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
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 as you can see in the samples below.
RGB to CMYK Color Variances
However you supply files to be printed, the colors should be designed or converted to CMYK. This can be done through a photo editing program such as Adobe Photoshop, layout programs such as Quark Xpress or Adobe InDesign or when converting to Adobe Acrobat PDF format using the Press Quality settings. You’ll find more information on creating PDFs below.
For more information on CMYK printing check out http://en.wikipedia.org/wiki/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.
There are many pixel based art file types. Some examples are:
- .tif (tagged image file) – a pixel based format with a preview (tag) embedded. A standard print file format.
- .jpeg (joint photographic experts group) – a pixel based format with robust compression options. JPEGs are often used for web images but are entirely appropriate for printing if high resolution, not compressed too much and CMYK.
- Photoshop EPS – (encapsulated post script) not to be confused with Illustrator EPS, a vector art format. Photoshop EPS is like .tif in that it carries a preview (the encapsulated part) with the file.
- .gif – (graphics interchange format) – almost always used for web images and rarely appropriate for printing.
- .png – (portable network graphics) – 1st cousin to the.gif and also used mostly for web graphics.
The other digital art format that is used for printing is called a vector art file. Vector art formats use algorithms to describe the image giving it three major advantages for printing.
- Vector art is effectively infinitely high resolution. Since the image is calculated at the press the only limitation is the presses RIP (Raster Image Processor).
- Since vector art resolution is determined when processed it can be scaled up or down with no loss.
- Since vector art is code based in concept it is very economical and can be very small in file size.
Vector art is used where line art or graphics are appropriate and is often used to set type since it describes type as lines rather than pixels.
For more information on image resolution:
For more information on graphic file formats:
Download the Influence Graphics Printing Guide which contains a complete listing of printing terms and definitions.