[Radiance-general] Intentity_of_pixel

Mon, 15 Dec 2003 12:29:17 -0500

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Hi Djafi,

There are a few ways to do this. Probably what you really want to do is=20
get the illuminance at some point on the work plane. To do this you=20
should check out the "rtrace" command (man rtrace). This enables you to=20
essentially measure at given locations in the scene. The command take=20
some of the same parameters as does rpict, although you will find that=20
you should increase certain ambient parameters (ab, ad, as, ar, aa) in=20
order to obtain more accurate measures. I would also suggest (as would=20
many others on this list I suspect) that you use rtrace to obtain=20
measures for multiple points on the workplane so you have a better sense=20
of how results are working out and comparing between scenarios.

As an alternative to this, if you really want to do image processing (ie=20
pixel comparisons/calculations) then it would be possible to use=20
"pvalue" to get the values at specific pixels in the images.

Just as a side note, you have indicated that you are interested in=20
illuminance values, to obtain illuminance you must be sure to render=20
(rpict) or sample (rtrace) using the -i switch to obtain irradiance value=
s.

-Jack

Faouzi Djafi wrote:

> Dear Group,
>
> =20
>
> I have two pictures of a same scene, but they illuminated with two=20
> different lights.
>
> I want to post the value of illuminance pixel (intentity of pixel) on=20
> the same point in the two pictures.
>
> I tested with the program of ximage and falsecolor, but it is not a=20
> 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?
>
> =20
>
> Thank you, Djafi
>
>
> -----------------------------------------------------------------------=
-
> Do You Yahoo!? -- Une adresse @yahoo.fr gratuite et en fran=E7ais !
> Testez le nouveau Yahoo! Mail <http://fr.mail.yahoo.com>=20

--=20
#	John E. de Valpine
#	president
#
#	visarc incorporated
#	http://www.visarc.com
#
#	channeling technology for superior design and construction

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Hi Djafi,<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
-Jack<br>
<br>
Faouzi Djafi wrote:<br>
<blockquote type="cite"
 cite="[email protected]">
  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';">Dear Group,</span></p>

  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';"><o:p></o:p></span>&nbsp;</p>

  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';">I have two pictures
of a same scene, but they illuminated with two different lights.<o:p></o:p></span></p>

  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';">I want to post the
value of illuminance pixel (intentity of pixel) on the same point in the
two pictures.<o:p></o:p></span></p>

  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';">I tested with the program
of ximage and falsecolor, but it is not a recise method, because I cannot
select<o:p></o:p></span></p>

  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';">the same point using
the cursor.<o:p></o:p></span></p>

  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';">can you say to me what's
the good way to do this?</span></p>

  <p class="MsoNormal" style="margin: 0cm 0cm 0pt;"><span
 style="font-size: 10pt; font-family: 'Courier New';"><o:p></o:p></span>&nbsp;</p>

Thank you, Djafi<o:p></o:p>
 
 
 <hr size="1">Do You Yahoo!? -- Une adresse
@yahoo.fr gratuite et en fran&ccedil;ais ! 
 <a href="http://fr.mail.yahoo.com">Testez le nouveau Yahoo! Mail</a> 
</blockquote>
 
<pre class="moz-signature" cols="$mailwrapcol">-- 
#	John E. de Valpine
#	president
#
#	visarc incorporated
#	<a class="moz-txt-link-freetext" href="http://www.visarc.com">http://www.visarc.com</a>
#
#	channeling technology for superior design and construction</pre>
 
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