To get the built-in Reduce File Size Quartz Filter to reduce file size, I also have to check “Optimize images for screen”.

One of the most popular pages on my site is how to create a Reduce File Size Quartz filter. Sadly, while it appears to be still recommended by many people, it hasn’t worked for me for a long time. But I recently decided to write a color cookbook and I wanted to make the PDF available for download.

I don’t like having multiple sources for multiple destinations. That way lies madness. I want the same source to provide for different destinations. But the file destined for print¹, because this book is focused as much on the images as on the recipes, was large even for modern downloads. If it turns out to be a tenth as popular as Quality Reduced File Size I don’t need people downloading hundreds of copies of a 34 megabyte file every day.

So I decided it was time to take a look at why Quartz filters stopped working so long ago, or at least how to get them working again. To be honest, I’m still not sure what’s going on. But I was able to get the stock Reduce File Size filter working again.

The executive summary is that I have to turn on Optimize images for screen if I want Reduce File Size to actually reduce file size. Read further for what I discovered in greater detail, as well as advice if you have multiple copies of your aging custom quartz filters.

First, Quartz filters no longer show up at all on Print, even from Preview. I have to open the PDF in Preview and choose File:Export to get the list of filters. Even then, though, if I just choose “Reduce File Size”, the resulting file is always exactly the same size as the starting file.

Apple’s help page says that, to reduce file size, you have to:

Do one or more of the following:

• Compress PDF graphics to presentation quality: Select the “Optimize images for screen” checkbox.
• Convert all graphics to JPEG format: Select the “Save images as JPEG” checkbox.

The various file size changes (or non-changes). “O” is for “Optimize images”, “S” for “Save… as JPEG”, and “R” for “Reduce File Size” Quartz Filter.

Their instructions make no mention of the built-in Reduce File Size filter, let alone custom filters.

Their instructions also don’t work. Neither of those options, for me, reduces the file size at all. Nor did choosing both of them reduce the size of my large file.

But, choosing both of them as well as Reduce File Size did exactly as expected, or even better: it reduced the file size, and dramatically, while maintaining quality images throughout.

In fact, after some experimenting, the critical checkbox is Optimize images for screen. If that checkbox is checked, then Reduce File Size will reduce the file size. If both “Optimize images for screen” and “Save images as JPEG” are checked it reduces the size slightly more. But only very slightly.

Here are the sizes I got from my 34 megabyte cookbook PDF with several large images:

I have no real idea why this is. My conjecture is that without Optimize checked, the code for reducing file size is ignored because the images aren’t being changed. Optimize triggers an image change because (in my conjecture) higher-resolution images are being reduced to screen resolution.

Regardless, this does allow me to use the Reduce File Size quartz filter again. There’s a caveat, though. While custom filters also result in a reduced file size, it is the same reduced file size as the built-in filter, regardless of where I put the slider. The slider appears to be superfluous now.

ColorSync Utility. The slider for compression is still there and can be adjusted. It doesn’t appear to have any effect on my system.

One odd difference between the built in Reduce File Size and custom versions is that, for custom filters, if I leave “optimize” unchecked and “save as JPEG” on, there is a very minor reduction in size. In my case, by about two percent. The large source file goes from 34 megabytes to 33.3 megabytes. Again, it’s the same reduction regardless of where I move the slider.

On the plus side, however, it doesn’t look like custom filters are needed. The default Reduce File Size works well for screen viewing. It no longer reduces image quality so much as to make some images completely unviewable.

As a potentially useful aside, for those who have been using custom quartz filters forever like I have, there have been at least two places that macOS has stored them. In my case, they’ve ended up in two places. Either I copied them over trying to get them to work (very probable, since I mention exactly this in Quality Reduced File Size), or macOS copied them over at some point, but recently this has meant that both incarnations show up in the Quartz Filter drop-down of Preview’s File:Export.

As it turned out, both had also become write protected over the years. ColorSync Utility wouldn’t let me change or delete either one. Again, I don’t know who did that, me or macOS, but I ended up deleting both of them in the Finder and then recreating one using ColorSync Utility. Since I only had two doubled filters—Reduce File Size Medium and Reduce File Size High Quality—this wasn’t a hardship.

The two folders are both in ~/Library. They are ~/Library/Filters and ~/Library/PDF Services. They may also be in the system-wide equivalents, /Library/Filters and /Library/PDF Services. The current location where ColorSync Utility stores custom filters, under Sequoia, is ~/Library/Filters. The system-wide defaults are in /System/Library/Filters. They’ll be named with the same name you give them in ColorSync Utility, with a .qfilter extension.