FW: Colour STL file format

From: Bibb, Richard (PDR) (RBibb-pdr@uwic.ac.uk)
Date: Fri Jun 13 2003 - 10:18:56 EEST

As requested by Holmer,

Please find below the replies about colour STL files.


Dr. Richard Bibb
Head of Medical Applications
Western Avenue

Tel. +44 (0) 29 2041 6723
Fax. +44 (0) 29 2041 6973


Dear Richard,

You're right, each facet has an RGB-code. We have 2 bytes, so 5 bits a color
+ 1 bit indicating if the traingle color is applied or not.

Please find the complete description of the STL-color format used by
Materialise at following link:



Pieter Bourgaux

Application engineer

Tel +32 16 39 66 66
Fax +32 16 39 66 00

No time to fix a file ? STLfix.com does it for you !
On-line around the clock STL repair and CAD to STL conversion.
"No cure, money back" guarantee. http://www.stlfix.com

Dear Richard,

attached you will find an extension for the STL format to use colour
information which has been published to the rp-ml some time ago from
Mr. Aad van der Gest (http://home.planet.nl/~spitstec/).

Within the STL binary format each triangle is defined by a section of
The first 48Byte are used to describe the geometry information of the
triangle (triangle normal and points). The remaining 2Byte in the attribute
count are reserved for further information, but the interpretation of this
information is undefined within the "original" STL specification (should be
set to zero as default).

For every triangle the colour information is described
in the attribute count (16 bits).
bit 15 always 1 (to distinguish from normal stl files)
bit 10 to 14 intensity level for red (0 to 31)
bit 5 to 9 intensity level for green (0 to 31)
bit 0 to 4 intensity level for blue (0 to 31)
In this way there are 32768 different colours.

Attached you will find a colored STL file for testing the STL color
It contains a simple cube with colored faces (red, green, blue, yellow,
and white). Further colour examples can be downloaded from our website at

We are using this extension within our VisCAM RP software and we know that
others like TNO are using the colour extension in the same way within their
STL Painter software.

But there is no "official" standard for colour within the STL format and
Materialise for example is using an extension with a different bit order
within their Magics RP software.

Therefore, colored STL files are not always comparable to each other.

Best regards
Marcus Joppe

Marcus Joppe Marcam Engineering GmbH
Managing Director Fahrenheitstraße 1
                           D-28359 Bremen
                           Tel.: +49 (0)421/2208-336
eMail: mjoppe@marcam.de Fax: +49 (0)421/2208-337

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