Dear Group,
I have two pictures of a same scene, but they illuminated with two different lights.
I want to post the value of illuminance pixel (intentity of pixel) on the same point in the two pictures.
I tested with the program of ximage and falsecolor, but it is not a recise method, because I cannot select
the same point using the cursor.
can you say to me what's the good way to do this?
Thank you, Djafi
···
---------------------------------
Do You Yahoo!? -- Une adresse @yahoo.fr gratuite et en fran�ais !
Testez le nouveau Yahoo! Mail
Hi Djafi,
There are a few ways to do this. Probably what you really want to do is get the illuminance at some point on the work plane. To do this you should check out the "rtrace" command (man rtrace). This enables you to essentially measure at given locations in the scene. The command take some of the same parameters as does rpict, although you will find that you should increase certain ambient parameters (ab, ad, as, ar, aa) in order to obtain more accurate measures. I would also suggest (as would many others on this list I suspect) that you use rtrace to obtain measures for multiple points on the workplane so you have a better sense of how results are working out and comparing between scenarios.
As an alternative to this, if you really want to do image processing (ie pixel comparisons/calculations) then it would be possible to use "pvalue" to get the values at specific pixels in the images.
Just as a side note, you have indicated that you are interested in illuminance values, to obtain illuminance you must be sure to render (rpict) or sample (rtrace) using the -i switch to obtain irradiance values.
-Jack
Faouzi Djafi wrote:
···
Dear Group,
I have two pictures of a same scene, but they illuminated with two different lights.
I want to post the value of illuminance pixel (intentity of pixel) on the same point in the two pictures.
I tested with the program of ximage and falsecolor, but it is not a recise method, because I cannot select
the same point using the cursor.
can you say to me what's the good way to do this?
Thank you, Djafi
------------------------------------------------------------------------
Do You Yahoo!? -- Une adresse @yahoo.fr gratuite et en français !
Testez le nouveau Yahoo! Mail <http://fr.mail.yahoo.com>
--
# John E. de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction
Faouzi Djafi wrote:
I want to post the value of illuminance pixel (intentity of pixel) on the same point in the two pictures.
can you say to me what's the good way to do this?
The program rtrace can compute illuminance at a specific point; this is typically what I use when I want to compare scenarios or capture daylighting data for a space. You can feed rtrace a text file with a whole series of points (one per line) and it will calculate the illuminance for each one in turn.
For example, create a file with lines like this:
0 0 0 0 0 1
0 0 10 0 0 -1
That file describes two "virtual light meters", one on the floor at 0,0,0 looking up. The other is located ten units above it, looking down, just as an example. You'd feed these to rtrace like this:
rtrace [options] -I scene.oct < points.txt > values.txt
points.txt is the file with all your points you'd like to evaluate, and then rtrace saves the computed illuminance values in values.txt.
Of course, you'd then have to manually paste in some sort of graphic tag indicating the illuminance into a completed .pic file, if you wish to have an image with the illuminance. I'm sure there's a way to have Radiance do it for you, but in general I use rtrace to spit out a whole series of numbers, which I summarize in tabular form. I'll usually just do one image which serves as a reference key to all the calculation points. This method works for me; YMMV.
···
----
Rob Guglielmetti
e. [email protected]
w. www.rumblestrip.org
Oops, Jack already replied. Thanks Jack! One minor nit though...
Jack de Valpine wrote:
Just as a side note, you have indicated that you are interested in illuminance values, to obtain illuminance you must be sure to render (rpict) or sample (rtrace) using the -i switch to obtain irradiance values.
Actually, you use -i in rpict, but -I in rtrace, for illuminance.
-RPG
Ack. Thanks Rob! I knew I was writing too quickly.
-I is for irradiance at specific sample points
-i would be for irradiance of specific rays
-Jack
Rob Guglielmetti wrote:
···
Oops, Jack already replied. Thanks Jack! One minor nit though...
Jack de Valpine wrote:
Just as a side note, you have indicated that you are interested in illuminance values, to obtain illuminance you must be sure to render (rpict) or sample (rtrace) using the -i switch to obtain irradiance values.
Actually, you use -i in rpict, but -I in rtrace, for illuminance.
-RPG
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
.
--
# John E. de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction