tag:blogger.com,1999:blog-3808045742964712463.post5783670768881163773..comments2022-10-31T11:16:55.967+00:00Comments on JPEG 2000 at the Wellcome Library: Lossy v. lossless compression in JPEG 2000Christy Henshawhttp://www.blogger.com/profile/13179015500410216822noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-3808045742964712463.post-79955905817604588992011-02-07T09:05:06.380+00:002011-02-07T09:05:06.380+00:00Hi Ron,
Thanks for your comment. We are talking a...Hi Ron,<br /><br />Thanks for your comment. We are talking about JPEG 2000 specifically here (which is a completely different format to JPEG, although the name is confusing!). Do you mean to ask about JPEG 2000, or JPEG?<br /><br />Regarding how much compression is lossy and how much is lossless - with JPEG 2000 (.jp2/.jpf) you can choose to compress lossless (a more effecient way to store data, but all the data is retained), and lossy, where data is actually discarded. Much of the discarded data is noise. I'm not sure about the JPEG format though (.jpg) - I don't think there is a lossless option.Christy Henshawhttps://www.blogger.com/profile/13179015500410216822noreply@blogger.comtag:blogger.com,1999:blog-3808045742964712463.post-34579073475095972222011-02-06T18:00:31.206+00:002011-02-06T18:00:31.206+00:00Thank you for this explanation. I've been a ph...Thank you for this explanation. I've been a photographer for 50 years and digital now for almost twenty. I switch off from jpg to raw based on my output needs (once I got into the 15 megapixel range) the loss is simply not worth discussing in many of my shots without a microscope which is the only way to discover that there WAS loss!<br /><br />I do have one question for you though. In an "average" jpg file compression how much of that compression is lossy and how much lossless? I know it depends on redundant information.. I'm just trying to get a handle on a RAW file reduced to 10% of its original size in a jpg. It can't all be loss.<br /><br />Ron SmithRonhttps://www.blogger.com/profile/06431824622684783442noreply@blogger.comtag:blogger.com,1999:blog-3808045742964712463.post-41298066232691818092010-07-21T09:12:41.251+01:002010-07-21T09:12:41.251+01:00Bedrich - please see post dated July 21, 2010, whi...Bedrich - please see post dated July 21, 2010, which addresses these issues in more detail. Cheers, ChristyChristy Henshawhttps://www.blogger.com/profile/13179015500410216822noreply@blogger.comtag:blogger.com,1999:blog-3808045742964712463.post-57459206446650086482010-07-19T10:50:20.354+01:002010-07-19T10:50:20.354+01:00Hi Bedrich,
Thanks for your comment - you raise a...Hi Bedrich,<br /><br />Thanks for your comment - you raise a very interesting point, and something we have factored into our thinking. We are in fact about to post on this very topic, hopefully this week.<br /><br />I guess my immediate reaction to this is, while yes migration will introduce new algorithms, this should be managed in such a way that visual lossless-ness is maintained. It would also be my hope that, considering the long timescales when we think about many migrations, conversion algorithms and format design will become ever better at recreating and retaining information in an efficient way. However, I will defer this discussion to my colleague, a Digital Curator, and his upcoming blog post...Christy Henshawhttps://www.blogger.com/profile/13179015500410216822noreply@blogger.comtag:blogger.com,1999:blog-3808045742964712463.post-52800593538053910302010-07-19T05:05:18.317+01:002010-07-19T05:05:18.317+01:00Hello Christy Henshaw,
I mostly agree with your ar...Hello Christy Henshaw,<br />I mostly agree with your article. However migration as significant part of long-term preservation was not mentioned. In my opinion this is one of the biggest threats. My concern is; when we use lossy compression for our MC (Master Copies) in large scale what will happen with our data during future migrations? We will need to migrate, because each format becomes soon or later obsolete.<br />There is just an example of simple migration. <br />Let’s start with TIFF format /1:1 no compression/ as our MC. Due to space capability was TIFF migrated to JPEG /1:10 DCT (Discrete cosine transform) irreversible/ and the original TIFF-MC was deleted. Now we have only JPEG-MC for which we used visually lossless compression. The next step will be migration into JP2-MC /1:10 DWT (Discrete wavelet transform) irreversible/ again visually lossless compression. And the next step would be migration JP2 into “Let It Wave” /DFWW (Discrete Frequency Warped Wavelets)/ again visually lossless compression and so on.<br />How we can see we use, different algorithms for each migration. Each algorithm creates significantly different artifacts. I could be OK for few migrations, because we used very “light” compress ratio (visually lossless). I am highly concern that those artifacts will grow through each migration and become more and more pronounced in the future. There are other threats such as color shifts during migration process etc.<br />As a rather expensive process we do not want to rescan our data after set of unsuccessful migrations. In my opinion it would be better to use mathematically lossless compression for Master Copies. Each representation of data could be decompressed as it was before migration.<br />I would like to ask you if you know about any research which is focusing on such the issue.Bedrichhttps://www.blogger.com/profile/17532328267814513467noreply@blogger.com