Yet I think few users realize that the settings in this dialog box govern some other rasters generated by Illustrator, not just the ones from the Effect menu. (I have no idea why it's a menu command — it should be a Preferences setting.) If you think you never have to choose Document Raster Effects Settings because you're not using any Effects, think again.
Newbie Review: What's a Raster Effect
Graphic Design 101 tells us that Photoshop is a "paint" program, and Illustrator is a "drawing" program. You paint with colored pixels in Photoshop, and in Illustrator you draw paths which you fill and stroke with color. The technical term for these two general types of image formats are raster (paint) and vector (paths). Rasters give you soft edges that fade into the background and are hard to edit, vectors give you hard edges that are easy to edit.
However, in Graphic Design 201, we learn that the software world is not quite so delineated. You can draw with vectors in Photoshop (the Pen tool and vector shape layers are two examples), and you can create rasters in Illustrator (a common one is Effects > Stylize > Drop Shadows).
Raster Resolution Settings
Unlike vectors, which are resolution independent, the output quality of raster images depends upon their resolution. When you're creating a raster image, you need to tell the program how large the pixels should be — that is, how many pixels can fit in an inch, aka ppi (pixels per inch). Raster images for a web page need only be 72 ppi (relatively large pixels), but those for high-res print output need to be more like 225-300 ppi so they don't look pixellated (the tell-tale stair-stepping) in the printed output.
In Photoshop, we're asked for the ppi resolution right up front in the New document dialog box, but not in Illustrator (another missed opportunity, in my opinion). Yet, as I mentioned earlier, the default resolution for rasters in Illustrator is 72 ppi, as it has been for ages, even though most Illustrator artwork is destined for print, not web sites.
Why, Adobe? Is it because you think Illustrator users seldom, if ever, create drop shadows or blurs? The engineers like to embed land mines in the program for sport? Tis a puzzlement.
So, savvy Illustrators know that if they use any of the Effects that create rasters — such as drop shadows, feathers, or glows — and their artwork is destined for print, they need to change the resolution for these raster effects before saving the file a final time. It's easy, just go to the Effects > Document Raster Effects Settings dialog box and click the "High (300 ppi)" radio button, or enter a custom resolution suitable for your project.
Even if you inadvertently created all your raster effects with the default setting of 72 ppi, you can still correct the file. Since these are live effects, changing the resolution will force Illustrator to redraw all raster effects in the document (note the word "Document" in the command) on the fly at the higher resolution.
For some users this is a good workflow … 72 ppi raster effects keep the file size relatively small so the response time is quicker. They save the "change to 300 ppi" step for last. These users also ride motorcycles without helmets while picking up Mother's Day carnations from the 7-11 on their way to Mom's special brunch.
When it's Too Late
A lot of Illustrator users are not clear on the difference between the Effects and the Filters menus, which share many of the same commands. Effects are "live" and can be edited on the fly (including changing their resolution); Filters are permanent changes to the artwork and can only be changed by Undoing, if you're lucky.
Most of the time, when you're using filters, you're going to be aware of the resolution Illustrator is using because most of the filters only work on raster images. If you really want to use that filter, you'll have to convert the selected vector artwork to a raster first, via Object > Rasterize, and doing so forces you to set the resolution in the Rasterize dialog box. No surprises, then.
But there's one filter which, while it generates a raster, doesn't require you to rasterize the vector artwork first. This is Filter > Stylize > Drop Shadow. So how does it know what resolution to use for the shadow? Why, whatever you've set in the menu next door, the Effect menu, son! Makes perfect sense!
Changing the resolution in Effects > Document Raster Effects Settings will not redraw the shadow you created with the Filter command, since filters are a permanent change. If you accidentally created a blocky 72 ppi shadow, you're not the first to so. Luckily, the default setting for the Filter drop shadow is to "Create Separate Shadows", meaning the shadow is on its own layer. You can find that in your Layers palette, delete it, and then re-apply the drop shadow filter after you've increased the resolution in the Document Raster Effects Settings dialog box.
Or, just ignore the Filter for drop shadows from now on. Stick to its twin in the Effects > Stylize submenu and you'll never have to worry about making a permanent boo-boo again.
Fix the Default Setting
If most of your Illustrator work is for print, and your computer has a decent speed and amount of RAM, why not just change the default setting for Document Raster Effects from 72 ppi to 300 ppi?
As with most of Illustrator's application defaults, you do so by changing the hidden template Illustrator uses for new documents. There's two of them, one for RGB docs and one for CMYK docs. They're in the Illustrator application folder, so you'll probably need to have an admin account (not a restricted user account) on your Mac or PC to get in there and edit these 2 files.
You find "Adobe Illustrator Startup_CMYK.ai" and "Adobe Illustrator Startup_RGB.ai." in the Adobe Illustrator > Plug-ins folder. Double-click them to open them up in Illustrator, then for each one, go to Effects > Document Raster Effects Settings and change the resolution to 300 ppi (or whatever default resolution you prefer). Click the Okay button and close the document, saving your changes.
>From now on, any new document you create in Illustrator will use your setting as the default resolution for raster effects from the Effects menu, and for that Filter > Stylize > Drop Shadow land mine too.