Thursday, August 24th, 2017

The Difference Between DPI and PPI

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Most people heard the term DPI. In most cases the term is used in the wrong context to express the number of pixels in a photo, the number of dots in a print or the maximum dots per inch a printer can output. A relatively new term PPI was introduced in order to resolve this wrong usage of the term DPI. In this article we will try to explain in simple words what is DPI and what is PPI and should each be used.

PPI: stands for Pixels per Inch. PPI describes the number of pixels per inch in a photo. PPI is a function of the number of pixels the camera’s sensor supports (also known as megapixels) and the size of the photo. To calculate a photo’s PPI simply multiply the page length by its width in inches. The result is the number of square inches on the page. Now divide the number of pixels the sensor supports by the number of square inches. The result is the number of pixels per square inch. All that is left to do is to find the square root of this number. Following is a table that shows the PPI for various page sizes for a 5 megapixel camera.

page size 4X6 – 456 PPI

page size 5X7 – 377 PPI

page size 8X10 – 250 PPI

page size 11X14 – 180 PPI

page size 16X20 – 125 PPI

page size 20X30 – 91 PPI

DPI: stands for Dots per Inch. DPI is really a physical characteristic of a printer. Every printer prints dots that when put next to each other comprise a photo. Each dot has a physical size. DPI is also known as the maximum resolution that a printer is capable of. Low-end printers have lower DPI while high-end printers have higher DPI. DPI is defined as the number of dots a printer can print per inch. For example if a printer supports 1200 DPI it means that the printer can print 1200 dots per inch (on both X or Y axis). When printing it is important to make sure that the DPI is higher or equal to the PPI. If the DPI is lower than the PPI the printer will not be able to fully display the high resolution of the photo. When printing a photo that has a lower PPI than DPI the printer will use multiple dots to represent one pixel. As opposed to PPI, DPI is not relative to the page size. DPI is a fixed number for a given printer.


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Where there is no vision, the people perish.
Proverbs 29:18

The earth is the LORD’s and everything in it, the world, and all who live in it; for he founded it upon the seas and established it upon the waters.
Psalm 24:1-2

He makes springs pour water into the ravines; it flows between the mountains. They give water to all the beasts of the field; the wild donkeys quench their thirst. The birds of the air nest by the waters; they sing among the branches. He waters the mountains from his upper chambers; the earth is satisfied by the fruit of his work.
Psalm 104:10-13

Look at the birds of the air; they do not sow or reap or store away in barns, and yet your heavenly Father feeds them. Are you not much more valuable than they?
Matthew 6:26

How many are your works, O LORD! In wisdom you made them all; the earth is full of your creatures. There is the sea, vast and spacious, teeming with creatures beyond number living things both large and small.
Psalm 104:24-25

Sometimes I do get to places just when God’s ready to have somebody click the shutter.
Ansel Adams

When you photograph people in colour you photograph their clothes. But when you photograph people in B&W, you photograph their souls!
Ted Grant

While there is perhaps a province in which the photograph can tell us nothing more than what we see with our own eyes, there is another in which it proves to us how little our eyes permit us to see.
Dorothea Lange

When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence.
Ansel Adams

Your first 10,000 photographs are your worst.
Henri Cartier-Bresson

You don’t take a photograph, you make it.
Ansel Adams

Beauty can be seen in all things, seeing and composing the beauty is what separates the snapshot from the photograph.
Matt Hardy

Nothing happens when you sit at home. I always make it a point to carry a camera with me at all times…I just shoot at what interests me at that moment.
Elliott Erwitt

Which of my photographs is my favorite? The one I’m going to take tomorrow.
Imogen Cunningham

You’ve got to push yourself harder. You’ve got to start looking for pictures nobody else could take. You’ve got to take the tools you have and probe deeper.
William Albert Allard

If I saw something in my viewfinder that looked familiar to me, I would do something to shake it up.
Garry Winogrand

I always thought good photos were like good jokes. If you have to explain it, it just isn’t that good.
Anonymous

Twelve significant photographs in any one year is a good crop.
Ansel Adams

It can be a trap of the photographer to think that his or her best pictures were the ones that were hardest to get.
Timothy Allen

 


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