Does Compress Old Files in Disk Cleanup affect photos?

Was wondering if this function in Windows affects photo files.

Thanks.

 

It is a losses compression so no detail is lost, but they will take
longer to load.
Also jpeg photos will really not compress any more then they are so
there is little point in using window to compress them.

Scott

 

It is a losses compression so no detail is lost, but they will take
longer to load.
Also jpeg photos will really not compress any more then they are so
there is little point in using window to compress them.

Scott

I don't understand the above. If I take a jpeg photo that was saved with
moderate compression so the file size is say, one megabyte, and I resave it
with more severe compression, so the file size is say, 1/2 megabyte, isn't
that compressing it more?

 

The OP was talking about Windows routine to compress files, this is a
lossless compression and since jpeg files have already gone through a
final stage of lossless compression there is nothing to be gained.
Try making a zip file out of a jpeg image and you will see that it
does not shrink the file much very much, only a very small part of a
jpeg file is not already compressed. A quick test shows that I am
seeing much less then a 1% reduction in the size of the file when I do
this.

Scott

 

The OP was talking about Windows routine to compress files, this is a
lossless compression and since jpeg files have already gone through a
final stage of lossless compression there is nothing to be gained.
Try making a zip file out of a jpeg image and you will see that it
does not shrink the file much very much, only a very small part of a
jpeg file is not already compressed. A quick test shows that I am
seeing much less then a 1% reduction in the size of the file when I do
this.

Scott

Ah.....Thank you....The key phrase here is, "Lossless compression"......I
never expected any compression to be lossless. This seems to me to be like
getting something for nothing....I'm always glad to get a free lunch....:^)

 

Lossless compression works by discarding unnecessary information and
encoding what's left. For example, normal English text can be written
with 52 letters, a space and a few punctuation characters: perhaps 60
characters in total. A byte contains 8 bits and allows for up to 256
characters, but if you're using only 60 characters you can represent
that with 6 bits, which means you can cram one and a third characters
into a byte or four characters into three bytes. The text ends up
taking only 3/4 as much space, but no information has been lost.

Real lossless compression is more complex than that: a good algorithm
would recognise the frequent use of the sequence "compress" in this
message and replace it with a single shorter code, and that means that
some popular compression algorithms can compress text by around 80%.
However, if something has already been compressed there's little or
no redundant information left to remove so a second compression is
ineffective.

One of the features of lossless compression is that for every lossless
algorithm there will always be some data that can't be compressed at
all. This doesn't stop people from trying to find a way around this
restriction even though it's been proven impossible. See section 9.2
of http://www.faqs.org/faqs/compression-faq/part1/section-8.html for
details.

 

5-level Baudot gets it done in 32 characters - well 2 sets of 32 with a
shift character to get between sets. With 5 character words it
works out to ~25 bits/word.

Static dictionary compression gets it down to ~14 bits/word
using a 16,000 word vocabulary.