Large Format Printing Guide – File Formats

First, what is large format printing? Large format printing is often referred to as poster or sign printing on paper or banner material. Large format printing refers to digitally printing pieces that are typically large (bigger than 12″ x 18″) and not economically produced on an offset press due to size and quantity. We are often asked what is the best way to setup a file for large format poster output at CQ Printing. So we will be creating several blogs to help guide you with the basic fundamentals in setting up your electronic files for large format output. We will discuss file formats, file resolutions and ideal file setup for your particular needs. This particular blog covers file formats, and common terms used in large format printing.

Basically there are three types of electronic files. The first is a vector file, the second is a raster file and the third and most common is a combination of both vector and raster together in a single document.

Vector based files are typically illustrations or clip art items containing fonts and objects created with the pen tools, where points are created and connected together with either straight lines or arcs made using mathematical calculations and saved in a postscript language. One of the reasons vector art is ideal for large format is because it is mathematically based, which keeps the file size down and allows the file to be scaled up to any size without losing quality. The most common vector based programs are Adobe Illustrator, Freehand and Corel Draw, although most page layout programs also offer vector tools of some kind. Vector files are most often saved as an EPS (or Encapsulated PostScript) file.

The second type of file, the raster file, consists of tiny color squares called pixels. These pixels combine to make photo images. The most common raster based program is Adobe Photoshop, although all digital cameras and scanners also save their files automatically as raster files. Because each pixel contains a unique color, the more pixels originally captured per inch in your file, the better the quality, and the less you notice the tiny square pixels. When the square pixels are large and noticeable in your image, that is called pixelation and is caused from not having enough square pixels per inch. Pixels or dots as they are referred to commonly, are designated in either PPI (Pixels Per Inch) or DPI (Dots Per Inch). The amount of pixels contained in an inch is referred to as the resolution of the image. When your file shows pixelation, it is said to be of a low resolution. Images where the pixels are not noticeable in the final product are considered high resolution. Raster files can become quite large in the size or space it takes up on a computer disk. We will discuss correct resolutions later in this blog which varies for the size of the final output desired in your large format posters. Raster files are typically saved as .tiff, .psd (photoshop), or .jpg files.

The third and final file format type is the most common. It is the combination of both vector and raster images contained in the same file. Most large format prints contain multiple items including fonts, graphics and photos. Also, if you apply any effects used in your vector programs like Adobe Illustrator, those effects are raster based and have transparency – this greatly adds to file size and you must have correct settings in your “Document Raster Effects Settings” to ensure best output for these effects. Most combo files are created using a page layout program such as Adobe Indesign, QuarkXpress and can also be created using any of the above vector based programs like Illustrator. Common file types include native files such as .indd, .qxp.  or .eps files, and the very common .PDF (portable document file).

Now that you know the 3 basic file formats, vector, raster and a combination of the two, we can discuss some aspects that are included in each of the program formats. The first aspect is color. There are several color modes which can be used inside each file type, but there is only one you should be working with when it only involves our large format printing. Our printers use CMYK inks (Cyan, Magenta, Yellow and Black), these are also referred to as 4-color process inks. So obviously, the color mode that should be used in your files is CMYK. If other color modes such as RGB, LAB, or Spot Color Swatches are used, the output may not match your file as close as you may like. Our printer and programs will do their best to match your files as close as possible in CMYK mode, but exact matches are not always possible due to the differences in color range or gamuts between the different color models. Also remember that monitors use RGB color modes, so unless you are working on a monitor that has been calibrated to match CMYK, printed output will not match your screen, and is commonly less vibrant due to the smaller color gamut.

The final topic we will cover in this blog are things you should do in your files to help ensure the least amount of problems. First, use the correct color mode, CMYK. Second, make sure if you have raster images that they are high enough in resolution to produce good quality output. Our next blog will discuss how to decide on the best resolution, but as a simple guideline your image’s resolution should be no lower than 72 dpi (or ppi) at the file’s final output size. Thirdly, remember to send along all files that are used in your native document. This includes fonts, photos, placed graphics or any other linked items. One way to ensure that these items are included is to outline your fonts (also referred to as turning them into paths) and embed or rasterize your graphics into your file. This can also be achieved by creating high-resolution press quality PDF files, that have all these items embedded. Finally, remember to include bleed on your file if the image goes to the edge of the print. Bleed is the extra image that extends at least 1/8th of an inch past all 4 edges of the page onto the program’s pasteboard. In Photoshop you will need to increase your canvas size at least 1/4 inch to achieve the 1/8 of an inch all the way around your image. In PDF’s remember to change your settings to include both your 1/8″ bleed and crop marks to help us know where to trim your file, as we cannot add these extra items to your file once the PDF has been created from the native program.

This concludes the first blog on large format guidelines. We hope this is helpful for those that have not ordered large format poster prints before. Our next couple blogs on large format go a little more in depth into file resolutions and image sizes. We will also be adding a blog on large format media and finishing, which will include the best type of printing media or paper for your project, and different post print finishing options such as mounting and laminating of your prints. So keep checking back periodically on our blog page for more about CQ Printing and the services we offer.