We hear this question often and would like to give a series of in-depth answers.

Creating a press-ready file requires some understanding of a few basic elements that make up a huge part of our every day life here in the offset printing industry. Those elements are: 

1. resolution

2. color mode

3. document size (bleed size vs. trim size)

4. file type

For now we will keep things simple and describe full color process printing (also known as CMYK printing or four color process) since that is what we do a majority of every day. In a future article we will get into 1 color, 2 color and 3 color printing. 

To keep this post short we will cover the first element: resolution. Following posts will cover color mode, document size and file types in-depth. Hopefully these posts will answer most of your file submission questions.

Resolution:

In full color printing the colors Cyan, Magenta, Yellow and Black combine in a series of tiny dots that make up halftone screens. To keep it short and simple, the pixels (or rasters) that make up the images in your design layout are translated into dot patterns (halftone screens) made up of any or all of the CMYK colors. The dots are separated by color and translated to metal plates which are then mounted onto a press. The metal plates are inked and each plate transfers one of the four ink colors onto a blanket which then coats the paper with ink. Therefore, your images need to be at a certain resolution from the beginning in order for a commercial offset printing press to print them at the highest quality possible.

So, what is the correct resolution for printing? Raster graphics such as TIF and JPEG files must have a minimum resolution of 300 dpi (dots per inch) in most cases. Images with a resolution less than 300 dpi will reproduce poorly on press and result in an image that looks fuzzy and/or pixilated). To determine the resolution that is suitable for printing a simple math problem is involved:

line screen x 2 = image resolution

Ok, so what is line screen? We won’t go into too much detail regarding line screen. To sum it up, line screen is the resolution of the halftone screen. Offset presses usually print at a line screen no less than 150. At Tornado Printing, we print at 200 line screen. So, for an even sharper printed image you may submit your files at 400 dpi. If you contact the pre-press department at any offset print house and inquire about the required image resolution they will usually refer to the required dpi and skip the info about line screen. It is always good to know why you follow the rules that you do, so we figured we would clue you in on line screen.

Now, are your images at the correct resolution for printing? Remember 300 dpi is the minimum resolution in most cases. If you took your images from a website, there is a good chance that they will not  be at a high enough resolution for printing (unless the images came from a stock photography source and are designated as high resolution). The internet displays images at 72 dpi which is only a quarter of the resolution that you need. These images should not be used for commercial offset printing. They are not large enough to reproduce properly. As a general rule of thumb Large images can be scaled down but small images should never be scaled up in size. If an image starts out small there is no way to increase its number of pixels with out degrading the image.

In the high line screen gang run printing world JPEG and TIF files have become the common file-of-choice for most designers since they essentially are just images. There is no chance that a font will change or an image not appear in the finished printed piece. It is the what-you-see-is-what-you-get approach. But to get a nice finished piece you must start at the proper resolution (300 dpi minimum.) The other factor that plays in from the beginning is document size, bleed size and trim size to be specific, which we will cover in-dept in our next post.

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