At first Preview landed in my lap exclusively. Someone had shimmed in some code to open Quicktime image types that NSImage (NeXTStep, AppKit) did not recognize — "BMP" just as an example.

I was told, "Hey, we have a rich PDF API/SPI in CoreGraphics (Quartz2D) maybe you can beef up our PDF support in Preview."

PDF at that time was quickly rasterized (by AppKit) and really treated no differently than, say, a multi-page TIFF file in Preview.

As I started to switch over to rendering PDF's using CoreGraphics rather than NSImage, another engineer (Werner) took over the image side of Preview.

For a while then it was a team of two — me and Werner. Werner did the image side (but also owned and had responsibility for ImageIO) and I did the PDF side (I eventually wrote PDFKit but also had things like the Displays Prefs pane, some Color Sync stuff as my other responsibilities as well).

Werner is smarter than me though so where there were shared resources in Preview (like the toolbar, for example) often Werner handled that.

What I gave above is more or less the direction we were given — so there was a good deal of autonomy. I think everyone sort of had their hands full just trying to get a new graphics system up and running and to move functionality over from System 9 to OS X such that Werner and I were free to just add the stuff we wanted.

Initially I think we tried to keep some commonality — if images could be rotated, I would try to also rotate PDFs. Image zoom in/out? PDF zoom in/out.

But when I added text handling (text selection, search) we kind of acknowledged that the two really were separate beasts. I was surprised later though when the same annotations I had added to support PDF also were added as mark-up tools to images (I was no longer on the team then as I recall).

Preview eventually went to its own team though and the engineers working on it did not have other duties/distractions like Werner and I. This is when signatures, instant-alpha, and other niceties were added.

I definitely enjoyed the years Werner and I were on it and we could just add "cool stuff" we wanted. I remember someone asking for the "blank page" feature — where you can insert a blank page into a PDF – it allows you to play with even/oddness (front/backedness) of pages when printing 2-up. It was cool so we added it.

I like to point out that "we" were the users of the app as much (or more so) than some manager up the chain. To that end, I always felt we more or less knew what users wanted.

I think eventually the designers came to use Preview quite a bit and so had their own suggestions but they certainly weren't standing in our way early on.