One drawback to the S1iS is its "low" resolution of 3.2 megapixels.
(Strictly speaking, the camera is 3.1 megapixels: the largest images it takes are 2,048 x 1,536 = 3,145,728 -- which rounds out to 3.1 million pixels.)
At the photo counter, the salesman/woman will solemly intone that this is good enough for only 4x5 prints. How come? Hard to say. There are some rules-of-thumb that relate number of pixels to the largest print size -- some people say 200dpi (dots or pixels per inch); Picasa warns you when the dpi falls below 128.
Let's take the value of 128, and divide it into the largest images the S1iS takes:
2,048 / 128 = 16"
1,526 / 128 = 12"
Well, that's not bad: you can make prints as large as 12" x 16" -- assuming, of course, that your printer can handle sheets that large.
(Technically, you need a B- or C-size printer, which handles 11x17" and 17"x22" paper sizes, respectively. These printers are bigger, and much more expensive, than the $99 A-size printers most people own. And, by printing large areas, they use up ink much faster.)
Bumping the Resolution to 8 Megapixels
There is a workaround in the S1iS (and other cameras) that lets you take very high-resolution photographs. It's the Photostitch feature. Read about it the manual that came with your camera.
Photo-stitching lets you take four pictures of a scene. Later, on your computer, you use the PhotoStitch software (included on the Canon CD-ROM) to stitch together the four into a single, high resolution photo.
The image above shows four photographs I took of the Fraser River (British Columbia, Canada) from the bridge at Hell's Gate. (Click the photo to see it larger.) The green rectangles are the overlapping areas of the four photos. The edges are curved, because the PhotoStitch software warps the photos to adjust for the changed point-of-view.
When cropped (to remove the irregular edges), the stitched photograph has a resolution of 3696x2283 -- which works out to about 8.5 megapixels. Using the 128 pixels-per-printed-inch rule, I could print this photo 2.5-feet wide by 1.5 feet tall. (Click the image at left to see larger image of resolution- and color-reduced photo.)
PhotoStitching is not limited to 2x2 photos. You can also take strips of photos: up to 26 photos wide or tall. Sometimes it works; sometimes it doesn't. The most spectacular stitch photo I've taken is of the Skycity tower Auckland (New Zealand) -- from its tip down to the front entrance of our hotel, some blocks away. It helped that I was 130 feet in the air (ie, on the 13th floor of the hotel). That stitch photo consists of 14 photographs; the resolution is 15 megapixels.
Stitch photos are good for:
* Obtaining wide angle views.
* Quadrupling the resolution.
Stitch photos don't work when:
* The subject matter is ineffective.
* The camera plane is not perfectly horizontal or vertical.
* The lighting conditions change (the S1iS uses the same exposure for all photos in the stitch series).
* People and other objects are moving in the scene (they look wierd at the seam overlaps).