DPI, PPI, and Resolution in Digital Scrapbooking

Welcome to our overview of what is meant by resolution in digital scrapbooking. We hope that we will be able to shed some light on some terms and clear up some misconceptions. Let's start off with some definitions.

Two terms you will hear in the digital scrapbooking world are dpi and ppi. Often they are used interchangeably, even though they are two totally different things. DPI is "dots per inch" and is used for print material. PPI is "pixels per inch" and refers to how images are displayed on computer monitors. Quality printing on an inkjet is typically in the range of 150dpi. The relationship of ppi to dpi is about 2:1 - that is to get 150dpi for quality printing, you would send the printer a 300ppi image (300ppi divided by 2 equals 150dpi). If we want to know how many pixels we need to print a certain size, we can multiply our ppi by the number of inches. For example, to print a 12" x 12" image, at 300ppi, we would need 3600 pixels by 3600 pixels.

You will hear it said that you must only use 300ppi for quality images. That's not true. In fact, many digital cameras use 72ppi, as do many stock photo houses. It's the number of total pixels in the image, not the ppi that matters. Given enough pixels, any ppi can be converted to 300ppi to achieve 150dpi printing. If you create a 72ppi image at 3600 PIXELS by 3600 PIXELS, it will look huge on your computer screen, but you can change the ppi of the 3600x3600 72ppi image to 300ppi and it will print at 12"x12" at 150dpi.

There are two ways to change the size of an image - with resampling or without. Without resampling, changing the size of the image will not affect the number of pixels. Take our 72ppi 3600 pixel by 3600 pixel example. This is a very large image size - 50 inches by 50 inches! But change that 72ppi image to 300ppi WITHOUT resampling and the image size will change to 12" by 12" and the pixel size will remain at 3600 by 3600. That's great! But, what happens if we take a 72ppi image at 12" by 12" - that would be 864 pixels by 864 pixels. Now if we change the 72ppi to 300ppi without resampling, the pixel count will remain the same (864 pixels by 864 pixels), but the image size will change to 2.8" by 2.8"! How would we keep it at 12" by 12"? We would have to use resampling. When you resize with resampling, the program will either throw away pixels (if you decrease the ppi) or add pixels (if you increase the ppi). Increasing the ppi with resampling is usually a bad idea. If there aren't enough pixels in the image to change the ppi without resampling, there will generally be significant degradation of the image when it is resized. Take our 72ppi 12" x 12" example again. When we resize using resampling to keep the 12" by 12" and we change to 300ppi, we will go from 864 pixels by 864 pixels to 3600 pixels by 3600 pixels. That's a lot of pixels to add! Where did they come from? The resampling algorithm "guessed" and added pixels based on what was in the image originally. Sometimes the resampling won't be noticeable, but usually edges won't be kept smooth (resulting in "jaggies"), detail will be lost, and other imperfections will be introduced into the image. Sizing down with resampling is not as severe a problem. That is why we can take a 3600 pixel by 3600 pixel 300ppi image and convert it to a 500 pixel by 500 pixel 72ppi image for display on the web without too much loss from a viewing perspective.

So, why then, do digital designers generally tout that their designs are 300ppi? The answer is for ease of design and for compatibility. We know that 150dpi is good for printing, so 300ppi is the highest ppi needed. Sometimes 200ppi - or even 150ppi - could be used with satisfactory results. But when you mix resolutions, you lose the consistency of size. If an element is created to be 1" x 1" in size at 300ppi, then whenever you drag that element into another document that is also 300ppi, it will always be 300 pixels by 300 pixels and 1" x 1". But drag that 300 pixel x 300 pixel element into a 72ppi document and it will be more than 4" x 4" in size because in the 72ppi document there are 72 pixels per inch (300 pixels is a little more than 4 times 72, so it would be a little more than 4 inches). The de facto "standard" is 300ppi to keep scrappers from having to constantly resize elements, and to keep the optimum resolution for printers.

This is a confusing concept that is widely misunderstood. We hope this article has helped clear it up for you! Remember, it is the number of pixels in the image that determine the print quality and 300ppi is the "standard" because there are enough pixels in a 300ppi 12" x 12" image to print at 150dpi - which is a good resolution for quality prints. As always, if you have any questions or comments about what we've covered, please feel free to contact us!

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