Colorpict question

Hi,

I want to define a material with colorpict pattern, and I plan to use non calibrated digital photos of a material sample taken by ordinary camera.
If I know the average reflectance of the real material (r ,g ,b) is the material defined with next procedure physically correct:
1)normalize photos average brightness with normpat
2)use it in a colorpict primitive:
void colorpict pattern1
7 red green blue picture_norm.pic picture.cal tile_u tile_v

1 A1

3)define basic material with the average grey reflectance as a real material:
void plastic mat1

5 grey(r,g,b) grey(r,g,b) grey(r,g,b) 0 0

4) define alias:
pattern1 alias mat_with_pat material1

I've read previous posts on similar topics, but most of the images mentioned were already calibrated, so I'm not sure if resulting material in my example would have appropriate appearance (pattern) and still appropriate reflectance (basic material). Of course I don't expect to obtainr 100% accurate reflectance in each point of the material :slight_smile:

Thanks,
Marija

Marija.

The idea is to define a pattern in step 2 and use this
pattern as a base for the material definition in step 3:

void colorpict pattern1
7 red green blue picture_norm.pic picture.cal tile_u tile_v
0
0

pattern1 plastic material1
0
0
5 0.4 0.4 0.4 0 0

This will create 'material1' with an average reflectance
of 0.4. You can use 'material1' directly in your scene, there
is no need to define an alias.

Using a normalised picture allows you to change the material
reflectance by changing the rgb-arguments in the plastic
primitive (here: 0.4) directly. You don't have to take into
account the average of the picture as well because the average
of the normalised image is 1.

You don't have to use a digital image as source (normpat will
take care of that, too). Only if you want to use the image
as illumination source you need a properly calibrated HDR image
which can only be obtained with a digital camera.

I have a few comments on image maps here:

http://home.arcor.de/tbleicher/radiance/imagemaps.html

HTH,
Thomas

···

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On
Behalf Of [email protected]
Sent: 26 March 2007 08:18
To: [email protected]
Subject: [Radiance-general] Colorpict question

Hi,

I want to define a material with colorpict pattern, and I
plan to use non calibrated digital photos of a material
sample taken by ordinary camera.
If I know the average reflectance of the real material (r ,g
,b) is the material defined with next procedure physically correct:
1)normalize photos average brightness with normpat 2)use it
in a colorpict primitive:
void colorpict pattern1
7 red green blue picture_norm.pic picture.cal tile_u tile_v

1 A1

3)define basic material with the average grey reflectance as
a real material:
void plastic mat1

5 grey(r,g,b) grey(r,g,b) grey(r,g,b) 0 0

4) define alias:
pattern1 alias mat_with_pat material1

I've read previous posts on similar topics, but most of the
images mentioned were already calibrated, so I'm not sure if
resulting material in my example would have appropriate
appearance (pattern) and still appropriate reflectance (basic
material). Of course I don't expect to obtainr 100% accurate
reflectance in each point of the material :slight_smile:

Thanks,
Marija

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Thanks Tomas,

You don't have to use a digital image as source (normpat will
take care of that, too). Only if you want to use the image
as illumination source you need a properly calibrated HDR image
which can only be obtained with a digital camera.

No, I need image as a simple pattern on the floor. If I understood you well I can use any image, as long as I know the average reflectance of the material.

I have a few comments on image maps here:

http://home.arcor.de/tbleicher/radiance/imagemaps.html

Nice page, but I think that picture aspect can be set with A1 variable in colorpict definition :slight_smile:

void colorpict pattern1
7 red green blue picture_norm.pic picture.cal tile_u tile_v

1 A1

Thanks again,
Marija

[email protected]:

No, I need image as a simple pattern on the floor. If I
understood you well I can use any image, as long as I know
the average reflectance of the material.

Right. Think of the total reflectance as material reflectance
multiplied by 'colour reflectance'. If your image has an average
reflectance of 1 (after normpat) the result is equal to the
material reflectance.

> I have a few comments on image maps here:
>
> http://home.arcor.de/tbleicher/radiance/imagemaps.html
>
Nice page, but I think that picture aspect can be set with A1
variable in colorpict definition :slight_smile:

void colorpict pattern1
7 red green blue picture_norm.pic picture.cal tile_u tile_v

1 A1

Right. There are a few things I should add to that page.

Regards,
Thomas

···

***********************************************************************************
This e-mail, (and any attachments) is confidential and may be privileged. It may be read, copied and used by the intended addressee only. If you have received this in error please contact BDP immediately.

If you have any queries, please contact the sender.
***********************************************************************************
Building Design Partnership
Registered in England No 2207415:
Registered Office: Building Design Partnership Ltd, Sunlight House, PO Box 85, Quay Street, Manchester, M60 3JA, http://www.bdp.co.uk
***********************************************************************************