[OSGeo-Discuss] 'lossless' JPEG2000

[Michael P. Gerlek]

JPEG 2000 is a method for encoding raster images, in such a way that in
the encoded version the image has special properties -- ability to
extact "down-sampled" versions (with data loss), ~2x space savings, etc
-- while still retaining all of the original data.  You can read the ISO
spec and verify the math, if you wish, to prove the encodings are
lossless, or alternatively you can trust the experts on the ISO
committee.
 
One can optionally choose to throw away bits while doing the encoding
(or after), but that is outside the realm of the JP2 encoding spec per
se.  Modulo metadata, you can't tell if the image has undergone lossy
compression or not.
 
Again, what format do you store your data in now, and what "proof" do
you use to show it is lossless?  (Just to be sure: you do know that the
data that you receive from your satellite ground station is not
bit-for-bit identical with the data that comes off the sensor unit on
the satellite?)
 
If you'd like to get me samples of your data, either by FTP or CD, I'd
be happy to encode them into JP2 format and point to some decoders you
can use yourself to verify the data is indeed lossless (modulo
metadata).  Futhermore, here at LizardTech, we run regression tests on
hundreds of images of all different data types on multiple HW and SW
platforms on a 24x7 basis, and we'd be happy to include your data in our
regression suite.
 
-mpg
 

 

________________________________

	From: discuss-bounces at lists.osgeo.org
[mailto:discuss-bounces at lists.osgeo.org] On Behalf Of
Bruce.Bannerman at dpi.vic.gov.au
	Sent: Monday, February 25, 2008 7:39 PM
	To: OSGeo Discussions
	Subject: RE: [OSGeo-Discuss] 'lossless' JPEG2000
	
	

	IMO: 
	
	
	Michael, 
	
	Thanks for the comments on this thread. 
	
	I've had a couple of private emails expressing interest in the
outcome, so I'll continue this conversation in public, rather than
moving it offline. 
	
	
	One of the problems that I have is that I understand that JPEG
2000 can be 'lossy' or 'non-lossy'. 
	
	(Is there a way to tell if a JPEG2000 file is lossy or not?) 
	
	
	I don't pretend to understand the maths behind wavelet
compressions. 
	
	I have also not seen 'proof' that would convince me I would be
able to  safely compress all of my imagery using JPEG2000, (potentially)
throw away my source imagery and feel confident that I'd be able to run
image processing routines on the radiometric 'numbers' of the imagery at
some undefined point in the future with confidence in the integrity of
the results. 
	
	As a reminder, when talking about 'imagery', I'm using the term
in its broadest sense to include data such as multi and hyperspectral
data in the umbrella term 'imagery'. I'm not talking about only three
bands displayed as Red, Green and Blue, but **all** the bands in the
'file'. 
	
	
	The description of a test that I included in the early stages of
this thread would give me a degree of confidence that JPEG 2000 was a
suitable format for long term archival of image data. 
	
	All that I'm seeing at the moment from many people and
organisations is something to the effect of "Trust me, your data is
saved using a loss-less compression." 
	
	
	Bruce 
	
	
	
	
	discuss-bounces at lists.osgeo.org wrote on 26/02/2008 04:27:22 AM:
	
	> Bruce- 
	>   
	> Again, I'm not sure how to convince you of this...  JP2 is 
	> inherently lossless just like GeoTIFF is; what arguments do
you / 
	> would you find persuaive to use GeoTIFF?  (alternatively, what
do 
	> you use now that you trust?) 
	>   
	> [feel free to take this to private email, this is probably a
bit 
	> esoteric for the rest of the OSGeo crowd] 
	>   
	> -mpg 
	>   
	> 
	
	
	
	

	Notice:
	This email and any attachments may contain information that is
personal, confidential,
	legally privileged and/or copyright. No part of it should be
reproduced, adapted or communicated without the prior written consent of
the copyright owner. 

	It is the responsibility of the recipient to check for and
remove viruses.

	If you have received this email in error, please notify the
sender by return email, delete it from your system and destroy any
copies. You are not authorised to use, communicate or rely on the
information contained in this email.

	Please consider the environment before printing this email.

	 

	 

	 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/discuss/attachments/20080226/7e615648/attachment-0002.html>