How to meet dots per inch requirements for images
Neil Blair Christensen, Hiroyoshi Suzuki, Yuko Fukuda · International Journal of Urology · 2009
Authors are often challenged by DPI (dots per inch) requirements. Here, we provide a brief explanation of DPI. To understand DPI in electronic images, we must understand pixels, because electronic images consist of pixels. Pixels are the smallest elements that sometimes appear as little squares in zoom view. Think of pixels per inch (PPI) as equal to dots per inch (DPI). Technically speaking, DPI and PPI are often confused because they can mean different things. For instance, a 1200 DPI printer can print a digital image at 300 DPI (PPI) using 1200 ink dots per inch to render 300 pixels per inch, e.g. 4 ink dots per pixel for high detail. Forget about this. The DPI requirements in journals are not about DPI capabilities of printers, but about DPI as equal to PPI (dots = pixels). Think of DPI as a spatial measurement for printing dimensions. When the width of an image is enlarged for publication, the DPI of the image decreases because the amount of dots within an inch decreases. Compare it to looking through a fixed scope at a dotted balloon being inflated. DPI requirements ensure that electronic images have enough pixels (dots) to print at required dimensions (inches). These dimensions are typically single column width, 1.5 column's width, or full page width, which translates into various amounts of inches (Table 1). As an example, an image meant to publish at 10 inches width and 100 DPI is 1000 pixels wide (10 inches × 100 DPI = 1000 pixels). An image meant to publish at 3.333 inches (82 mm single column width) and 300 DPI is roughly 1000 pixels wide (3.333 inches × 300 DPI = 1000 pixels). DPI decreases proportionally to increasing dimensions. To make sure images look good, view images in their normal size on the PC screen. Most imaging software provides this, as well as functions to count the amount of pixels. Image files often state a DPI in their properties, which can be ignored as far as the software does not know what dimension the image will publish at. However, printing companies may look at this DPI number as an instruction for the intended size/width, and ask for a new image if the stated DPI is too low. These DPI numbers can be changed in imaging software as needed, but to make a long story short, avoid re-sampling images when changing the DPI value, because that means changing the amount of pixels, and hence the basis of your calculation. (Inches × DPI = pixels) OR (Pixels/inches = DPI) Look up required image dimension (width) in the author guide, or measure it from a printed copy of the journal. Determine the likely publication width of the image. If in doubt, submit an image with a larger than required width. Look up the required DPI in the author guide for the image type (color, b/w, line art etc.) Determine the amount of pixels-width of the image (right-hand click image icon; select properties/summary/advanced; or look in attributes in the imaging software). Ensure that there are enough pixels for the required DPI (Inches required × DPI required = pixels required). View the image in its normal (full) size on the PC screen to make sure it looks good. Wiley-Blackwell artwork guide. Available from URL: http://authorservices.wiley.com/bauthor/illustration.asp Elsevier artwork guide. Available from URL: http://www.elsevier.com/framework_authors/Artwork/Complete_AAI-2009.pdf Springer artwork guide. Available from URL: http://www.springer.com/authors/manuscript+guidelines?SGWID=0-40162-12-331200-0 Weistra R. Misunderstandings about DPI.[Cited 24 May 2009.] Available from URL: http://www.dpiphoto.eu/dpi.htm