coping files & file reduction

  • Thread starter Thread starter Zack
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Zack

is it true that when you copy a file it starts to reduce it's quality?
if so how do you prevent it from happening? does the same thing happen
when you burn your photos or data to cds/dvds?
 
Not true, computers do a digital copy with CRC cyclic reduncy check to get an
exact copy.
While it is true that making copies of analog tapes will reduce the quality,
this doesn't apply with digital files in a compuer

"Zack" wrote:

> is it true that when you copy a file it starts to reduce it's quality?
> if so how do you prevent it from happening? does the same thing happen
> when you burn your photos or data to cds/dvds?
>
 
"Zack" <xxx> wrote in message
news:K9OdnV89zMkcE-zanZ2dnUVZ_g6dnZ2d@comcast.com...
> is it true that when you copy a file it starts to reduce it's quality?

No, it is not true. Digital copies are not the same as analog, where
there can be loss and added noise due to the nature of the media and the
transfer process.

However, if the copy is also *compressed*, which will happen, for example,
with WAV to MP3 conversion, there will be a loss in dynamic range, and that
can certainly be considered a reduction in quality.

If all the settings are the same, though, either the copy is identical to
the original or it is corrupt and will likely fail the CRC (cyclic
redundancy check) testing that most if not all utilities use to ensure that
the copying process worked properly.

> if so how do you prevent it from happening?

Don't use compression when you copy (if the source file is already
compressed, this really doesn't matter).

> does the same thing happen
> when you burn your photos or data to cds/dvds?

With photos, only if you use compression or reduce the image size and
complexity.

Changes to data is, strictly speaking, corruption.

HTH
-pk
 
On Tue, 25 Dec 2007 17:13:01 -0600, Zack <xxx> wrote:

> is it true that when you copy a file it starts to reduce it's quality?


No. That's true of analog copies (for example, audio tapes ) but not
at all true of digital ones. A digital copy either fails entirely, or
is identical to the original.

--
Ken Blake, Microsoft MVP Windows - Shell/User
Please Reply to the Newsgroup
 
Re: copying files & file reduction

Zack wrote:
> Is it true that when you copy a file it starts to reduce its quality?
> If so, how do you prevent it from happening? Does the same thing happen
> when you burn your photos or data to cds/dvds?

The other responders are accurate in their responses; a straight copy
shouldn't change a single bit of information. But the way I read your
subject line, I think you're asking about saving .jpg images, maybe at
something less than 100%. If you compress a file, that will give you
file size reduction, (something you mentioned in the subject). In that
case, every time you compress or re-save a file with a lossy format,
such as a jpeg file, yes it'll lose quality.

A test to show how this can happen, even if the jpg image is set to
write at 100%:

Open a jpg in Paint, make no change and save it with a slightly
different name. Now look at the properties. The size will be smaller
and you'll see some loss of quality as similar hues are blended together
into one color. Actually, you'll see the color change right after the
file is written to the hard drive. Do that a few times in a row, and
it'll really become obvious.

My own experience: I was editing a scanned calendar and publishing it
once a month and I soon found that if I edited the jpg image, the
quality deteriorated after each edit session. To get around this, I
saved a .bmp image of the image to edit. After each edit, I would also
save the file as a .jpg image and post that smaller image. If I had to
make another change, I'd load the .bmp image, edit it, save it, save as
jpg, and publish the jpg image.

hope this helps,

Merry Christmas.

--
Joe =o)
 
"Patrick Keenan" <test@dev.null> wrote:

>However, if the copy is also *compressed*, which will happen, for example,
>with WAV to MP3 conversion, there will be a loss in dynamic range, and that
>can certainly be considered a reduction in quality.

That depends on what kind of compression you're using. ZIP files, for
example, use lossless compression, so the restored file is *exactly*
the same as the original file. Image and sound formats, like Jpeg and
MP3, use lossy compression, because losing a few bits here and there
won't affect the quality of the image or sound. But if you use lossy
compression again and again on the same file, the inexactnesses will
add up over time, and the file will degrade.

For a normal copy operation on a computer file - command line "copy"
command or drag-and-drop - you're doing an exact copy, no compression,
no loss. You can do that as many times as you want to and still have
the exact same file.

--
Tim Slattery
MS MVP(Shell/User)
Slattery_T@bls.gov
http://members.cox.net/slatteryt
 
Zack <xxx> wrote:
> is it true that when you copy a file it starts to reduce it's quality?
> if so how do you prevent it from happening? does the same thing happen
> when you burn your photos or data to cds/dvds?

No. You're thinking about SAVING of certain image file types. Copying
is copying; no losses.
 
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