Archive/ZIP

[iGary]

OK, so I have to zip something into an archive file, which I have done - whay is it not any smaller then the original file?

*feeling stupid*

 

[iMeowbot]

What kind of file was the original? If it's a format that does compression on its own, zip won't help much, and in pathological cases can even result in a larger file.

 

[iGary]

What kind of file was the original? If it's a format that does compression on its own, zip won't help much, and in pathological cases can even result in a larger file.

8 tiff files.

 

[iMeowbot]

Adobe-style TIFFs normally use a compression algorithm called deflate, which is exactly the same one zip uses. Ending up with the same size would be normal.

 

[Mitthrawnuruodo]

Was the tiff files already compressed?

Many lossless compression algorithms will just add a bit when they encounter files they are not able to compress.

Here's the explanation from gzip.org:

Compression is always performed, even if the compressed file is
slightly larger than the original. The worst case expansion is
a few bytes for the gzip file header, plus 5 bytes every 32K block,
or an expansion ratio of 0.015% for large files. Note that the actual
number of used disk blocks almost never increases.

 

[iGary]

Was the tiff files already compressed?

Many lossless compression algorithms will just add a bit when they encounter files they are not able to compress.

Here's the explanation from gzip.org:

Compression is always performed, even if the compressed file is
slightly larger than the original. The worst case expansion is
a few bytes for the gzip file header, plus 5 bytes every 32K block,
or an expansion ratio of 0.015% for large files. Note that the actual
number of used disk blocks almost never increases.

No compression was used on the tiff files at all. Zero.

 

[Mitthrawnuruodo]

No compression was used on the tiff files at all. Zero.

That's odd...

What did you use to compress them? Finder's built-in Create Archive?

 

[iGary]

That's odd...

What did you use to compress them? Finder's built-in Create Archive?

Yep, sure did.

 

[jsw]

Try this:

Open up Terminal.

Type in

zip -9 pic.zip

with a space after the "pic.zip".

Find your file in Finder and drag it to the Terminal window.

Hit "return".

You should now have a much smaller file, named "pic.zip", in your home folder.

Of course, use any file name you like, and you can add a directory path so it doesn't end up in your home folder.

You can also just type in

zip -9

with a space after the "-9", then drag the file onto Terminal, back up to delete the space it adds after the file name and append ".zip " [note the space] then drag the same file over again, so your Terminal line woould look something like this:

zip -9 /Users/iGary/Photos/MyBigToe.tiff.zip /Users/iGary/Photos/MyBigToe.tiff

which will add the zip file in the same place as the original TIFF file.

The "-9" means to compress it as much as possible.

 

[Mitthrawnuruodo]

Yep, sure did.

Hmmm... I don't have a good explanation for you. I have had some trouble with the built-in compression earlier (and used Terminal, in stead) but some simple tests now compressed some small but uncompressed tiff files in half when I used the built-in Create Archive in Finder, and I only saved a few bits by making a zipped tar in Terminal...

There is the chance that the images are so complex that the zip algorithm cannot find redundant bits to get rid of, but for 8 images...???

BTW, nice stache...