Hi Ken:
The file size difference is due to the type of Image e.g.: Index Color
versus RGB. ER Mapper uses RGB for Color Images. Therefore if you use a 1
channel Index Color Image and bring the Image into ER Mapper, the Image will
be transferred to a 3 channel RGB Image. You can try this out in Photoshop
under Image/Mode and you will notice the difference in file size.
Best regards,
Leo J. Romeyn
Satellite Imaging Corporation/
Geodetic Positioning Service, Inc.
12777 Jones Road, Suite 370
Houston, TX 77070
Tel: 832.237.2900
Fax: 832.237.2910
E-mail: [EMAIL PROTECTED]
Web: www.satimagingcorp.com
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Kenneth Hickey
Sent: Saturday, September 08, 2001 8:50 PM
To: [EMAIL PROTECTED]
Subject: why ERMapper file large?
G'day all
I was wondering if someone could explain to me why ERMapper files are so
large. I opened a 4Mb USGS DRG GeoTiff in ERMapper and to re-save it as an
8-bit ERMapper Raster file (.ers) or an uncompressed Geotiff it is 97Mb in
size. If I use LZW compression on the Geotiff it comes down to 12Mb
(Interestingly, if I open the same 4Mb GeoTiff in Photoshop and re-save
it, it comes out at 32MB uncompressed and 17Mb LZW compressed).
Why is the ERMapper raster format so large and is there a lossless
compression option to reduce file sizes? Why is ERMappers uncompressed
Geotiff so large?
Cheers
Ken
------------------------------------------------------------------
Dr Kenneth Hickey
Mineral Deposit Research Unit (MDRU)
Department of Earth and Ocean Sciences
University of British Columbia
6339 Stores Rd, Vancouver, BC V6T 1Z4, Canada
phone +1-604-822-3765; Fax +1-604-822-6088
email: [EMAIL PROTECTED]
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