An open community 
of Macintosh users,
for Macintosh users.

FineTunedMac Dashboard widget now available! Download Here

Topic Options
#51148 - 02/22/19 08:44 AM Apple compress function doesn't compress
ryck Offline


Registered: 08/04/09
Loc: Okanagan Valley
I am trying to reduce the size of a file that is well within the transmission limits of my ISP but is refused by a system that has a lower threshold. I've right-clicked on the file and chosen Compress "File Name". The system makes a zip file but it is the same size as the original. Tilt!

How do I get the OS compress function to reduce the file size?
_________________________
ryck

iMac (Retina 5K, 27", 2017), 3.4 GHz Intel Core i5, 8GB RAM, 2400 MHz DDR4
OS High Sierra 10.13.6
Canon MX710 Printer
Epson Perfection V500 Photo Scanner
Time Machine on 320GB OWC Mercury OTG Pro
Carbon Copy Clone on 500GB OWC Mercury OTG Pro

Top
#51149 - 02/22/19 08:53 AM Re: Apple compress function doesn't compress [Re: ryck]
grelber Offline


Registered: 08/05/09
Loc: North of 49th ||
More info required.

What sort of file? A text (eg, Word) document? A multi-format presentation?

Is it necessary that the recipient be able to manipulate the contents of the file? Or can it be a read-only file?

Maybe a straight PDF conversion would suffice?

Top
#51150 - 02/22/19 08:56 AM Re: Apple compress function doesn't compress [Re: ryck]
artie505 Online


Registered: 08/04/09
I use Keka for compression...lots of options with which to experiment, but first, what type of file are you trying to compress? Not all file types, e.g. PDFs, can be more than minimally compressed.
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

Top
#51152 - 02/22/19 01:40 PM Re: Apple compress function doesn't compress [Re: artie505]
ryck Offline


Registered: 08/04/09
Loc: Okanagan Valley
Originally Posted By: grelber
What sort of file?

Originally Posted By: artie505
Not all file types, e.g. PDFs, can be more than minimally compressed.

The file is a 16 page password-protected PDF which, I guess, provides the answer….it can’t be further compressed.

However, not all is lost. I found that it is quite easy in the Mac to split a PDF, so that’s what I did, and sent two smaller PDFs. And, before Ira asks smile , this is how easy it was:

1. Open the PDF with Preview.

2. Choose Thumbnail view to see all the pages in the left column.

3. Using Command-Click, select a group of pages.

4. Drag those to a folder or even just to the Desktop.

5. Using Command-Click, select the balance of the pages.

6. Drag those to the same place

Now you have two new PDFs, each comprised of half of the first.


Thanks for the tip on Keka….I’ll take a peek.
_________________________
ryck

iMac (Retina 5K, 27", 2017), 3.4 GHz Intel Core i5, 8GB RAM, 2400 MHz DDR4
OS High Sierra 10.13.6
Canon MX710 Printer
Epson Perfection V500 Photo Scanner
Time Machine on 320GB OWC Mercury OTG Pro
Carbon Copy Clone on 500GB OWC Mercury OTG Pro

Top
#51153 - 02/22/19 01:40 PM Re: Apple compress function doesn't compress [Re: grelber]
joemikeb Online
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
I'm with Grelber a lot more information is needed.

Using standard compression algorithms such a Zip, 7Zip, RAR, etc a 50% or better compression ratio is possible with pure text files, but if there are lots of graphics and/or audio it is entirely possible the compressed file will be larger than the original. Text compression algorithms like Zip, 7Zip, RAR, et. al. compress data by identifying repeating character strings in a segment of text and substituting pointers to the original string instead of repeating the string itself. Graphic and audio files have few or no such repeating strings and therefore are not compressed by these algorithms. In fact many compression utilities simply copy graphic and audio content rather than trying to compress them. Graphic and audio compression algorithms like JPEG, MPEG, ETC. are lossy and achieve compression by physically discarding some/much of the data which, of course would be unacceptable for text.

My solution for this situation is to place the data file in a public folder on an internet server and share it with the intended recipient(s). That handily gets around any email size restrictions/limits. You simply send the URL and the recipient downloads the file.
_________________________
joemikeb • moderator

Top
#51154 - 02/22/19 01:44 PM Re: Apple compress function doesn't compress [Re: joemikeb]
ryck Offline


Registered: 08/04/09
Loc: Okanagan Valley
Originally Posted By: joemikeb
Text compression algorithms like Zip, 7Zip, RAR, et. al. compress data by identifying repeating character strings in a segment of text and substituting pointers to the original string instead of repeating the string itself. Graphic and audio files have few or no such repeating strings and therefore are not compressed by these algorithms.

I'm guessing that's the answer. The file was one large PDF consisting of several pages of documents scanned in. I assume this means there would not be any of the character strings needed to reduce size through the repetition.

Just out of curiosity, I ran a quick test and compressed a text-only Pages file. It went from 180 MB to 147 MB. Thanks for the comprehensive and clear explanation....the penny has dropped. laugh


Edited by ryck (02/22/19 01:49 PM)
_________________________
ryck

iMac (Retina 5K, 27", 2017), 3.4 GHz Intel Core i5, 8GB RAM, 2400 MHz DDR4
OS High Sierra 10.13.6
Canon MX710 Printer
Epson Perfection V500 Photo Scanner
Time Machine on 320GB OWC Mercury OTG Pro
Carbon Copy Clone on 500GB OWC Mercury OTG Pro

Top
#51159 - 02/22/19 11:04 PM Re: Apple compress function doesn't compress [Re: ryck]
grelber Offline


Registered: 08/05/09
Loc: North of 49th ||
Originally Posted By: ryck
The file is a 16 page password-protected PDF which, I guess, provides the answer….it can’t be further compressed.
... I found that it is quite easy in the Mac to split a PDF, so that’s what I did, and sent two smaller PDFs. ...

You can do the same thing with Adobe Acrobat (if you've got it).

Top
#51160 - 02/23/19 06:25 AM Re: Apple compress function doesn't compress [Re: grelber]
ryck Offline


Registered: 08/04/09
Loc: Okanagan Valley
Yes, I was aware of that, and used to have Acrobat but got rid of it when I figured out that Preview does pretty much everything I need to do with PDFs. I also like using a piece of software that is essentially an extension of the OS.
_________________________
ryck

iMac (Retina 5K, 27", 2017), 3.4 GHz Intel Core i5, 8GB RAM, 2400 MHz DDR4
OS High Sierra 10.13.6
Canon MX710 Printer
Epson Perfection V500 Photo Scanner
Time Machine on 320GB OWC Mercury OTG Pro
Carbon Copy Clone on 500GB OWC Mercury OTG Pro

Top
#51165 - 02/23/19 09:34 AM Re: Apple compress function doesn't compress [Re: ryck]
Ira L Offline


Registered: 08/13/09
Loc: California
It is possible to compress a PDF in Preview. I have done it many times and the results vary in terms of savings and quality.

*In the Preview app on your Mac, open the PDF, then choose File > Export.

*Click the Quartz Filter pop-up menu, then choose Reduce File Size.
_________________________
On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.14.x,; iPhones, iPods and iPads galore!

Top
#51166 - 02/23/19 09:54 AM Re: Apple compress function doesn't compress [Re: Ira L]
artie505 Online


Registered: 08/04/09
Originally Posted By: Ira L
...the results vary in terms of savings....

I just experimented with the first PDF I could find, and ZIP reduced it by about 10%, 7Z reduced it a bit further, and Preview/File/Export increased it by about 50%.

Vary, indeed. crazy
_________________________
The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

Top
#51168 - 02/23/19 10:51 AM Re: Apple compress function doesn't compress [Re: Ira L]
ryck Offline


Registered: 08/04/09
Loc: Okanagan Valley
Originally Posted By: Ira L
....the results vary in terms of savings and quality.

I had a little different experience than artie. The compression was quite dramatic....from 11.7 MB down to 409 KB. However, when I double-click opened the compressed file it didn't appear to unpack and I was looking at very blurry text.


Edited by ryck (02/23/19 10:53 AM)
_________________________
ryck

iMac (Retina 5K, 27", 2017), 3.4 GHz Intel Core i5, 8GB RAM, 2400 MHz DDR4
OS High Sierra 10.13.6
Canon MX710 Printer
Epson Perfection V500 Photo Scanner
Time Machine on 320GB OWC Mercury OTG Pro
Carbon Copy Clone on 500GB OWC Mercury OTG Pro

Top
#51170 - 02/23/19 01:27 PM Re: Apple compress function doesn't compress [Re: Ira L]
joemikeb Online
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
Originally Posted By: Ira L
It is possible to compress a PDF in Preview. I have done it many times and the results vary in terms of savings and quality.

*In the Preview app on your Mac, open the PDF, then choose File > Export.

*Click the Quartz Filter pop-up menu, then choose Reduce File Size.

Remember that a scanned PDF file is an image just as a JPEG is an image. Image compression algorithms do their thing by discarding data. The variation in results are a function of the initial scan resolution (how much data you start with) and the compression level (how much of the original data is discarded in the compression process).
_________________________
joemikeb • moderator

Top
#51313 - 03/12/19 09:38 AM Re: Apple compress function doesn't compress [Re: ryck]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
Originally Posted By: ryck
The file is a 16 page password-protected PDF which, I guess, provides the answer….it can’t be further compressed.


No further information is required

That means it's encrypted. Encrypted data cannot be compressed. The End.
_________________________
I work for the Department of Redundancy Department

Top

Moderator:  alternaut, dianne, dkmarsh