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Re: what is an efficient lossless compression way to store a gray-scale image [message #36261 is a reply to message #36121]

Tue, 26 August 2003 14:24

Liam E. Gumley
Messages: 378
Registered: January 2000

Senior Member

"Xiaoying Jin" <xje4e@mizzou.edu> wrote in message
news:10ea38a6.0308260652.6a1e1b9a@posting.google.com...
> Hi, there,
>
> For a gray-scale image, I haven't found a good way to store it yet. It
> seems that there is no way to store gray-scale images in IDL
> efficiently. If so, that will be too bad, because all the satellite
> images we processed are very large and occupy a lot of space.
>
> I tried 'tiff' format with Packbits compression, but it does not help
> for gray-scale image. Sometimes the file size of the compressed image
> is even larger than the original raw data!!!
>
> Can anyone give me some hint? Thank you very much!

If you use the OPEN routine to open the files for reading and writing, then
use the COMPRESS keyword to activate GZIP compression:

"If COMPRESS is set, IDL reads and writes all data to the file in the
standard GZIP format. IDL's GZIP support is based on the freely available
ZLIB library version 1.1.3 by Mark Adler and Jean-loup Gailly. This means
that IDL's compressed files are 100% compatible with the widely available
gzip and gunzip programs. COMPRESS cannot be used with the APPEND keyword."

This method will automatically compress/decompress any data type you wish to
read or write in IDL.

Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com/

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[Message index]

		what is an efficient lossless compression way to store a gray-scale image By: xje4e on Tue, 26 August 2003 07:52
		Re: what is an efficient lossless compression way to store a gray-scale image By: George N. White III on Wed, 27 August 2003 15:52
		Re: what is an efficient lossless compression way to store a gray-scale image By: Liam E. Gumley on Tue, 26 August 2003 14:24
		Re: what is an efficient lossless compression way to store a gray-scale image By: R.G. Stockwell on Tue, 26 August 2003 10:55
		Re: what is an efficient lossless compression way to store a gray-scale image By: xje4e on Tue, 26 August 2003 10:23
		Re: what is an efficient lossless compression way to store a gray-scale image By: Jonathan Boswell on Tue, 26 August 2003 10:23
		Re: what is an efficient lossless compression way to store a gray-scale image By: R.G. Stockwell on Tue, 26 August 2003 09:42

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