Ken,
If you apply the formula:
samples * lines * 3 channels (RGB)
you will know the total size of the file.
Tiff and Geotiff can use color indexed and the LZW compression that is very
good, but is patented. Ermapper only works with color in RGB model.
An interesting format for images of maps is PNG (Portable Network Graphic or
"PING") you can use this format with interenlaced for publishing maps in the
web. The output is better that ecw images for data in 256 colors (indexed).
Regards,
////
(@ @)
(_)
_______________o00o_______o00o_________________
Ge�g. Gabriel Origel-Guti�rrez
E-mail [EMAIL PROTECTED]
>From: "Leo Romeyn" <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: "ER Mapper Discussions" <[EMAIL PROTECTED]>
>Subject: Re: why ERMapper file large?
>Date: Tue, 11 Sep 2001 18:14:38 -0500
>
>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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