Copwatch: Filtering Dpi Tried Or Appropriate Or Proportionate ! http://newish.info/76684-copwatch-filtering-dpi-tried-or-appropriate-or-proportionate
Compress PDF files on a Mac with Quartz Filters
You want to shrink the file size of a PDF document, but also want full control over its visual quality? Continue.
There are many ways of achieving this, but the method I’m about to show you doesn’t require any new software, which I always like.
So go ahead and open up the document in Preview. Head to File ->Save as…
Then you click on “Quartz Filter” and finally on “Reduce File Size”. Go ahead and save that document and take a look at it. If you’re happy with the quality you see, you’re done. However many people aren’t happy with this option because it scales down the pictures in your PDF file to 50%, which makes them look blurry. So here is the fully customizable way to do it.
In Spotlight type “ColorSync” and open up the “ColorSync Utilities”.
Click on the “Filters” tab and create a new one by clicking the “+” icon. For our purposes let’s name it “150DPI”. Click on the downwards pointing arrow on the right and go to “Add Image Effects Component” -> “Color Image Sampling”.
Under “Resolution:” enter “150”. This will be our DPI value.
DPI stands for “Dots Per Inch” which describes the amount of pixels over the length of 1 inch. If you’ve never worked with this unit let me give you a few examples:
300dpi - good print quality - amazing screen quality
150dpi - acceptable print quality - good screen quality
75dpi - low print quality - acceptable screen quality
I like to use 150dpi because it’s looks lossless on a computer screen and still pretty good on paper. You can choose whatever value you want but remember that by doubling the dpi value all pictures in your document will be 4x larger. If you’re still not sure what to choose, try a few different settings and judge the quality of your output. You can create as many filters as you want.
The advantage of changing the dpi value instead of the size in percent is that we directly set the visual quality. By using the size in percent it will always depend on how large the picture was originally and how large you scaled it in your document, which doesnt make it very useful.
Close the ColorSync Utilities and open the PDF file that you still want to resize in Preview. Again head to File -> Save as… -> Quartz Filter, but now you’ll see a new option named “150DPI”
Select that option and save your file. You might want to print it as well to have a look on the quality on paper.
And that’s it! A little pain to set up, but once you have it, it’ll be right there at you finger tips, built into Preview.
