LibTiff Mailing List

On Wed, 11 Jan 2006, NGUYEN QUANG BANG wrote:
>  
> I have a problem while reading a 16 bits grayscale TIFF image.
> when i use the function TIFFReadRGBAImage and TiffReadEncodedStrip, they
> give different results.
> When i read this image using MatLab, it gives the image with the pixels have
> value RGB as result of TIFFReadRGBAImage,and the corresponding index as the
> result of TiffReadEncodedStrip function.

TIFFReadRGBAImage() is a higher level function than 
TiffReadEncodedStrip().  The TiffReadEncodedStrip() function returns 
the raw-uncompressed data from the TIFF.  This data could be indexes 
into a colormap containing 16-bit RGB color samples.  Or it could be 
raw gray samples.  But TIFFReadRGBAImage() always represents the image 
as TrueColor RGB so it must used the indexes and the colormap (or the 
raw gray samples) to create the equivalent (or as close as possible) 
TrueColor RGB image.  For your gray image, TIFFReadRGBAImage() needs 
to emulate the gray by using equal parts of red, green, and blue.

TIFFReadRGBAImage() is intended for casual libtiff users that don't 
have the time to deal with the many permutations of the TIFF format.

So what is your question?

Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/


AWARE [SYSTEMS]		Imaging expertise for the Delphi developer
		TIFF and LibTiff Mailing List Archive
	LibTiff Mailing List TIFF and LibTiff Mailing List Archive January 2006 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 2006.01.11 02:01 "help on reading a 16bits grayscle TIFF image", by Nguyen Quang Bang 2006.01.11 02:40 "Re: help on reading a 16bits grayscle TIFF image", by Bob Friesenhahn 2006.01.11 02:40 "Re: help on reading a 16bits grayscle TIFF image", by Bob Friesenhahn On Wed, 11 Jan 2006, NGUYEN QUANG BANG wrote: > > I have a problem while reading a 16 bits grayscale TIFF image. > when i use the function TIFFReadRGBAImage and TiffReadEncodedStrip, they > give different results. > When i read this image using MatLab, it gives the image with the pixels have > value RGB as result of TIFFReadRGBAImage,and the corresponding index as the > result of TiffReadEncodedStrip function. TIFFReadRGBAImage() is a higher level function than TiffReadEncodedStrip(). The TiffReadEncodedStrip() function returns the raw-uncompressed data from the TIFF. This data could be indexes into a colormap containing 16-bit RGB color samples. Or it could be raw gray samples. But TIFFReadRGBAImage() always represents the image as TrueColor RGB so it must used the indexes and the colormap (or the raw gray samples) to create the equivalent (or as close as possible) TrueColor RGB image. For your gray image, TIFFReadRGBAImage() needs to emulate the gray by using equal parts of red, green, and blue. TIFFReadRGBAImage() is intended for casual libtiff users that don't have the time to deal with the many permutations of the TIFF format. So what is your question? Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/

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2006.01.11 02:40 "Re: help on reading a 16bits grayscle TIFF image", by Bob Friesenhahn