Crop marks are those things that you don’t realize you need until it’s too late usually. If you send a job off to the printers, or trim a printed piece, you will quickly realize what I’m talking about.
Crop Marks come from the commercial printing world (but read on, everyone can use them).
When you send your work off to a printing press, they are going to trim the final piece, even if it’s a standard size. The reason for this, printers use larger sheets of paper, or even huge rolls to print from. On an offset (big rolls) or sheetfed printer, the final is going to be trimmed. If you have designed all the way to the edge, there is a possibility that some of your work will be cut off, or some white edges will be showing. Neither of these are a good thing.
To combat that, there is usually a safe region where the design “bleeds” over. You usually create a 1/8″ border all the way around and let your design fill the larger size. Keep all your elements within the bleed area so it will look nice and clean when trimmed. Because there is a 1/8 border, the trim will look really nice even if the paper slips a little bit. This is where crop marks come in. Crop marks show the printer where to trim the final piece. Photoshop doesn’t have the ability to create crop marks by default. This quick video will show you how to make your own crop marks in Photoshop.
Please note, that it’s preferable to create the bleed area and crop marks BEFORE you begin your design. However, this video shows you a work-around if you have already created your design.
See this great article from Gregg on preparing files for going to a commercial printer.
Also bear in mind, if you are printing at home on your inkjet printer and need to make a little trim, you can also use crop marks.
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