JPEG degradation

I was reading a photography book by Bryan Peterson and he says something in
it I never knew. He said that opening JPEG's over and over........with time
they will degrade to the point to where they dont open anymore.

My question is, if on a screen saver you are doing a slide show with all the
pictures that you took, does this count as 'opening' and 'closing' of a JPEG
and will those degrade over time?

In "TSKO"
wrote:

I was reading a photography book by Bryan Peterson and he says
something in it I never knew. He said that opening JPEG's over and
over........with time they will degrade to the point to where they
dont open anymore.


That's only possible if you re-save the file after changing it somehow.

Simply opening the file to view it and then closing it without writing
to it will not change the file.

If the viewing software you're using always re-writes the file whenever
you open it for simple viewing, toss it and get something else.

--
Bert Hyman St. Paul, MN

If they are opened and not RE-SAVED, there should be no problem,
I believe.

I was reading a photography book by Bryan Peterson and he says
something in it I never knew. He said that opening JPEG's
over and over........with time they will degrade to the point
to where they dont open anymore.
My question is, if on a screen saver you are doing a slide
show with all the pictures that you took, does this count as
'opening' and 'closing' of a JPEG and will those degrade over
time?

On Thu, 25 Jan 2007 19:36:14 -0500, "TSKO" wrote:

I was reading a photography book by Bryan Peterson and he says something in
it I never knew. He said that opening JPEG's over and over........with time
they will degrade to the point to where they dont open anymore.

My question is, if on a screen saver you are doing a slide show with all the
pictures that you took, does this count as 'opening' and 'closing' of a JPEG
and will those degrade over time?

That doesn't make sense to me. Perhaps he meant that opening /and
saving/ a JPG multiple times incrementally degrades the image quality.

It seems to me that simply displaying an image should do nothing
whatsoever to the source file.

On Thu, 25 Jan 2007 19:36:14 -0500, TSKO wrote:

I was reading a photography book by Bryan Peterson and he says something in
it I never knew. He said that opening JPEG's over and over........with time
they will degrade to the point to where they dont open anymore.

My question is, if on a screen saver you are doing a slide show with all the
pictures that you took, does this count as 'opening' and 'closing' of a JPEG
and will those degrade over time?

What happens is that every time you SAVE a jpeg image it is recompressed.
There was already some degradation the last time it was SAVED or created,
so it gets worse. It does not matter in the least how many times you open
the file.

On Fri, 26 Jan 2007 00:43:26 +0000, Bert Hyman wrote:

In "TSKO"
wrote:

I was reading a photography book by Bryan Peterson and he says
something in it I never knew. He said that opening JPEG's over and
over........with time they will degrade to the point to where they
dont open anymore.


That's only possible if you re-save the file after changing it somehow.

Matters not an iota if you change it or not. Saving it will always cause
additional degredation.


Simply opening the file to view it and then closing it without writing
to it will not change the file.

If the viewing software you're using always re-writes the file whenever
you open it for simple viewing, toss it and get something else.

On Thu, 25 Jan 2007 18:27:24 -0700, ray wrote:


On Fri, 26 Jan 2007 00:43:26 +0000, Bert Hyman wrote:

In "TSKO"
wrote:

I was reading a photography book by Bryan Peterson and he says
something in it I never knew. He said that opening JPEG's over and
over........with time they will degrade to the point to where they
dont open anymore.


That's only possible if you re-save the file after changing it somehow.

Matters not an iota if you change it or not. Saving it will always cause
additional degredation.

Opening the file to view it doesn't requiring it be saved again. You should shut
the **** up about matters for which you haven't the slightest understanding.

In news wrote:

On Fri, 26 Jan 2007 00:43:26 +0000, Bert Hyman wrote:

In "TSKO"
wrote:

I was reading a photography book by Bryan Peterson and he says
something in it I never knew. He said that opening JPEG's over and
over........with time they will degrade to the point to where they
dont open anymore.


That's only possible if you re-save the file after changing it
somehow.

Matters not an iota if you change it or not. Saving it will always
cause additional degredation.

Why? If the app re-writes the same series of bytes back onto disk that
it read, there will be no change in the file or the resulting image.


--
Bert Hyman St. Paul, MN

TSKO wrote:
I was reading a photography book by Bryan Peterson and he says something in
it I never knew. He said that opening JPEG's over and over........with time
they will degrade to the point to where they dont open anymore.

This is nonsense. Opening the file doesn't change the file. This is
trivially easy to demonstrate using file-compare programs.

My question is, if on a screen saver you are doing a slide show with all the
pictures that you took, does this count as 'opening' and 'closing' of a JPEG
and will those degrade over time?

No.

The situation that's an issue is when you open, change, and *save* the
jpeg. It goes through and re-compresses it again, and because there are
changes, some of the damage this time is *different* from the damage the
first time. (I say "damage"; jpeg is a lossy compression format, that's
how it gets such small file sizes.)

Matters not an iota if you change it or not. Saving it will
always cause additional degredation.

Why? If the app re-writes the same series of bytes back onto
disk that it read, there will be no change in the file or the
resulting image.

I think in almost all cases, it does cause degredation. At least
it seems that way to me based on my own experience.

JPG is not quite like MP3 audio, which while lossless, works on
specific frequencies at a given bit depth.

Say you have an MP3 sound file and convert it to 32 kbps, 16 bit,
22 khz Mono. If you use the same program to encode, it should
use the same methodology, which would include eliminating certain
very high and very low frequencies, always according to the same
formula. When processing, no new frequencies are introduced that
can be eliminated later, I believe.

But with JPG, each time you save the file, the entire image is
altered, and each time it is edited, the entire image is
processed and saved. It's not limited to specific "colors" or a
range of pixels in specific areas, I believe, so degredation
always occurs.