LibTiff Mailing List
TIFF and LibTiff Mailing List Archive
December 2008
Previous Thread
Next Thread
Previous by Thread
Next by Thread
Previous by Date
Next by Date
Contact
The TIFF Mailing List Homepage
This list is run by Frank Warmerdam
Archive maintained by AWare Systems
Thread
2008.12.16 17:04 "Extracting layers from a TIFF file", by Richard Nolde
On Tue, 16 Dec 2008, Mitesh wrote
> > Now it is clear to me that multi pages and layers are two different beasts.
> >
> > Now I need to extract layers from a Tiff file. How should I do it? Please
> > suggest.
> Do you know how many layers are in your TIFF file? If you install
> libtiff and utilities, what is the output of 'tiffinfo' when provided
> the name of your file?
>
> My software (GraphicsMagick) may be useful but it only handles up to
> four channels ("layers"), one of which must be an alpha channel.
> There is likely other software much better at handling TIFFs with an
> arbitrary number of channels.
>
> Bob
> ======================================
> Bob Friesenhahn
The next version of tiffcrop has hooks that could be used to do this and
it is not limited to 4 channels. I posted a query to the list as to
whether this would be useful and no one replied so I only implemented it
for debugging purposes. What exactly do you mean when you say extract a
layer? Extract the raw binary data as a data dump in binary or ASCII
format or to a new TIFF file. The first case can be handled with my
debugging dump code. The later requires some information about how
various types of TIFF input files will be converted to output files. eg
RGBA to RGB may not be a big deal since you are just throwing away the
alpha channel but all current planes would have to be multiplied by the
values in the alpha channel if is is associated alpha data if I remember
correctly. However extracting one or more input channels
RGB[A][N1][N2]... to one of R,G,B,A,N1,N2 requires some interpretation
of the input data and a new definition of the output file type. Does a
single channel become a 'grayscale' image and if so, what about bit
depth conversions? If you extract any three channels from a
multi-spectral image, does it become RGB? Since I doubt that there is
any legal TIFF image type where the number of image planes is not 1,3,4
or greater than four. You probably cannot extract only two channels to a
new TIFF image.
If you can define the conversions in a way that are generally accepted
by the other members of the TIFF community, I could probably add that
support to tiffcrop in the next release after this one. The current
version in CVS will be obsoleted by the version that is soon to be
uploaded so don't bother looking at it as it has none of the code you need.
Richard Nolde
Tiffcrop author