Illustrator does not size items by pixels. Yes, I know there is an option for “pixels”, but since Illustrator works on a physically sized canvas (inches, picas, centimetres, etc.), there must be a conversion to say how many pixels per inch the artwork is. There is not, or rather, there is only one value, 72 pixels per inch. This is the same as sing “points”.
If Illustrator’s pixel unit were actually to mean a pixel, then imported raster art would come in at one pixel per pixel, meaning your 100 x 66 pixel image would import at 100 x 66 pixels. But that image also has a resolution, in pixels per inch. This is just a conversion factor built into the image to tell other programs how to convert the pixels in the image to a size on a page. That value is 300 pixels per inch. Illustrator is scaling your artwork so that 100 pixels is reduced to one third of an inch (one third of 100 pixels at 300 pixels per inch). One inch is 72 points, so one third of an inch is 24 points.
You can open the image in Photoshop or another raster editing application and change the resolution to 72 ppi (with resample OFF) or scale it up in Illustrator to 100 points.
This annoyance is not your fault, it is Adobe’s for using the measurement “pixel” wrongly in a vector drawing program. I do not know how Adobe, the makers of Photoshop, could screw this up so badly for so long and never bother to fix it, but that’s how they do things over there.
This annoyance is not your fault, it is Adobe’s for using the measurement “pixel” wrongly in a vector drawing program. I do not know how Adobe, the makers of Photoshop, could screw this up so badly for so long...
I sort of understand what Scott is getting at, but I'm inclined to cut Adobe a bit more slack here.
The pixel as a unit of measure was added to Illustrator concurrently with the addition of the RGB document mode -- circa version 9. Don't believe me? Just fire up AI 8. The program doesn't understand pixels -- not in prefs, not in the rulers, not in any of the dimension fields.
Clearly, with more people using Illustrator to create artwork for Web sites or, more generally, for monitor viewing, it was necessary to enable working in RGB spaces and dimensioning in pixels (referenced to 72 ppi).
For print work, Illustrator is the same as it has always been. If you work in CMYK, use absolute units of measure (and, no, a pixel is not an absolute unit of measure -- no more than an en or em space is an absolute unit of measure -- we've had discussions about that here), and keep raster element resolution in the range of 200-300 ppi, then you'll be in good shape.
And, I'm sorry, but if you thought pixels were an actual unit of linear measure, then these kinds of mistakes are your fault.
Thanks Scott; as I only create print materials for my web design company, I tend to forget these things... My confusion arose from the fact that on mouseover in the open file dialogue, the resolution was listed at 100 x 66, whereas when the file was a mere fraction of that in the property inspector... Thought I might be losing my mind...