The terms Dots Per Inch (DPI) and Pixels Per Inch (PPI) are commonly used to describe the resolution of an image. However, the terms do not mean the same thing and there are distinct differences between the two:
- DPI refers to the number of printed dots contained within one inch of an image printed by a printer.
- PPI refers to the number of pixels contained within one inch of an image displayed on a computer monitor.
Both PPI and DPI are units to describe the output resolution of an image when displayed on a screen (PPI) or printed out on paper (DPI). If you divide the image size (total number of pixels of the digital image) to this output resolution, you can determine the size with which the image is shown on screen or printed out.
For example: an image with 3000x2000 pixels, printed with an output resolution of 300dpi will have a print size (width) of 10 Inch (3000 pixels / 300dpi)
Much of the confusion between these two terms happens for a couple of reasons. First, even though PPI refers to the resolution of an on-screen digital image, it can also affect the quality of the final printed picture. Secondly, some professional print services request that pictures must be at a certain DPI level before they can be printed; what they normally mean is PPI, not DPI - thus, this adds to the confusion.
The term DPI is a method to determine the print size of an image on paper in regard to its image size, which is the total number of pixels in horizontal and vertical direction. Although some printing applications still use DPI, many newer printing applications instead have a setting so you can select at exactly what size (10x15 cm, 20x30 cm, or other) you want to print a photo. For printing applications that use DPI to determine the print size, increasing the DPI will make the size of the printed image smaller, while decreasing the DPI will make the size of the printed image larger.
PPI represents the resolution (pixel density) of a digital image displayed on-screen. Because it is correlated to the image size (total number of pixels), it also contributes to the quality of an image. If a digital image contains too few pixels, the picture will not have very much detail and will appear pixelated. Digital images with more pixels have better detail. The amount of PPI by a given size on the screen is determined by the image size of the photo .
- Most digital cameras will have an image size setting in the camera menu. For the best picture quality, use the highest image size setting available on the camera when taking pictures.
- Refer to the operating instructions provided with your camera for information about possible image size settings.