Resolution is the number of pixels in an image (a pixel is one of those tiny dots on your computer screen). Commonly, resolution is shown as the number of pixels in the width of an image, and then the number of pixels in the height of the image. For instance, let's say your compute display has a resolution of 1024x768 - in this instance, the display would be 1024 pixels wide and 768 pixels high.
When the two numbers are multiplied together, you get the total number of pixels in an image. The more pixels that are in an image of a particular size, the better the image looks.
In practical terms, resolution refers to the level of detail in an image. The images below simulate a low, medium and high resolution picture of a flower.
Note that resolution is independent of size--if you enlarge a low resolution video, the pixels get further away from each other and the picture looks worse. If you reduce the size of a low resolution image, the pixels get closer together and the image will probably look better.
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