The 300 DPI Myth | DPI, PPI, LPI | Commercial Printing for Photographers
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Running Time: 10 minutes
What is the 300 DPI Myth? What are DPI, PPI and LPI? John Ross will explain to you the differences between Dots Per Inch, Pixels Per Inch, and Lines Per Inch. You will learn how to use them to supply images for Print magazines.
My name is John Ross with The Art of Retouching Studio. In this video we are going to cover a topic that nobody ever talks about. DPI, PPI and LPI. More specifically, dots per inch, pixels per inch and lines per inch. In the magazine and advertising industry, they throw around the acronym DPI all the time. Designers and advertisers keep telling everyone “I need that image at 300 DPI”. However, more often than not, they really mean 300 PPI.
But before I can answer where “300 DPI” actually comes from, we need to start at the beginning. So let’s do a deeper dive into what happens when your photograph makes it onto the front cover of a magazine.
Each of the items in the next section of DPI, PPI and LPI are related to printing on a press. If you think you may be doing work for a magazine or advertising agency, we need to ensure you’re able to speak the language, and supply the files correctly. The reason I talk about this is because it comes up at a later point in time when we start talking about resolution.
The first thing I want to talk about is PPI, which is Pixels Per Inch. When you look at a Non-RAW image, it is made up of pixels. Non-RAW Images, like JPGs, TIFs, and PSD’s will store all the color information on Red, Green and Blue Channels. Separately, these channels are viewed as Black and White, just like the old film days. But once the channels merge together, they give you a full color image.
When you zoom into an image really close, you will find that it’s made up of Pixels. These pixels are really tiny squares, and are made up of a single value from 0 to 255 for each of the colors Red, Green, and Blue.
Let me give you an example. In order to create the color Black, all three colors of Red Green and Blue will have a value of 0. By contrast, if you want White then the values for Red Green and Blue would all be 255. For Yellow the values could be Red:255, Green:255, and Blue:0. Any of those values could change and give you a slightly different hue for the color in question.
Whether your image is stored on the computer, or viewed on a screen, it is made up of pixels. This means Photoshop works in PPI, which is Pixels Per Inch. If you zoom in close, you can tell that your images are made up of many pixels. Each of these square pixels holds information based off of the Red Green and Blue values.
CR2, NEF, ARW and DNG are examples of the RAW file format. RAW files themselves are not made up of actual pixels. However, in order to view your Camera’s RAW files, the data needs to be interpreted and displayed on screen as Red, Green, and Blue pixels.
Photoshop works in Pixels Per Inch. Your monitor works in Pixels Per Inch, your phone works in Pixels Per Inch. Even the display on your Camera’s LCD screen will display the images as Pixels Per Inch.
When I pull up my own screen display information for this particular computer, it says that the resolution of this monitor is 3840 pixels wide. The height for the display is 2160 pixels tall. This is referred to as a 4K display. If we went down in height pixels to 1440, that is referred to as a 2K display. If we go smaller, 1920 by 1080, is simply referred to as an HD display. All of these numbers mean one thing, how many pixels are used to show on your digital display.
When it comes to your actual images, it’s basically the same thing. If you have a 24 MegaPixel Camera, your image size = 24 million pixels. If you have a 45 MegaPixel Camera, your image size = 45 million pixels.
Raw files themselves don’t “technically” use pixels as we have been discussing. But all images, even RAW, are displayed as Pixels Per Inch. Later, we will go into resolution, and that’s where we will be putting all this pixel information to good use.
This brings us around to DPI, or Dots Per Inch. DPI is exclusive to printed media.
So far we’ve only talked about working with pixels in a digital format. However, something that you’re probably more familiar with hearing, is someone mentioning DPI. They will often say they’re looking for a 300 DPI image. DPI stands for Dots Per Inch, which is different from Pixels Per Inch. This is because pixels are digital, and dots are ink on paper. I just want to be clear that conceptually they are different, yet equal.
When someone says, I want something in 300 DPI, more often than not they really mean that they want 300 PPI. Which is pixels, because that’s what you’re going to send them… a digital file. The only thing you need to know is that more than likely, if someone says that they want DPI, they probably mean PPI.
Another big difference between PPI and DPI is between digital color vs. printed color.
This leads us back to the inital question, “What are Dots Per Inch?”
Well, when you’re talking paper, you’re talking about little dots of ink. While your InkJet printer works differently than a Laser Printer or a big Printing Press, the basic concept is the same.
RGB, Red Green and Blue is how your eyes see color, and how your digital displays show color. However, most (not all, but most) printers use what is called CMYK. Cyan, Magenta, Yellow and Black. It works like this: A printer will put down a single Cyan ink dot on the piece of paper. It will then put down a single Magenta ink dot. If they are printed at different locations, you will have a Cyan dot and a Magenta dot on a big white piece of paper. However, if the printer puts down both the Cyan and Magenta ink dots at nearly the same location, then it will visually look like a single Purple dot.
So when you put down a regular spray of Cyan, Magenta, Yellow and Black onto a piece of paper, then they will interact with each other. That’s what gives us the different shades and hues of color. For an inkjet printer, it’s like a shotgun scattershot, meaning the ink is just kind of spattered all over the paper, yet it looks the way that it’s supposed to. The InkJet is not actually using DPI, rather it relies on the details provided from the PPI of the image when you hit the print button. The more pixels, the sharper the image can look, and larger the image can safely print.
When we are talking DPI, which is Dots Per Inch, we are specifically referring to a Printing Press for a magazine, newspaper, or other larger print runs. But before I finish my thoughts on DPI, we need to introduce LPI.
LPI stands for Lines Per Inch. We are actually talking about a line screen on film, or a Printing Plate. Think of it as a controlled grid for dots. InkJets, Laser Printers, and Digital Printers will go from computer, to printer, then to the paper. But unlike those types, Printing Presses use very deliberate sized dots spread out in a grid pattern. They are very small, and hard to see, but if you look up close at a cheaply printed magazine or a newspaper, you should be able to see the little dots with your eyes.
In order to print magazines that are produced in such large quantities, you need a Printing Press. This is where DPI (Dots) and LPI (Lines) are important.
The Lines Per Inch values go from a low number to a high number. Typically, 65 Lines per Inch up to 200 Lines Per Inch. The lower the Line Screen number, the lower the quality of paper. The higher the Line Screen number, the higher the quality of paper.
Let’s say we are going to print in a newspaper. The paper is very cheap, often recycled, and otherwise easy to tear. This means that if you put too much ink in one area, the ink is going to expand and bleed through the paper. Because of this, we need a controlled way of putting ink on the paper. We can do that by controlling how many ink dots we put down, and how big they actually are.
Often, newspapers will use 65 Line Screen. When we start talking about magazines, more often than not, it would be printed at a 133 Line Screen, which simply means that the paper is better. It can absorb more ink, which means we can put more dots. When we can add more dots, that ultimately means that we get a sharper looking image because those dots are smaller, and there are more of them. The result is that it’s going to be sharper and more vibrant.
When you go up to the actual front and back cover of a magazine, quite often they would use a 150 Line Screen. Because the paper used is often thicker, they can put a nice clear coating across the top and protect the ink. And so you can put a nice high quality image on the cover, and it will have a nice shine to it.
So you can have the exact same image printed in a newspaper at the lower 65 line screen (and look of poor quality), be the inside of a magazine at 133 line screen (looking good), and also be on the front cover at 150 line screen (and look stunning!). Then you have the expensive magazines that cost twice as much, like National Geographic. With higher quality papers, they can keep the Line Screen going up to 175, 200 or even higher.
Ultimately, for every quality grade the paper goes up, the more ink it can hold. This means the printer can raise the Lines Per Inch, which raises the Dots Per Inch. When they do that, the images you have printed in ads or in a magazine will look sharper and brighter.
You may not be in control of the printing quality, but you want to be sure to supply your digital PPI images at the highest quality you possibly can.
All this brings me back to why you may have heard the term “300 DPI”. I explained they really mean 300 PPI. So based on ALL the information you have now, you may still be asking “Why 300 DPI?!” The answer is actually quite simple.
Let’s say your image is going to print on the front cover of a magazine. “Great!” you say, so you only need to supply a 150 PPI file, to match the 150 LPI print, right? Wrong.
They may want your image on the front cover, but the designer only wants to use half of it. They are going to blow it up, 200%. So your 300 PPI Image is being divided in half, which means it’s actually going to be printed at 150 DPI that matches the 150 LPI. Boom. Math.
And this leads us directly into our next major topic. Bit Depth and Tonal Range. Be sure to check out that video as well.
Head on over to www.TheArtofRetouching.com to check out the RIGHT ways to use your tools, and for more in-depth videos on how to make you a better photo retoucher. Here, you can find more Behind the Retouching videos, Emergency Retouching for Beginners, as well as the Portraits, Camera Raw, and Smart Objects for the more advanced users.
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