How to reduce image's file size in Preview?

Question

I am in Preview Version 5.0.3 (504.1).  I have a PDF file that is 3.7 meg. in size.  That is a big large for what I want to do with it.  I would like to reduce its size to something a bit more manageable.   The Preview Help gives these instructions:To reduce an image’s file size without changing its dimensions:Choose Tools &gt; Adjust Size.Select “Resample image.”Enter a smaller value in the Resolution field. My problem is that in my open window for this file the "Adjust Size" tool is dimmed.  I cannot choose that tool as instructed.   Does anyone know why and how to get Preview to reduce the size of a PDF file?

andyBall_uk · Answer

try File-Save As...&amp; choose format:pdf    quartz filter:reduce file sizepick another name to check the results - there&#x27;s no undo

cbpg · Answer

Thanks .. but the quality dropped too much.. so i found a cumbersome but good way around it ... i exported the file to jpeg then put each page into Pages and then turned that into a PDF.. quality was great and the size very manageable

kwagarratt · Answer

Hi cbpg.I sympathise. This is a major failing on the part of Apple. The ‘Reduce File Size’ command on the Quartz Filter dropdown in the Preview ‘Save as PDF’ window gives such poor quality that it is pretty much unusable.For some years I have modified my System Files as suggested by a genius on this Forum whose name I have long forgotten, so that the drop down now gives me four different options for reducing file size with varying quality loss. It worked great.Every time Apple produced a new OS I had to do the modification again, which was no problem until El Capitan when Apple prevented users from modifying their System Files.Now I have worked out how to do it again, and am back in business.I borrowed another Mac, put mine into Target Disk Mode and modified the files on mine using the borrowed machine. It worked a treat. (Mine is a 2010 machine with FireWire800 and the borrowed one is a newer one with Thunderbolt, so I had to buy a Thunderbolt-to-Firewire adaptor from Apple for an arm and a leg, but it worked fine.)To do the modification you:Open your Hard driveGo to: System -&gt; Library -&gt; FiltersExtract the "Reduce File Size.qfilter" file to work on at your leisure.Make three copies of the file.Using TextEdit, modify the last part of the code in each file. (You may have to drop the files into the TextEdit icon to get it to open them.)First copy should now read:&lt;key&gt;Compression Quality&lt;/key&gt;  &lt;real&gt;0.25&lt;/real&gt;  &lt;key&gt;ImageCompression&lt;/key&gt;  &lt;string&gt;ImageJPEGCompress&lt;/string&gt;  &lt;key&gt;ImageScaleSettings&lt;/key&gt;  &lt;dict&gt;  &lt;key&gt;ImageScaleFactor&lt;/key&gt;  &lt;real&gt;0.5&lt;/real&gt;  &lt;key&gt;ImageScaleInterpolate&lt;/key&gt;  &lt;true/&gt;  &lt;key&gt;ImageSizeMax&lt;/key&gt;  &lt;integer&gt;842&lt;/integer&gt;  &lt;key&gt;ImageSizeMin&lt;/key&gt;  &lt;integer&gt;128&lt;/integer&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;key&gt;FilterType&lt;/key&gt;  &lt;integer&gt;1&lt;/integer&gt;  &lt;key&gt;Name&lt;/key&gt;  &lt;string&gt;Reduce File Size Good&lt;/string&gt;&lt;/dict&gt;&lt;/plist&gt;Second copy should now read:&lt;key&gt;Compression Quality&lt;/key&gt;  &lt;real&gt;0.5&lt;/real&gt;  &lt;key&gt;ImageCompression&lt;/key&gt;  &lt;string&gt;ImageJPEGCompress&lt;/string&gt;  &lt;key&gt;ImageScaleSettings&lt;/key&gt;  &lt;dict&gt;  &lt;key&gt;ImageScaleFactor&lt;/key&gt;  &lt;real&gt;0.5&lt;/real&gt;  &lt;key&gt;ImageScaleInterpolate&lt;/key&gt;  &lt;true/&gt;  &lt;key&gt;ImageSizeMax&lt;/key&gt;  &lt;integer&gt;1684&lt;/integer&gt;  &lt;key&gt;ImageSizeMin&lt;/key&gt;  &lt;integer&gt;128&lt;/integer&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;key&gt;FilterType&lt;/key&gt;  &lt;integer&gt;1&lt;/integer&gt;  &lt;key&gt;Name&lt;/key&gt;  &lt;string&gt;Reduce File Size Better&lt;/string&gt;&lt;/dict&gt;&lt;/plist&gt;And the third copy thus:&lt;key&gt;Compression Quality&lt;/key&gt;  &lt;real&gt;0.75&lt;/real&gt;  &lt;key&gt;ImageCompression&lt;/key&gt;  &lt;string&gt;ImageJPEGCompress&lt;/string&gt;  &lt;key&gt;ImageScaleSettings&lt;/key&gt;  &lt;dict&gt;  &lt;key&gt;ImageScaleFactor&lt;/key&gt;  &lt;real&gt;0.5&lt;/real&gt;  &lt;key&gt;ImageScaleInterpolate&lt;/key&gt;  &lt;true/&gt;  &lt;key&gt;ImageSizeMax&lt;/key&gt;  &lt;integer&gt;3508&lt;/integer&gt;  &lt;key&gt;ImageSizeMin&lt;/key&gt;  &lt;integer&gt;128&lt;/integer&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;/dict&gt;  &lt;key&gt;FilterType&lt;/key&gt;  &lt;integer&gt;1&lt;/integer&gt;  &lt;key&gt;Name&lt;/key&gt;  &lt;string&gt;Reduce File Size Best&lt;/string&gt;&lt;/dict&gt;&lt;/plist&gt;You might also want to retain the original file as a fourth option by modifying the ‘name’ part of it thus:&lt;key&gt;Name&lt;/key&gt;  &lt;string&gt;Reduce File Size Poor &lt;/string&gt;Make sure all the file extensions read .qfilter rather than .txt. (TextEdit tends to save them as .txt.)Now set up your machine in Target Disc Mode and insert those four files into the &#x27;Filters&#x27; folder in place of the original file using the borrowed machine. Apple can&#x27;t stop you!When you save a file as PDF in Preview the ‘Quartz Filter’ drop-down should now give you four options for reducing file size.I have seen other code modifications which give multiple other levels of reduction, but these are the four I have used for years and they seem to work well. Most of the time the &#x27;Good&#x27; compression setting is what I need.Why on earth don’t Apple do this themselves?Hope that helps. And thanks again to that unnamed code-writer!

kwagarratt · Answer

Forgot to say in my post:Name each copy of the filter file differently, thus:Reduce File Size goodReduce File Size BetterReduce File Size BestReduce File Size Poor...in line with the naming stream at the bottom of the code

CaptainJack67 · Answer

Any chance someone knows how to change preview 5.0.3 to run at 32 bit?