The Great Bugaboo: File Resolution

Often people have the mistaken belief that images that look great on their web site should also work well when they grab them from their site and provide them to printing service providers. Web images display very well at 72 pixels per inch (often referred to as ppi) on a computer screen but printed images on paper or other substrates work best at 240 ppi and above for various forms of inkjet printers, and 300 ppi and above for offset printing purposes. (There is a little bit of wiggle room in these suggested image resolutions, however scaling an image with correct resolution upwards beyond an approximate 10 per cent variation may potentially lead to creating degraded final output). This resolution issue is heightened when the images need to be printed larger than they appear on the web site (which is often the case as web images are usually small in width times height appearance, as well as consisting of low resolution within the file) because enlarging images doesn't increase the ppi, as one might think. Instead, enlarging the image just causes the pixels to get bigger as you spread them out, leading to that "blocky" appearance often seen in images. This blocky appearance is often described with one of a number of different names or descriptive phrases, such as having "the jaggies" or being "bitmapped" or being "stair stepped" or containing "aliasing", or even just “yuck!”. (Anti-aliasing is the process of blurring edge pixels using image transparency techniques to minimize the rough effect, although this procedure does not add pixels nor alter image resolution, which are the optimal ways to correct low resolution images.) You can save time in the production process and ultimately achieve much better printed results if you can locate and provide the original color corrected photo to your graphic artist, rather than by "grabbing" the image off of your web site. Look for my forthcoming related blog post Bugaboo Number Two: DPI versus PPI.



Carl G.

Friendly, Patient and Expert Mac and Adobe Software Tutor

300+ hours
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