Disk Cleanup: can I uncompress compressed files?

We have a lot of photos which are already compressed in .tif format. Having
carried out a Disk Cleanup recently and allowed compression of older files,
I am now concerned that further compression of .tifs will have degraded my
photos. Of course, if this is the case, then the damage has already been
done, and, in future, I will not allow compression by Disk Cleanup.
Meanwhile, can I get my photos back to non-archived state, please? Just
opening them doesn`t change anything, in that the file names remain in blue.

Incidentally, I think it would be nice to be able to exclude certain file
types, or certain folders, from compression when using that facility in Disk
Cleanup.

How much hard drive do you have? How much is free? And how much did
the compression of old files save you?

If it did degrade the files, then old .exe files would be useless when
restored.

Out of curiosity, can it tell the difference between a file which is
smaller when compressed and one which isn't? I've never seen a message
such as "No point compressing that file, friend" and everything I've
ever tried to compress has ended up with the green "compressed"
indicator. I've known many systems where the compressed files sometimes
ended up larger

If I knew the answer to this, and it was what I hoped, then I would
probably turn compression on my entire \backup tree, for example.

Although it might be able to do this, there is no built-in capability
to do so. So the practical answer to your question is no.

The normal result of compressing an already-compressed file is to make
it slightly larger. You get no extra compression, but you get the
overhead the extra layer of compression creates.

No, that's not the case. The kind of compression done by Disk Cleanup
is lossless, and doesn't hurt photos or any other files in any way.
When the files are uncompressed, they will be identical to what they
were before.

Exactly. And as far as this kind of compression is concerned, it can't
tell the difference between an exe file and a tif.

I have 82GB spare HD capacity. I only ran Disk Cleanup on advice after I
installed XP SP3 and thought that the system had slowed down. Now I wish
that I hadn`t taken that advice. Too late, though. I cannot remember how
much space was saved but it probably wasn`t all that significant anyway -
which, I would guess, is probably the point you are quite rightly making.

If I cannot return our photos to a non-archived state, I suppose I could
open each one and Save As with a different name, then delete the old ones,
but it`s a daunting task. Still, if the compression format in Disk Cleanup
*is* totally lossless, and repeated opening and closing of the files will
not degrade the images at all, I probably won`t bother. I have looked
online, but couldn`t find anything that completely reassured me.

I sent off my earlier post before I saw these other replies.

NO way could I leave this one slide.
1). Click Start
2). Click Run and type “cmd” to open a command prompt
3). Type “cd \” at the prompt to goto the root directory
4). Type “compact /u /s /a /q /i *.*” to decompress all files in all directories
You can run that command in ANY directory and it will decompress.

thirtysix you don't know how much that post may have helped me out. I've been looking for a way to do this for weeks. My company has outsourced it's IT to India and I am one of the few engineers left on site. They have recently decided to run the disk cleanup wizard on desktops and servers compressing all sorts of files. I would just like to point out if anyone thinks it is a good idea to click the compress old files checkbox when doing this then DON'T! MS should rename that checkbox to 'Cause problems and make my computer run slowly'. I shall give this command a try!

FYI running the wizard with this checkbox will indiscriminately compress any files over a certain age. This includes system files and .dll files. It is a really bad idea. Compression should only be used for files that are rarely accessed and that are not accessed over a network.

I feel your pain.
Once you've uncompressed run defrag a bunch of times untill the utility breezes through in a couple of seconds. There's no way to know your situation, but there are several freeware defrag solutions that work much better than the low rent option M$ has as standard.
For those whom aren't savvy, any file that's compressed is uncompressed "on the fly" by the system. On lower end systems you might see a performance hit because of this, on top end systems it is negligible.

Thitysix, you are a bloody wizard, i just made a batch file of this to add to my toolkit. So many people do this thinking it will make space on their system only to find it becomes too slow to use afterwards!
This little gem will save me time, many thanks.