Started Feb 17, 2008 | Discussions thread
Ray Ritchie Veteran Member • Posts: 4,012
Re: All generalizations are wrong...

SecondWindShooter wrote:

You are missing the point of (or simply ignoring) what I said.

No matter how many ad-hoc putative "test" images one might care to
post, they will all be subject to too many other variables (not least
being the need to convert them to JPEG for posting in the first
place) to make such "comparisons" meaningful.

More to the point, and particularly telling... You have not answered
my challenge.

I have not answered your challenge because I consider it rather meaningless - you asked someone to show how discarding information can be a "good" thing for image quality. It is obvious that the whole purpose of discarding information has nothing to do with improving image quality. Rather, the purpose is to preserve quality as well as possible while greatly reducing the number of bytes that need to be stored. We all know this. The important question is "how much damage is done?" by discarding the information.

You have repeatedly tried to imply, by citing your statistic that "93-98% of the original information is being thrown away," that JPEG's are necessarily grossly inferior. I'm not claiming they are "as good as" raw, but I do claim the differences between the two are becoming quite small, given the state of today's technology.

A statistician friend of mine used to have a sign in his office that said "In God we trust - all others, please bring data." You have not brought any new data to this discussion.

"Better" is the enemy of "good enough". But even the fact that you
put the argument in those terms tends to make my case.

As I have said before, JPEG really is a marvel of clever coding, and
a wonderful format for what it was originally intended for --
primarily the WWW, where the compactness of (sanely created) JPEG
files makes it feasible to transfer images over relatively slow links
like dial-up lines). In a sense, it's almost too good; for the
very fact that it is so often perceived as "good enough" leads to
folks MISapplying it to things it is just not well-suited for -- such
as the "definitive" storage of digital camera images.

Actually, JPEG was developed in ISO and the CCITT before the inception of the WWW. The technical papers discussing the creation of the standard are full of references to photographic applications, including desktop publishing, graphic arts and medical imaging (the last being arguably the world's most demanding imaging application, as failure to preserve detail can be a true matter of life and death).

As to the issue of using JPEG for "definitive" storage of image data, here's a link to a discussion on that point which is currently going on among archivists:


Those particular experts are not yet agreed, but there seem to be many who feel JPEG is indeed "good enough" for that demanding application.

All life is a matter of making decisions about "good enough." I make daily decisions of "good enough" in all details of my personal life, such as what car or house or camera to buy, and how often to maintain them. In photography, I shoot a lot of NEF's, especially when I know I may want to do large prints of the images - but JPEG's are frequently "good enough," and choosing to shoot them, or to save the JPEG and throw the NEF away, is not necesarily "dumb."

Ray Ritchie

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