For optimize you can specify a few parameters. For each image in the PDF, DynaPDF will check the display resolution of the image. That is not the resolution stored in some metadata with the image, but the actual size the image will be displayed. You can specify the minimum resolution for images to be checked independently for Color, grayscale and 1 bit images. Next you define the resolution you want as maximum for the output images. For example you want to scale down all images with more than 100 dpi and reduce them to maximum 150 dpi. For the filter parameter you can specify the compression you want, e.g. JPEG. Converting images from Flate compression to JPEG with same or lower resolution will of course reduce the file size.
When optimizing PDFs, we can remove private data, invisible paths and create new link names. This further reduces size down and rebuilds the structure of the PDF. While doing the optimize we fix problems in PDF files automatically. Some PDFs which showed error messages when opening in Adobe Reader now open without errors.
Here an example:
The test PDF optimize-before.pdf is created with FileMaker 15 from the product catalog example with a few pictures. Than printed to PDF in FileMaker. Of course you can use whatever test PDFs you like for your own tests. Now we run through and let DynaPDF limit image resolution to 150 dpi. The new PDF optimize-after.pdf is much smaller. From 686 KB down to 89 KB (87% saved).
or when we scale them up at 200%:
We can extract the images and see that FileMaker placed a 816x612 Pixel big JPEG file (optimize-image-before.jpg) there. DynaPDF replaced that with a 206x154 Pixel big (optimize-image-after.jpg). I don't think you see the difference at the target size in the PDF. And 150 dpi is quite good for reading on screen and sending via email. FileMaker probably uses 600 dpi here to make sure it looks good when printing.
If you join FileMaker DevCon in Las Vegas, please visit our booth to try compression on your test PDFs!