Printers:

Pixels Vs Dots/inch:

Some printers work with pixels. A pixel is a physical area in a picture. The shape of pixels can be round, square, or rectangular. In fact pixels in many cases actually change shape a little as they are produced. A pixel carries all the color and tone (brightness) information for its place in the picture. In this way pixels are independent from each other. Some printers work with dots instead of printing uniform color and tone pixels. These printers can't lay down colors on top of each other to make a pixel so they lay down dots next to each other to make a pixel. In this case several physical dot positions make up a pixel. The dots do not stand alone representing information about the picture. Since it takes more than one dot to make a pixel with these printers dots per inch is not the same thing as pixels per inch.

Below are two giant "pixels" that serve as a rough illustration of how dots of different colors can be used to make a pixel of a certain desired color. The pixel on the right is a single uniform color across its entire area. The pixel on the left is made of a checker board style array of green and blue dots. Now most printers would not lay down the dots in such a regular pattern and they usually use cyan, yellow, magenta, and black dots. This is just to show how you can get the perception of a single color from a small area that is really made up of a bunch of dots with different colors. Depending on the resolution of you monitor these giant pixels may appear so large that you can see the dots in the one on the left. If that's the case, just stand back from your monitor some distance so you can't see the individual dots anymore and the two giant pixels should appear to be about the same color.

I say about the same color because there are a number of things that can effect how you actually see the two giant pixels. These factors in how you see the colors include things like your monitor, the ambient light where the monitor is, and how you as an individual see color. In addition, most of the time the dots these printers make are very tiny and most people would need to use a magnifier of some sort to see the dots in a printed image. Usually, people do not have pictures made with different kinds of printers to make side by side comparisons. As a result the differences in the printing process are not a concern.

The main point I am making here is that pixels and dots are not the same thing. When you see device specifications where some are in say "dots per inch" and others are in "pixels per inch", be aware that these are not the same. Usually more than one dot is required to represent a pixel so for a given number of pixels, you need a larger number of dots to create the image. Comparing dots per inch with pixels per inch can even get more complicated because some printers vary the number of dots printed for image pixels depending on the color and tone of the pixel.

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