It is preferable to receive vector images such as Adobe Illustrator (.ai), Corel Draw (.cdr), and Illustrator (.eps) files.
Vector art consists of creating paths and points in a program such as Illustrator or Corel Draw. Vector artwork is scalable, keeping its proportions and quality when sized up or down. This type of artwork is created in Illustrator, Freehand, Corel Draw, Flash or other vector illustration programs.
Vector-based images are mainly used for spot-color separations such as typefaces, solid-colored graphics and clip-art images.
Raster art consists of individual pixel information, where every pixel is assigned an RGB or CMYK value. This can create smoother and more detailed images for photos and paintings. If the image is scaled, the program has to create new information resulting in the distorted look shown above. Raster programs include Photoshop, Fireworks and MS Paint.
Raster-based images are designed for high-end, photorealistic work. These images are used for process color printing. Unlike vector images, the quality of a raster image is directly related to the image's resolution or number of pixels. Vector images, on the other hand, are created by mathematical equations, so pixels don't impact the quality of the image. As a result, they can be scaled up or down in size without loss of quality. Best results are obtained from images that are high-resolution (300 dpi or greater). Images taken from web sites are not high-resolution (generally 72 dpi) and cannot be reproduced well on a T-shirt.
Types of printing. Which one is right for you?
Spot color printing (see example)
Single seperated colors applied to printing:
Process color printing (see example)
The four basic colors of ink used in process color printing are cyan, magenta, yellow and black. These inks are transparent and produce different colors when overprinted in predetermined amounts. For example, when cyan overprints yellow, it produces green, and when yellow overprints magenta, it produces orange. Different combinations of the four basic colors can produce a full spectrum on a printing press.
Simulated Process printing (see example)
Simulated Process is another advanced technique that uses halftones of a few ink colors to represent the colors in the original design. This process differs from 4-color process in that the inks are solid opaque colors usually printed on dark colored shirts. Since the shirts colors are normally dark, simulated process requires the use of an underbase. Depending upon the design, up to 11 ink colors may be needed to accurately reproduce the various colors.