The version of Preview in OS X 10.5 has some nice additions to its 10.4 predecessor, including more annotation abilities for PDFs. What I didn’t know, until very recently, is that you can also annotate JPEGs, TIFFs, and other non-PDF images. You might not think that’s the case, because if you open such an image in Preview, while the Tools -> Annotate menu is active, all the sub-menus beneath Annotate are grayed out. How can you use a non-active menu item?
Once you’ve placed an annotation, you can also make modifications to it. For the shape annotations, use the minus (-) and equal (=) keys to make the shape’s lines thinner or thicker. To change the color of a shape, bring up the color picker (Shift-Command-C, or View -> Show Colors). Select the color you’d like to use, and the shape will instantly change to reflect your selection.
If you’re working with the Note tool, the color picker will change the color of the note’s text. You can also change the font by using the Fonts panel (Command-T or View -> Show Fonts). Select the text within the note, then choose the font face and size you’d like to use. (You can also change the size of the font in the note using the minus and equal signs.) It may look like you can also use the buttons at the top of the Fonts panel (underline, strikethrough, shadow, etc.), but you can”t—while those features will show up as you edit, they’ll vanish as soon as you click elsewhere in your Preview document.
If you’re annotating a PDF, you can’t use the line thickness tools, nor can you change the font face or size of your notes. About the only thing you can do is change the color of shapes on a PDF, using the color wheel. (I’m not sure why annotating is more limited with PDFs, but it is—if you know why this might be the case, I’d love to hear an explanation.)
I assume the Annotation menu should be enabled when working with non-PDF images, and that it’s simply a bug that will be addressed in a future update—otherwise, it seems odd to hide such useful features behind a toolbar button that’s not on the default toolbar.