Hello Everyone,
I would like to know if there is any specific way to find the reflectance of red, green and blue in order to obtain a specific color desired.
Secondly is there any library of materials to choose from ..?
Thank you
GV,
This website can help you pick a colour:
http://www.luxal.eu/resources/radiance/cp4r.shtml
I don't know of a library of specific materials... but if there's one
I'd definitely like to know about it.
N.
···
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of G V
DEEPAK
Sent: Wednesday, November 05, 2008 11:14 AM
To: Radiance general discussion
Subject: [Radiance-general] Color reflectance values and materials..
Hello Everyone,
I would like to know if there is any specific way to find the
reflectance of red, green and blue in order to obtain a specific
color desired.
Secondly is there any library of materials to choose from ..?
Thank you
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
I don't know of a library of specific materials... but if there's one
I'd definitely like to know about it.
There is one small library file distributed with radiance (materials.rad), and there are some on the radsite ftp server.
Still - in most cases you will not be able to use generic material values but need information from a specific sample!
CU Lars.
G V DEEPAK yazmış:
Hello Everyone,
I would like to know if there is any specific way to find the reflectance of red, green and blue in order to obtain a specific color desired.
Secondly is there any library of materials to choose from ..?
Hi,
there are several ways, most of them described in Detail in the book "Rendering with Radiance" which dedicates one chapter to the topic. There are more or less three ways, first guess and compare, second calibrated exposures, third specialized measurement devices. The choice depends on both required accuracy (in many applications, the overall brightness is much more important then color) and, of course, budget 
CU Lars.
I would like to know if there is any specific way to find the reflectance of red, green and blue in order to obtain a specific color desired.
If you've got a sample of the color, sure--you do colorimetry and convert the values from the colorimeter's color space to the Radiance color space. It takes some care to choose the sample, however.
Secondly is there any library of materials to choose from ..?
We wish! Developing one, or tools to generate them from other data is a project that so far has not been addressed.
Randolph
Anyway, as a start it might be worth thinking about a central web based material depository where we all can share our own creations. The display format can be a simple list with mat, cal, pic files and a little preview.
Anyone interested in starting that?
Maybe one should first consider a database of measured values. Based on this, one could implement a material editor that could query that database and give a radiance material definition as a result. The advantage is that I could compile the material data available into a description fitting the needs of my specific application. It is important to keep in mind that our measurements and simulations not only have a degree of accuracy but also a scale. A material for a wall of bricks is not only depending on exterior influences (dirt, humidity, vegetation) but also on the scale we look at it - from far a way it will be sufficient to define it as one uniform color, sampled e.g. over 2mx2m, from a close point of view I would want to have a brick texture including the different colors of brick and mortar, and for a detail view I would need the color and structure of only the brick itself, as the mortar would be a different material. Just one very simple example, other materials are much more difficult. Still sharing the measured values (including very detailed descriptions of object and set-up) would be very useful for the secondary materials, those that a simulation not really focuses on and could be approximated. Think I would be interested in contributing.
CU Lars.
Sorry about the messed-up subject line in my last post...
···
---------- Forwarded message ----------
From: Axel Jacobs <[email protected]>
Date: 2008/11/6
Subject: Re: Radiance-general Digest, Vol 57, Issue 4
To: [email protected]
Erwin,
Anyway, as a start it might be worth thinking about a central web based material depository where we all can share our own creations. The display format can be a simple list with mat, cal, pic files and a little preview.
Anyone interested in starting that?
There is a site in Japan doing something rather similar:
http://arch.xtr.jp/radiance/mat_database.htm
Just pipe it through an on-line translator. There are a handful of
different pages. It seems that all examples are from freely available
example models and mailing list posts.
Axel
Hi,
Another resource is:
The focus is on paint colors. But they supply all kinds of color values including XYZ.
-Jack
Axel Jacobs wrote:
···
Sorry about the messed-up subject line in my last post...
---------- Forwarded message ----------
From: Axel Jacobs <[email protected]>
Date: 2008/11/6
Subject: Re: Radiance-general Digest, Vol 57, Issue 4
To: [email protected]Erwin,
Anyway, as a start it might be worth thinking about a central web based material depository where we all can share our own creations. The display format can be a simple list with mat, cal, pic files and a little preview.
Anyone interested in starting that?
There is a site in Japan doing something rather similar:
http://arch.xtr.jp/radiance/mat_database.htm
Just pipe it through an on-line translator. There are a handful of
different pages. It seems that all examples are from freely available
example models and mailing list posts.Axel
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
--
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction
Jack,
Forgive my ignorance on the topic, but how do you convert those values to something that looks right in Radiance? I've tried just using RGB values like the ones from the site, but everything is simply too bright. And scaling them down uniformly seems to change the hue.
Mark
···
On Thu, 6 Nov 2008, Jack de Valpine wrote:
Hi,
Another resource is:
The focus is on paint colors. But they supply all kinds of color values including XYZ.
-Jack
Axel Jacobs wrote:
Sorry about the messed-up subject line in my last post...
---------- Forwarded message ----------
From: Axel Jacobs <[email protected]>
Date: 2008/11/6
Subject: Re: Radiance-general Digest, Vol 57, Issue 4
To: [email protected]Erwin,
Anyway, as a start it might be worth thinking about a central web based material depository where we all can share our own creations. The display format can be a simple list with mat, cal, pic files and a little preview.
Anyone interested in starting that?There is a site in Japan doing something rather similar:
http://arch.xtr.jp/radiance/mat_database.htm
Just pipe it through an on-line translator. There are a handful of
different pages. It seems that all examples are from freely available
example models and mailing list posts.Axel
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general--
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction
Mark,
That's where gamma values come in. Let's say the RGB values of a paint
sample from EasyRGB are (125,150,175), a blue gray. Take each channel,
divide by 256, take the result to the power of 2.2 (monitor gamma) and
then multiply by 256.
R = (125/256)^2.2 * 256 = 52.9
G = (150/256)^2.2 * 256 = 79.0
B = (175/256)^2.2 * 256 = 110.9
If you put the resulting values (52.9,79.0,110.9) in as the R G and B
material colors, you should get the correct paint color in your
simulation that matches the physical paint color.
--Dave
Hi Dave,
As Mark already said, these values seem very bright to me also.
Once I did some measurements on a Kodak grayscale chart (from the good old Q-14 color separation guide) using a photospectrometer from Kodak, which results were all below 1.0 for each Radiance RGB triplet (see the attachment, which contain the conversions of the measured xyz-values to radiance rgb ). Since then my idea has been that rgb triplet values for diffuse reflectances above 1.0 are invalid. Reading your mail I get confused a bit.
Another point I don't understand is why you suggest to use gamma correction within a material description. I always think of gamma to be applied after the simulation has been done. In other words, I think of gamma to correct an image for a certain output device. So, why should we correct reflection values with a gamma _before_ a simulation?
The idea of a public database for materials, paints etc. dedicated to Radiance would be very usefull. Imho such a database would be very valuable as a part of the Radiance distribution also. This instead of pointing to websites, which might confuse users. Measured samples from commercial color charts (like RAL, Pantone and other paints and materials) would extend the direct useability of Radiance a lot. It might be an idea to plan measurements using a photospectrometer on such standard commercial color charts, and discuss the conversion of the results within this group. Or has this already be done in such an extensive way?
-Iebele
David Smith wrote:
q14.mat (1.23 KB)
···
Mark,
That's where gamma values come in. Let's say the RGB values of a paint
sample from EasyRGB are (125,150,175), a blue gray. Take each channel,
divide by 256, take the result to the power of 2.2 (monitor gamma) and
then multiply by 256.R = (125/256)^2.2 * 256 = 52.9
G = (150/256)^2.2 * 256 = 79.0
B = (175/256)^2.2 * 256 = 110.9If you put the resulting values (52.9,79.0,110.9) in as the R G and B
material colors, you should get the correct paint color in your
simulation that matches the physical paint color.--Dave
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
I am 100% in agreement with idea of using photospectrometer validated readings of 'standard' color charts. Let me add that perhaps paint manufacturers may already have this data ready or be keen on the approach. I've been waiting for such an effort for a while and often have had to rely on Axel's color chart by default and that other construction material chart from the folks at design lab :http://www.designlaboratory.com/computing/tools/radiance/radmatlib.htmlregardssteve> Date: Fri, 7 Nov 2008 09:57:24 +0100> From: [email protected]> Subject: Re: [Radiance-general] Color reflectance values and materials..> To: [email protected]> > Hi Dave,> > As Mark already said, these values seem very bright to me also.> > Once I did some measurements on a Kodak grayscale chart (from the good > old Q-14 color separation guide) using a photospectrometer from Kodak, > which results were all below 1.0 for each Radiance RGB triplet (see the > attachment, which contain the conversions of the measured xyz-values to > radiance rgb ). Since then my idea has been that rgb triplet values for > diffuse reflectances above 1.0 are invalid. Reading your mail I get > confused a bit.> > Another point I don't understand is why you suggest to use gamma > correction within a material description. I always think of gamma to be > applied after the simulation has been done. In other words, I think of > gamma to correct an image for a certain output device. So, why should we > correct reflection values with a gamma _before_ a simulation?> > The idea of a public database for materials, paints etc. dedicated to > Radiance would be very usefull. Imho such a database would be very > valuable as a part of the Radiance distribution also. This instead of > pointing to websites, which might confuse users. Measured samples from > commercial color charts (like RAL, Pantone and other paints and > materials) would extend the direct useability of Radiance a lot. It > might be an idea to plan measurements using a photospectrometer on such > standard commercial color charts, and discuss the conversion of the > results within this group. Or has this already be done in such an > extensive way?> > -Iebele> > > > David Smith wrote:> >>Mark,>>>>That's where gamma values come in. Let's say the RGB values of a paint>>sample from EasyRGB are (125,150,175), a blue gray. Take each channel,>>divide by 256, take the result to the power of 2.2 (monitor gamma) and>>then multiply by 256.>>>>R = (125/256)^2.2 * 256 = 52.9>>G = (150/256)^2.2 * 256 = 79.0>>B = (175/256)^2.2 * 256 = 110.9>>>>If you put the resulting values (52.9,79.0,110.9) in as the R G and B>>material colors, you should get the correct paint color in your>>simulation that matches the physical paint color.>>>>--Dave>>>>_______________________________________________>>Radiance-general mailing list>>[email protected]>>http://www.radiance-online.org/mailman/listinfo/radiance-general>>>> >>>
···
_________________________________________________________________
While I agree that extending the material file in the radiance distribution would be useful for viz, I'd like to encourage those who did not try yet to use their digital cameras and a calibration tool such as macbethcal and the not too expensive chart as a measurement device. Today as almost everyone has the equipment for digital photography, this should be not too difficult. While one can certainly discuss the accuracy, obtaining an "inaccurate" sample of the material that is actually to be simulated should still be better then an accurate sample of a generic material.
That said, the most important feature of a new material database must be detailed documentation of the samples, measurement equipment, conditions.
CU Lars.
I have here a list of 50+ RAL and xKxxx (like 2K216) colors.
I don't remember where I got those from and if I'm allowed
to share them in public. I also do not know if the Radiance
RGB values are validated or 'just' calculated.
On the subject of material conversion in general I have
to confess that my own attempts to use the equations on
easyrgb.org failed and I really don't know how it should
be done. I was only concerned about the monitor RGB
to Radiance RGB bit (for Sketchup exports) but even here
I felt that a simple linear scale by 0.85 gave better results
than jumping from colour space to colour space. I finally
found a mail from Greg or Axel stating that these two RGB
spaces are so close that a big convoluted conversion is
often not necessary. And so I left it at that.
The library idea sounds appealing at first but i think the
practical value of validated colour charts is just as big as
a good conversion from the published RGB values. The
real world problem I see is that the colour changes it's
properties depending on the material it's painted on.
Take wall paint on plaster for example and compare this
with the same paint on a dense wood fibre board (HDF
or whatever you call it). The texture of the material will
change the properties of the paint.
So instead of a big honking official library a nice and
small peer-reviewed HOWTO on the conversion from
manufacturer's RGB data (and colour space) to
Radiance values would have more practical value.
I assume that there is such a conversion procedure.
If we have to measure before we get any realistic
values then a library seems to be the thing to do.
Nice job for a student in the need of a thesis ...
Yours humbly,
Thomas
···
On 7 Nov 2008, at 09:17, steve michel wrote:
I am 100% in agreement with idea of using photospectrometer validated readings of 'standard' color charts. Let me add that perhaps paint manufacturers may already have this data ready or be keen on the approach.
Hi
This RAL and xKxxx paints colors list is probably the same as the list appearing in the annex of my Radiance tutorial http://home.hefr.ch/compag/ref/RADIANCE_tutorial_E.pdf
where their reflected Yxy values (measured under the standard illuminant D65) are given.
These values were measured in years ~1991-1993 with a colorimeter at LESO-PB EPFL Lausanne (where I was working at that time) on paper paints samples. The xKxxx or xExxx color names are coming from a Swiss standard notation defined by the paints manufacturers association VSLF http://www.vslf.ch/
This tiny database was built for the ADELINE package http://www.ibp.fhg.de/wt/adeline/index.html
Raphael Compagnon
-----Message d'origine-----
···
De : [email protected] [mailto:[email protected]] De la part de Thomas Bleicher
Envoyé : vendredi, 7. novembre 2008 11:21
À : Radiance general discussion
Objet : Re: [Radiance-general] Color reflectance values and materials..
I have here a list of 50+ RAL and xKxxx (like 2K216) colors.
I don't remember where I got those from and if I'm allowed
to share them in public. I also do not know if the Radiance
RGB values are validated or 'just' calculated.
Turns out these are the materials from the materials.rad in
the standard distribution. So everybody has them already
and they seem not to be that interesting ...
Thomas
···
On 7 Nov 2008, at 10:21, Thomas Bleicher wrote:
I have here a list of 50+ RAL and xKxxx (like 2K216) colors.
I don't remember where I got those from and if I'm allowed
to share them in public. I also do not know if the Radiance
RGB values are validated or 'just' calculated.
Hi Thomas,
It would be very interesting if this list was complete. As far as I know 210 ral colors are in use for architectural applications.
-Iebele
···
On 7 Nov 2008, at 10:21, Thomas Bleicher wrote:
I have here a list of 50+ RAL and xKxxx (like 2K216) colors.
I don't remember where I got those from and if I'm allowed
to share them in public. I also do not know if the Radiance
RGB values are validated or 'just' calculated.Turns out these are the materials from the materials.rad in
the standard distribution. So everybody has them already
and they seem not to be that interesting ...Thomas
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Hi Rob,
Thanks for this, some of these look nice, but rely on non-standard .cal
files. Do you happen to have those? I can't find a link to them on
that site.
They are not linked. My impression is that some .cal files might be
from the old ConRad. I'm sending you Takayuki Otomo's e-mail address
off-list, so you can get in touch with him.
Regards
Axel
Sorry, I keep forgetting that I'm replying to the digest. Re-posted
with proper Subject line...
I have here a list of 50+ RAL and xKxxx (like 2K216) colors.
I don't remember where I got those from and if I'm allowed
to share them in public. I also do not know if the Radiance
RGB values are validated or 'just' calculated.
Jan Diepens of University of Technologie Eindhoven sent me a complete
list of RAL colours some time ago. I have to admit that they are still
not in the ColourPicker. I've put them up for your perusal:
http://luminance.londonmet.ac.uk/pickup/ral_mat.tgz
If anybody is going to translate the names to English, please bounce
the changes back to me for inclusion in the ColourPicker. The values
were measured with a Minolta chroma meter from samples. YXZ was then
converted to Radiance RGB with a Radiance .cal file, so the values
should be accurate.
Axel
Iebele,
I'm about as far removed from being a color expert as one can get. I
got the method from a thread in the forums for AGi32, and the method
has worked reasonably well for me (some tweaking required). I'm not
sure if the method is just a hack, but Ian Ashdown was the person who
suggested it, as well as some further reading on color science. Here's
the link, free registration required:
http://www.agi32.com/forums/view_topic.php?id=585&forum_id=4
Also, Konica-Minolta makes a luminance meter, CS-100A, that will give
you the XYZE values of what it's looking at, but I'm sure it costs a
small fortune. I think it's the one that Axel had just mentioned.
--Dave