ECW performance and licensing questions

karsten karsten at
Tue Aug 11 14:47:20 EDT 2020

Hi Mark

really good question. Some ten years ago I looked into rendering speed
/versus data storage requirements (with huge imagery data collections on the
fly ) involving multiple  rendering engines and different formats and ran
some tests. 
While I am not directly answering your initial question but I would
recommend to step back for a moment and consider one more time what you
really would like to accomplish - before moving forward and getting into
possible nitty gritty licensing issues and so on.

Here are some of the things to consider:

How many images are you about to serve (total data volume , number of images
and respective storage space needed) and if it would be an issue (cost wise
) if you would instead store that image collection in an uncompressed
format. Or ... if altogether you would want to pre-render map tiles for web
serving from those images with tile engines like MapCache or MapProxy or the
like ....

In general there is a tradeoff between file format, overall storage (file)
size and rendering speed: 
If imagery is compressed (such as in MrSid or also ECW) does matter because
MapServer (and other rendering engines) rendering times' depend on that.
Traditionally compressed imagery can be slower to render (because it has to
be decompressed before being served). That also depends on the software
used. In general MapServer is a very fast engine but compressed imagery can
slow it down vs. non compressed formats.
I did get very good resets with especially prepared tiff files : with added
overviews (e.g. with gdaladdo) and that are internally tiled and jpeg
compressed. That is a really good option to consider - see Paul Ramsey's old
post on how to get it done right :

Another nice image rendering software that works well with jpeg2000 data in
IIP Images server, I am not sure about the current licensing issues with the
kakadu library used though - check it out
here and example here



Date: Mon, 10 Aug 2020 20:50:25 +0000
From: Mark Volz <MarkVolz at>
To: "Discussions for MS4W (MapServer for Windows)"
	<ms4w-users at>
Subject: [MS4W-Users] ECW performance and licensing questions
Message-ID: <8d845ea042fa4d989c9f1b822a193b4d at>
Content-Type: text/plain; charset="us-ascii"


I am trying to figure out if it might be worthwhile to consider using ECW
files instead of MrSid files.  I am wondering if ECW performs better than
MrSID.  In addition, I am curious if there is any licensing restrictions.
When I look at the documentation implies that we need a license to
use ECW on a server.  However in the MS4W documentation we can enable ECW by moving a file
around.  Perhaps the version packed with MS4W is old enough that there are
no license concerns?

Thank You!

Mark Volz

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