Why there is no defined size of a pixel?

Question

I thought that a pixel just has one size, a picture will either have less or more pixels, depending on the resolution of a picture. But now i find out that a pixel actually has no defined size. Im kind of confused...i dont quite understand how that works...could someone please explain to me? Thanks alot for taking the time. =))

Answer 1

In its basic form, a pixel is a 2 dimensional space with color characteristics. It has no inherent size.

In a picture file, each pixel exists only as a multibit code (usually 24 or 48 bits) representing a color.

Each pixel only gets a size when it is used on a physical device, and someone has specified how many pixels per inch (ppi) should be used.

The size is related to how each physical device uses pixels. For example:

A computer monitor may be 1200 pixels and 14 inches wide. So each pixel is
14 divided by 1200 = .0117 inches.

A printer may print at 300 pixels per inch. So each pixel is
1 divided by 300 = .0033 inches.

So the same pixel can be either .0117 or .0033 inches wide, depending on which device it is being used. It may be other sizes on other devices.

To make things more complicated, we are allowed to change pixel counts and pixel density (ppi) with photo-editing software. Either of these actions change the ultimate size of the pixel when used on a physical device.

Good Luck

Answer 2

A pixel (short for "picture element") is a dot, comparable to a dimensionles point in geometry. In reality, pixels have area -- they have size, related to the area of the CCD element in the camera, or the dot pitch on your screen, of the pixels per inch on your printer. The elements on each device are different, so we collapse them to points on a grid when we acquire the image, and expand the points in a grid for display in the manner most fitting each devive.