Pixels per Inch and Dots per Inch

Every time we turn around today, when it comes to image resolution, it's pixel this or pixel that. Computers, cameras and websites talk in pixels per inch (ppi). Printers, on the other hand, want you to forget those silly pixels and talk to them about dots per inch (dpi). As dissimilar as apples and apricots, ppi and dpi  refer to two totally different concepts. Printers' resolution numbers have nothing to do with either the size or number of pixels in your image. 

On the web you'll find many excellent, esoteric explanations of pixels, dots and resolution. On this page we'll simplify the matter and give you only as much information as you need to know.  

Most printing for short runs is done on presses that do not use traditional printer's inks; instead, they use toner (similar to what's in a laser printer), which is fused to the paper either by an electrostatic process or through spray nozzles laying down a certain amount of toner, based upon the dots per inch. It's Back Channel Press's responsibility to find a printer with the appropriate press to fit the type of printing your book requires. It's your responsibility to provide us with images that can be adjusted to meet printers' requirements. 

Pixels
All digital images are made up of tiny squares called pixels. What you see on a computer monitor is referred to as pixels per inch. On the sidebar, you can see a sample of a small area of a picture blown up to show each pixel. 

Dots
All printed images are made up of tiny dots called (thank goodness) dots. Printers require 300dpi for quality image reproduction.  

Digital Camera Images
The resolution of any photo taken by a digital camera is 72ppi or 180ppi for the newer cameras. To convert a 72dpi/180ppi digital image for printing at 300dpi, your pictures need to be as large as possible, taken at a setting most digital cameras call ‘fine mode.' The picture can then be reduced and those pixels squeezed into a smaller area. This results in more pixels per inch, which can then be successfully converted to 300dpi. 

Website Images
These images are usually at 72ppi, but the images themselves, unlike those taken by a camera, are much, much smaller. To try to beef them up with enough ppi for printing at 300dpi requires adding pixels. Computer programs do this, but unfortunately, rarely with satisfactory results - the images come out decidedly fuzzy. Lifting images from websites is not recommended.

Scanning Images
All images should be scanned at 300dpi and saved in formats know as either ‘jpeg' or ‘tiff.' Tiff files are much larger but are preferred, as they are more stable. Each time you work with a jpeg file it will depreciate a little. 

Image Review
Back Channel Press will open each image in Photoshop to verify and/or change its size and resolution. We check all the color values to make sure they fall within a certain range. We then apply whatever various computer adjustments are necessary to truly bring your image to life.