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How to decrease .pdf size without losing quality [Resolved]

Background

I want to decrease size of the .pdf filled with images. In Preview in can be dome through Export and set Quartz Filter-> Reduce File Size before saving.

Preview-Export

Problem

The file indeed decreased from ~30MB to 0.37MB.

But the result has such poor quality that images are barely readable.

Question

I saw an examples of using Image Magic to achieve that - but can it be done by Preview without any external software?


Question Credit: michalczukm
Question Reference
Asked March 25, 2019
Posted Under: Apple
21 views
6 Answers

The problem is - the default filter used during conversion has very low conversion settings.

Thankfully, a custom filter can be added.

Adding custom filter step by step

  1. Create new directory (if you don't have it) - /Library/Filters
  2. Add there new filter file with unique filter - f.e. Reduce Size with good quality.qfilter
  3. The file should contain XML with new filter - you can base on the /System/Library/Filters/Reduce File Size.qfilter file or use my below example. Change compression setting, image size and add unique display name for your filter.

Filter file structure/example

I marked key settings by comments.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Domains</key>
    <dict>
        <key>Applications</key>
        <true/>
        <key>Printing</key>
        <true/>
    </dict>
    <key>FilterData</key>
    <dict>
        <key>ColorSettings</key>
        <dict>
            <key>DocumentColorSettings</key>
            <dict>
                <key>CustomLHSCorrection</key>
                <array>
                    <integer>8</integer>
                    <integer>8</integer>
                    <integer>8</integer>
                </array>
            </dict>
            <key>ImageSettings</key>
            <dict>
                <key>Compression Quality</key>
    <!-- ====== Set your custom quality <0,1> ======= -->
                <real>0.75</real>
                <key>ImageCompression</key>
                <string>ImageJPEGCompress</string>
                <key>ImageScaleSettings</key>
                <dict>
                    <key>ImageScaleFactor</key>
    <!-- ====== Set your scale factor <0,1> ======= -->                 
                    <real>0.75</real>
                    <key>ImageScaleInterpolate</key>
                    <true/>
    <!-- ====== Set what sizes your images can reach ======= -->                    
                    <key>ImageSizeMax</key>
                    <integer>1684</integer>
                    <key>ImageSizeMin</key>
                    <integer>1200</integer>
                </dict>
            </dict>
        </dict>
    </dict>
    <key>FilterType</key>
    <integer>1</integer>
    <key>Name</key>
<!-- ====== Set unique display name for your filter ======= -->
    <string>Reduce Size Good Quality</string>
</dict>
</plist>

Result

Select your new filter when exporting file.

enter image description here


Helpful articles:


credit: michalczukm
Answered March 25, 2019

You can use this website: https://smallpdf.com/compress-pdf to shrink PDFs to a really small size. The PDF quality is still really good even after the compression.


credit: Amit Kulkarni
Answered March 25, 2019

As per michalczukm answer, a quartz filter can solve this. I had created my own and shared it on Github. You can install it easily with a single command line. It doesn't install any software, just the quartz filter only.

https://github.com/superman-lopez/compressjpeginpreview


credit: Superman.Lopez
Answered March 25, 2019

You can create your own Filter to reduce the image data size in the PDF, using Apple's built-in ColorSync Utility. Then select the Filter in Preview's Export.

(NB: For some reason "Export As PDF" doesn't show the Filters, but Export, choosing PDF as the file format, does.)

enter image description here


credit: benwiggy
Answered March 25, 2019

If you have a pdf which is version 1.6 or 1.7, you can use the duplicate setting in Preview. Preview will save the file as a 1.4 pdf and save about 50% in file size. As far as I can tell there is no loss of quality. No need to use the export - reduced file size unless you want further savings.


credit: jmh
Answered March 25, 2019
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