Understanding your printer

I see there is a lot of confusion about dpi.  Most people assume that if a printer claims to print 2400dpi then it will print a document with a resolution of 2400ppi.  This is NOT true.  First  I want you to understand that printer algorithms are NOT created equal.  Each printer company will have differnet algorithms to HOW the dots are laid out to make up your image.  I am going to give you a basic understanding.

First...ppi and dpi are NOT the same.  PPI refers to pixels (picture element) per inch - used for monitors and camera resolutions.  DPI refers to dots per inch -  used in inkjet printers. 

So in your image you have your pixels..each pixel is made up of a color.  All of these colored pixels combine to form your image.  Now...when you send this image to your printer, the printer will then determine how many dots it will take to make up that ONE pixel.  Three color printers actually have 4 ink colors and the paper.  Red, Green, Blue and Black, the paper is white. 

An image can contain 16 million colors (or more)...could you imagine if you had to have 16 million ink cartridges to make all those colors? WHEW that would be one BIG printer.  Thank goodness for us our printers mix the colors we have to make up the color we need, otherwise our prints would look very bland.

Let's look at RED...there are different shades and colors of red.  How do you think the printer makes these various shades of red?

WELL...considering the paper is considered the white "ink"...it takes less red ink to make the lighter shade of red than the it does to make the brighter shade of red.  Think back to mixing paints in school...the more white you added to the red...the lighter shade of red you got  (pink).  With normal inkjet printing you don't start with the red and add the white to lighten, you start with the white (paper) and add more and more dots of ink to intesify the color.  This is because most inkjet printers do not contain white ink.  So look at the colors above and imagine...you have a white drop of paint, how many drops would it take to achieve the darker red?

Now that you see it takes multiple dots to just make the RED colored pixel -  what if it were a color that required a combination of Red, Green, Blue, and Black and white?  You would need a certain amout of dots of each color to make up that specific color of the ONE pixel.

There are also printers that change the dpi based on the paper you use.  This increases their maximum dpi from say...1200dpi to 2400dpi.  HOW?  It doubles the amount of dots placed per pixel because of the "absorption" rate of the paper. 

This is just a very brief explination of the dpi of printers.  Remember each manufacturer has a different algorithm they use for thier printing.  But, hopefully this helps you to understand that when you buy a printer that says it prints 1200dpi, that DOES NOT mean it prints 1200ppi.

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Comments

[Karen B]

thanks for the summary, lisa!