What is DPI?

R. Kayne

Dots Per Inch (DPI) is a measurement of printer resolution, though it is commonly applied, somewhat inappropriately, to monitors, scanners and even digital cameras.

In the case of monitors, DPI refers to the number of pixels present per inch of display screen.
In the case of monitors, DPI refers to the number of pixels present per inch of display screen.

For printers, the DPI specification indicates the number of dots in each inch that the printer is capable of achieving to form text or graphics on the printed page. The higher this specification, the more refined the text or image will appear. To save ink, a lower concentration is often used for draft copies or routine paperwork. This setting might be 300 or even 150 DPI. High resolution starts at 600 for standard printers, and can far exceed that for color printers designed for turning out digital photography or other high-resolution images.

DPI is commonly applied to digital cameras.
DPI is commonly applied to digital cameras.

In the case of monitors, DPI refers to the number of pixels present per inch of display screen. The technically correct term is "PPI" or pixels per inch, but DPI is commonly used instead. A display setting of 1280 x 1024 has 1.3 million pixels on the screen, while a setting of 800 x 600 has 480,000, or less than half the resolution of the higher setting. With fewer pixels, the picture will not have the clarity that can be achieved with a higher saturation. Each dot or pixel reflects a certain color and brightness. The greater the number of pixels, the more detailed the picture can be. More pixels also require more memory, and it can take longer to "paint" images, depending on the system's video card, processor and other components.

Scanners also operate at different resolutions. Scan time will increase with higher DPI settings, as the scanner must collect and store more data. However, the greater requested resolution, the richer the resulting image. A high resolution, or DPI setting mimics the original image in a truer fashion than lower DPI settings are capable of doing. If the image is to be enlarged, a high setting is necessary. Otherwise the enlarged picture will look "blocky" or blurry because the software lacks information to fill in the extra space when the image is enlarged. Instead it "blows up" each pixel to "smear" it over a wider area.

Digital cameras have their own specifications in terms of megapixels and resolution, but DPI is often mentioned in this context as well. Since it in all cases refers to the output image, a digital camera capable of the most basic current standards of resolution —- 3.0 megapixels and better —- will output an image capable of taking advantage of a very high DPI setting on the printer. However, if your printer is only capable of 600 DPI, the extra resolution of the camera will be lost in the printing process. When buying or upgrading components it is therefore critical that each product is capable of supporting the highest standards of any interfacing product.

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Discussion Comments


How do I change my DPI setting?


i just don't understand how the math works on it to figure out what high res would be just to print high res. 600 dpi is that high res for printing large photos? or can you get even better high res? i guess my question is what the highest on everything resolution wise that you can go. i print at a pro lab and feel really stupid right now.


The DPI/PPI measure becomes significant when the actual geometry of the viewing experience is taken into account, since it determines how 'smooth' a given image appears when viewed. With print media, 600DPI is considered 'smooth' no matter how closely an unassisted eye is viewing an image. But computer displays are typically no closer than 18-24" from the eye; 600 DPI would be overkill, and few are more than 120PPI. Mobile displays (ebook readers, cell phones) can be brought much closer to the eye when in normal use, and need higher DPI (150 or more).


I am submitting a photo for judging. The limits are 150 dpi to 300 dpi. I have 2.21 MD and 1944 x 2592 sizes. What is that in dpi?


HELP! PC Photo is running a photo contest. Photos must be submitted electronically and be no more that 125K, 640 X 180, and 72 dpi. I don't get it. When I try to save a photo in Photoshop with these dimensions, it is about the size of a postage stamp, and any bigger, it is all pixelated and looks like crap. What am I not understanding?

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