Talk:JPEG

From Academic Kids

There was a computer virus alert earlier this year regarding the JPEG format. Evidently, there's some way to hide a virus in a jpeg file, and have the virus activate when the jpeg is loaded in a typical viewer. This would be good info to include, but I would want to research and verify the details first. Perhaps someone will beat me to it? Wesley

There is some weird virus that attaches itself to JPEG files. (Un)fortunately, JPEG files cannot be executed on any computer I know of, so the virus will never be activated. The writer might as well have written a computer virus that attaches itself to lamp shades, that would have the same effect. See [1] (http://www.theregister.co.uk/content/archive/25718.html).--branko

Unless there's a buffer overrun or similar exploit for some commonly-used JPEG decoder library... -- The Anome 09:22, 1 Sep 2004 (UTC)

iirc there was (iirc it was in a microsoft implementation) Plugwash 20:48, 2 Apr 2005 (UTC)

Contents

1 graphics 2 external link 3 typo to be fixed 4 The matrix reformatted?

graphics

pl:JPEG If you would like to use some graphic for this topic.

There's an online Polish-English translator (http://www.poltran.com/) that does one sentence at a time, though results can be sketchy. (unsigned comment by Ke4roh

anything that uses the % sign when describing jpeg quality has no credibility whatsoever sorry Plugwash 20:48, 2 Apr 2005 (UTC)

external link

Are you sure the "Compress JPG and GIF images" link is appropriate for this article? The site looks quite commercial, but I didn't delete it since I didn't know if someone put it there on purpose or if was simply vandalism. TheListener

mmm link didn't work at all for me i'll try it again later. Plugwash 20:48, 2 Apr 2005 (UTC)

typo to be fixed

In the example 8 by 8 matrix to be put through the jpeg compression algorithm, there is something wrong with the entry 68 in row 6, column 6, because subtracting 128 does not give the asserted result -65 in the next displayed matrix. It is not clear which of the two matrices is wrong, except that the discrete cosine transform result matches the second matrix rather than the first. These matrices, with same inconsistency, also appear in the second edition of the Gonzalez/Woods book Digital Image Processing, second editon, page 499. Hopefully the author of this page can clear up the inconsistency. ---- 24.118.95.84 (sig added by Cburnett)

How's that now? Cburnett 03:58, Apr 19, 2005 (UTC)

Not sure. Which of the two numbers was wrong? ---- 24.118.95.84 (sig added by Cburnett)

You'll have to go into the history and check. I re-ran all the numbers and just pasted them in. Cburnett 02:11, Apr 20, 2005 (UTC)

I contacted the original author of the example to determine which of the numbers to correct. The correct fix is to 63. ---- 24.118.95.84 (sig added by Cburnett)

You're point is irrelevant as everything is based on the matrix here. Changing them requires changing of *ALL* the numbers. There are enough discrepancies in Gonzalez & Woods numbers that I didn't copy the numbers but generated them on my own.

So stop reverting as you're invalidating all the numbers. Cburnett 22:47, Apr 22, 2005 (UTC)

OK. Fine. That's what I wanted to know - that you had recalculated them all. I was in the process of writing code to do it myself, for the same reason you gave, but I am happy to have it done by you.

The matrix reformatted?

The numerical matrices are in what looks to me like a *terribly* old-fashioned font (probably through association with similar fonts I've seen in antiquated schoolbooks). They're also so wide that when viewed at 800 pixels width (which I often do when using a Favorites or History sidebar in IE6) the right hand side of some tables disappears behind the images on the right. Lee M 00:39, 3 May 2005 (UTC)

A lot of web viewers sitll use 800x600; it's about 30% of the browsing public. Time to fix it. Samboy 09:02, 3 May 2005 (UTC)

yeah its mediawiki math markup being rendered as png

maybe there is some other way to do the matrixes that will work better (is there any particular reason for them to look like maths matrixes rather than more generic grids of numbers?) Plugwash 10:14, 3 May 2005 (UTC)

As the author of the data, you're going to have to explain to me the difference between a matrix and a "grid of numbers".

Regarding the "*terribley* old-fashioned font", do you never read any math articles? Like covariance matrix or List of integrals of rational functions. It's TeX. Cburnett 14:21, May 3, 2005 (UTC)

I think we should use a different font than the one TeX uses; it doesn't look that great against the sans-serif font what we use for articles. Samboy 04:41, 16 May 2005 (UTC)

This is the incorrect place for such a discussion... Cburnett 23:11, May 22, 2005 (UTC)

Imo the issue at hand here is if its appropriate to use matrix math markup for a table of numbers that afaict has basically nothing to do with matrix algebra etc. Plugwash 12:22, 23 May 2005 (UTC)

A matrix IS a table of numbers. MATLAB stores images as matrices and there's really no difference between a 2-D array and a matrix. Simply because the subimages in question are not used as linear algebra matrices will not compel me to agree to switch to another form of representation of the same numbers. Cburnett 16:16, May 25, 2005 (UTC)