05 August 2010 ~ 0 Comments

Pixels and DPI: What Is The Difference?

When looking at images on a desktop or Internet browser, you may notice different figures alongside the image, displaying the screen resolution and the DPI. But what are these figures, what do they mean, and what is the difference between them?

Pixels are a very basic unit used to measure computer imagery, and have been a general term associated with computer systems and processes for a long time. It is present in every aspect of computing where an image is displayed, including pictures, and the screen itself, all measured in pixels.

The problem with pixels, though, is that it does not exist in the physical world and there is no direct correlation to any physical quantity. DPI, meanwhille, stands for dots per inch, and provides a link between the computer and physical world often trading quality for size or vice-versa.

The basic formula involved with these factors is that, increasing the number of pixels in the image while keeping the DPI the same would result in a much bigger image. When this theory is reversed, increasing the DPI count while keeping the resolution the same, would ‘shrink’ the image. The concept of pixel count and DPI are very apparent in two common devices, screens and cameras. This of course transfers to printed matter.

It has been common knowledge that in order to have a high quality image, you would need to have a very high resolution or a great number of pixels in the image in order to capture the maximum amount of data.

High resolution images don’t have much of a difference when printed in a small piece of media, but it allows you to scale the image to a much bigger media without noticeable degradation.

With screens, the difference can be seen in a similar manner to Standard Definition and High Definition TV sets. With TV sets of the same size, HD sets offer a better looking and more vibrant image than SD. This is because HD sets have more pixels in them and therefore, a higher dot per inch count. SD screens are forced to enlarge each pixel in order to fit it onto the larger screen. The bigger pixel size can then be easily distinguishable. The resulting picture from the SD would then be blocky and very unappealing.

Pixels cannot be easily added to images without deteriorating the final output; this makes it a priority to maximize the resolution of images when taking pictures. DPI can be easily changed in order to fit the desired size later on. This makes it less of a priority as long as the resolution is high enough.

To Summarise:
– Pixels are the unit of computer images, while DPI translates how big the image is in the real world
– As you increase the number of pixels the image size increases but as you increase the DPI count, the image size decreases
– To maintain the quality of the image, you would need to have a high DPI count which means that a higher pixel count is needed for larger images

Overall, this means that DPI can be easily increased, but the number of pixels can only be increased by a certain amount before the overall image quality deteriorates. It is important to know about this when preparing an image to send off to print, as the image may not turn out as expected if it is not properly considered.

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