Resolution and color depth

The simplest way to understand resolution is that, in the world of printed images, it is a measure of the sharpness of an image. (It's easy to confuse this with the word "resolution" as used in the world of computer displays, where it's a measure of the size of an image.)

Resolution and scanning

The scanning resolution, simulated here, affects how sharply the image will resolve, at a given size. All other things being equal, the lower your scanning resolution, the fuzzier your images will be when you enlarge them.

When it comes to scanning, the issue that comes up most critically is what resolution setting to use when scanning. These settings are usually expressed as a certain number of dpi, or dots per inch. (This term is borrowed from printing, and is not precisely accurate for scanning, but it's commonly used by scanning equipment manufacturers, so we use it to help you compare doing scanning yourself with using our services.)

Our philosophy on resolution

Scanning service providers differ on what resolution settings to offer. In our experience, the right choice is a resolution that is high enough to allow a range of enlargements, but with a manageable file size.

Why high resolution? Because if you're going to go to the trouble of scanning a number of old images, you might as well do it in a way that gives you (and your family) options down the road — to print photo books, merchandise, and enlargements, and possibly even display on HDTVs. It's hard to predict the future — why risk having to scan your images all over again?

Why not the maximum resolution possible? The higher the resolution, the more detail in the scan — some of that detail is a good thing, but some of it — scratches and grain, for example — are not, and that makes extremely high resolutions attractive to professionals only. Also, higher resolution creates larger file sizes, which can cause trouble for consumers who have thousands of images. This is less of an issue for professionals, who have long been accustomed to having terabytes of storage for their photos.

So in our philosophy, a 600 dpi scan for photos and a 3000 dpi scan for slides and negatives is the golden mean.

ScanCafe and competitors

Resolution is just the starting point for a top-quality scan, but we believe so strongly in scanning with appropriate spatial resolution that we don't even offer a low-resolution option, as most of our competitors do.

Minimum Resolutions & Equivalent Megapixels — ScanCafe vs. Competitors

Format	Competitors	ScanCafe
Photos (5" x 7" prints, for example)	300 dpi (3.0 Megapixels)	600 dpi (12.5 Megapixels)
Negatives (35mm)	2000 dpi (4.5 Megapixels)	3000 dpi (10.5 Megapixels)
Slides (35mm)	2000 dpi (4.5 Megapixels)	3000 dpi (10.5 Megapixels)
source: ScanCafe, competitor websites (January 2009)

Color depth

One last related issue is color depth, which measures, in effect, how many distinct colors are possible in a scanned image. Scanners do this by assigning a certain amount of space in their computer memory for each type, or "channel" of colors (red, green, and blue, almost always). As with resolution, there are tradeoffs here as well, and our philosophy is to scan at what's called True Color, which is 8 bits of memory per channel. Since there are three channels, this is also referred to as "24-bit" color.

As the total bits devoted to displaying colors increases, the number of distinct reproducible colors increases. Beyond 24 bits, however, the potential improvements are relatively small.