What You Need to Know!
So you’re ready to print your special piece but don’t know exactly how it all gets done! Not to worry, there’s lots of printing tips here to get your files ready to go to the press. From the basics to the specifics, the key to any successful print run is careful planning. However, it’s tough to plan when the basics seem cryptic so let’s start with some key concepts.
Computers, Printers and Color Models
In our modern world of computer desktop publishing there are two basic ways that color is described – RGB (emanated light) and CMYK (reflected light).
Your computer monitor emits light based on the RGB model making the various colors by the combination of Red, Green or Blue light coming from your screen. Since the addition of intensity to these colors produces white it is also called an “additive” color model.
In contrast, a printed piece gets its color by the light reflected from it which comes from the inks used and the ambient light. Most printers use an ink scheme called CMYK, which stands for Cyan, Magenta, Yellow and Key (Black is almost always the key color. Just think of the “k” at the end of black and you’ll remember CMYK). Since the subtraction of these colors produces “white” (or whatever the color of the paper underneath) it is also called a “subtractive” color model.
The important thing to understand is that RGB color is very different than CMYK color and you need to make sure that the images and colors used for print are correct. Most important is that not all RGB colors will print CMYK as you see them on your computer monitor. Bright blues, bright greens and pinks are notoriously difficult to convert from RGB to CMYK.
Resolution and Printing Tips
Image resolution is an idea that was born with desktop publishing. Prior to digital printing an image might be called “soft” or out of focus but the blurriness was a result of the photographic process. When it became possible to digitize images the issue of resolution became very important because printing required high resolution but it also made image files very large and difficult to work with. In trying to cope with those problems image programmers have come up with two basic solutions.
Pixel art or “bitmap” is a digital image format that literally defines how many pixels are present and what color value each pixel has. For a brief overview of color models you can see the previous section but the big issue here is How Many Pixels Per Inch? or in a word – resolution.
Resolution is a factor of width and height and you can figure pixel resolution by multiplying the number of pixels in each for the total number of pixels – just like figuring area. The problem is that a pixel is an abstract idea and even though you can have a lot of pixels they need to ultimately translate to print units which are called dots. So for printing, resolution is described as dots per inch or dpi. Basically, however many pixels are in an image at the target resolution will give you the real printing resolution. For example, if you have an image that is 300 pixels x 300 pixels and you want to print at 300 dpi, you will have enough pixels to print an image 1 inch x 1 inch.
300 dpi is the recommended resolution for digital printing.
To understand a practical application – if you have an image that you want to print 5″ x 7″ at 300 dpi you will need an image resolution of 1500 pixels x 2100 pixels. This results in a rather large file size of 12 MB if the image is CMYK.
You can’t add resolution if it isn’t there to begin with. If your source image is 72 dpi, as many web images are, you can change its pixel depth but it won’t help its apparent resolution. If it started out at low resolution adding pixels just adds file size but can’t make up for its lack of definition. Web images will almost never have enough resolution to print well. Most current digital cameras (4 megapixels and up) have good enough resolution to print 8.5 x 11 at photo quality.