Printing digital images three or more feet wide on high-resolution printers requires starting with extremely large photos and/or careful post production to prevent magnification of undesirable artifacts. The goal is for tonal qualities to blend smoothly. In the digital world, what we think of as continuous tones is actually a grid of tiny squares. Their imperceptible at small sizes but when enlarged a several hundred percent, the underlying smooth facade is revealed.
Professional photographers generally use DSLR cameras with extra large sensors (sometimes four times the size of consumer cameras) capable of recording significant detail even in low light settings. The ability to save uncompressed digital RAW photos with pro cameras or 16-bit images is also conducive to enlargements.
Regardless of hardware, sufficient pixels are necessary. Consumer cameras like the Canon PowerShot SD790 support 10 megapixels. Just purchasing such a camera, however, still does not guarantee optimum results. Most cameras do not come with the largest file size enabled by default. Consumers are often more impressed by how many images they can store. Even with the highest setting, it is often a mistake to enlarge one face in a group shot into a large portrait. If a portrait is desired, walk up close to the subject so all those megapixels are not wasted on the background.
Controlling ambient light is another challenge for budding photographers. Insufficient lighting reduces contrast and can blur focus, significantly degrading quality of enlarged images.
Graphic designers form an increasing reliance on the seemingly limitless supply of images from digital stock photo libraries. Many have popped up allowing photographers of varying proficiency to upload their work. One potential problem is what may be sold as a high resolution image may simply be an enlargement of a lower resolution photo. Improper JPEG compression often introduces artifacts. It has also been observed that, perhaps to draw more attention to their images, some photos include colors that fall far beyond the gamut of printers. Disappointing color shifts and banding within gradations can occur.
Let's sum up options for best results.
- hire a professional photographer with proper equipment
- purchase one of the new high megapixel cameras
- modify pixels so they are not annoyance when enlarged