# Pixel, Resolution, Pixel Density

Daniel Weibel
Created 10 Oct 2017

Explaining three very fundamental concepts of the digital representation of visual content: the pixel, the resolution, and the pixel density.

# Pixel

Smallest discernible element of an image or screen.

In the case of an image, it’s an individual cell of the matrix of colour values that constitutes the image.

In the case of a screen, it is an individual “light bulb” of the matrix of light bulbs that constitutes the screen.

Note that in the case of a screen, a pixel has a physical size (for example, a pixel measures 0.1 x 0.1 mm). Thus, the size of a pixel of a screen directly determine’s the screen’s pixel density (PPI).

# Resolution

The number of pixels that an image or screen consists of.

Usually indicated as width x height, for example, 1080 x 1920 pixels.

In the case of an image, it is the amount of detail that the image can represent. The values of all the pixels together is the “information” that the image contains.

In the case of a screen, it is simply the number of “light bulbs” of a screen that it can use to screen content. The more light bulbs, the more details the screen is capable of screening.

# Pixel Density

The relation of the resolution of an image or screen to the physical size of the image or screen.

The most common unit for pixel density is PPI, which stands for pixels per inch.

In the case of an image, PPI can be seen as a directive for printing the image:

• If a 200 x 200 pixels image is printed with 100 PPI, its printed physical size will be 2 x 2 in
• If the same image is printed with 400 PPI, its printed physical size will be 0.5 x 0.5 in
• If the same image is printed with 2 PPI, its printed physical size will be 100 x 100 in

In each case, however, it is the same image, with the same resolution, representing the same information.

In the case of screens with similar sizes (for example phones), the pixel density can be used as an indicator of the screen’s resolution. If a screen has a higher PPI value than another screen of the same size, then it has a higher resolution, that is, more “light bulbs” (pixels).