File Format

Why Does Reprographics Accept Only PDF Files?

PDF is a file format that means "Portable Document Format."  It provides an electronic image of text and graphics the way it will look when printed. PDF files can be viewed on the computer, printed, and be electronically transmitted.

1. Accuracy
   Unlike other file formats, PDF files are displayed the same way no matter what computer system is displaying it. This ensures that what we print on paper will look like what you have on your computer screen. With other file formats (such as MS Word, Powerpoint, Excel, and Publisher) the file’s appearance will vary depending on what system is running the program. We have had problems with margins changing, fonts disappearing, words being cropped off, paragraph spacing being altered, and other uncontrollable layout changes occur without warning. Because of these frequent, unpredictable changes, we will not print MS Office documents.
   
   
2. Quality
   Another advantage to PDF files is that text is often saved as vector data instead of pixel data, which means that the text in the file can be scaled to any size without losing quality. For more information about image quality, please reference the following page.
   Formats such as JPEG and GIF were designed for displaying images on a computer monitor but not for printing. JPEG files compress an image so the file size is smaller—this makes it faster to download; however, the price is quality loss. Details become blurred, object edges become simplified (aliasing), and strange blobs and blurriness appears (artifacting). GIF files make file sizes smaller by reducing the number of colors used and it compresses the data, which can make it look grainy. To ensure the quality of what is being printed, we do not print these file formats. The Chabot logo on the left is a JPEG and the logo on the right is a PDF.
      
   
   
3. Compatibility
   The final reason that we need PDF only is that our print queue software reads PDF only and can not process any other file format. In other words, if you send us a MS Word file, our print queue can’t read it.

Vector versus Raster and Dots Per Inch (DPI)

There are two ways to save image data: vector and raster/pixel.

Raster images are like a mosaic: created by colored tiles on a grid. These colored “tiles” are a picture element (a pixel). A raster file saves what color each pixel in the image is (for example: A1 is blue, A2 is blue, B1 is yellow, B2 is yellow). When you make the image bigger, the pixel squares get bigger. By making the pixels bigger, you can see the individual pixels easier, which makes the image look “pixelated,” which means edges look jagged and diagonal lines look like a stair case. In order to remove those jagged edges, the edges can be rounded, but that will make the image blurry and cause artifacting.

Pixels are dots that make the image and these dots can be different sizes, the term “dots per inch” (DPI) tells us how big these dots are. A computer screen needs only 72 dots to display a 1 inch by 1 inch image (72 dpi). A printer needs 300 dots for a 1 inch by 1 inch image (300 dpi). As a result, an image needs to be three times bigger on your computer monitor than what you want it to be when printed (if you want a picture to be 5” in size on a piece of paper, it needs to be 15” in size on your computer monitor).

Most images found online are low-resolution 72 DPI raster images and are not suitable for printing. Printing them results with a low-quality image which looks unprofessional and reflects poorly on the institution. Additionally, most images online are copyrighted and using them might violate copyright law.

To ensure the best quality: files submitted to be printed should be formatted to the size you want it to be printed at 300 dpi.  For example, if you want something to be printed at 11 x 17”, you should give us a 300 dpi file that is already 11 x 17”. While 300 dpi is preferred, 200 dpi can work in many situations and is the lowest resolution that should be printed.