re[2]: [cgmo-webcgm] draft text- CGM gzip compression

[Don <dlarson@cgmlarson.com> (By way of dlarson@cgmlarson.com)]

Rob,

>  Don,

>  Just to be clear, it is only the binary encoded form of CGM that can be
>  compressed to CGZ format, right?

Technically, it could either binary or clear text; but that should be clarified.

>  I am curious as to how much compression can be achieved with different types >  of CGMs; i.e. vector elements only, raster elements only, mixed, etc.  Have
>  you (or anyone else in the group) done any investigations on this?

I have run some tests and found that I could get 35 to 85 percent
compression.

These CGMs were a mixture of vector and raster CGMs from both oil-field
type and technical illustrations. I got the best compression on some very
large oil-field cgm files that were comprised 80-90% vector data.

I've attached the spreadsheet with the results of my testing fyi.

Don.

>  Rob

>  -----Original Message-----
>  From: Don Larson [mailto:dlarson@cgmlarson.com]
>  Sent: Wednesday, March 05, 2008 1:24 PM
>  To: CGM Open WebCGM TC
>  Subject: [cgmo-webcgm] draft text- CGM gzip compression


>  All

>  Insert under 1.2 Normative references:

>     RFC 1952
>       GZIP file format specification

>  Insert new section under 2.4 Encoding:

>  2.4.1 Compression

>  HTTP/1.1 allows for compressed data to be passed from server 
>  to client,
>  which can result in significant file size reduction.  CGM 
>  data maybe 
>  compressed for transmission using gzip compression. It is 
>  recommended 
>  that gzip-compressed CGM files have the extension ".cgz" (all 
>  lowercase)
>  on all platforms.

>  (gzip should be linked to)  
>  http://www.ietf.org/rfc/rfc1952.txt

>  Questions- 

>  Do we need to add CGZ under MIME type section of W3C Overview 
>  of WebCGM Profile?
>  http://www.w3.org/Graphics/WebCGM/

>  Normative reference to? http://www.iana.org/assignments/media-
>  types/image/cgm

>  Regards,
>  Don

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cgm-gzip-analysis.xls