
> Nick