Publication Quality Graphics (Keynote to Photoshop/Illustrator)

Okay, installed the latest version of Keynote under High Sierra and did a very simple test. I dropped in three high resolution TIFFs, and an Illustrator file.

I then exported the page twice as a PDF. Once with the output quality left on Good, and the other as Best.

The main difference between them is the PDF saved using Best is 46.3 MB (the embedded TIFFs were saved to a much higher quality JPEGs). The standard Good output is only 916 KB. In other words, the TIFFs were bludgeoned down to junk (very highly compressed JPEGs). The Illustrator (vector) art remained as vector data.

Looking at both resulting PDFs in Acrobat, the quality difference is very obvious. The images in the smaller file have choppy edges (anything at an angle), are pixelated and soft.

Here's a section for comparison. Best on the right.

Edit: Oh! On top of that, if you're viewing the exported PDFs in Preview, you're not seeing a good rendition. Starting in Sierra (I think. May have been El Capitan), Preview applies anti-aliasing to the view of everything in PDF, whether it needs it or not. There's no option to turn this "feature" off. To get a truer view of your PDFs, use the free Acrobat DC Reader.

Since vector graphics don't have a resolution, it sounds like Keynote is rasterizing the images. Which is actually what you'd expect it to do since everything in a page has to be flattened down to one image in order to display it in a Keynote presentation.

It think it depends on the app. I can open an Illustrator .ai file in Preview and choose Print, then use the standard Save as PDF option in the bottom left drop down menu. Preview correctly preserves the Illustrator art as vector data in the PDF.

I'd have to install Keynote to see what it does differently.