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In Photoshop it's always good to know where your image is going and what it's going to be used for, because if you know this then you know how large of a file you need to work on. In this video we're going to be talking about the three most common ways to present or share your images, which are halftone, continuous tone and screen, because each one of these has different needs. When we talk about halftone we're talking about printing on the printing press. Now halftone is not continuous tone although it might start out as a continuous tone image, such as a photograph.
But along the way it's converted to a halftone pattern for the printing press. And this halftone pattern is made up of a pattern of dots. Some of these dots are large and some of them are small, and you have a pattern of dots that's unique for each one of the cyan, magenta, yellow and black inks that are used on press. When these dots are printed one on top of another, they create the illusion of continuous tone. But it's not, in fact, a continuous tone image.
If you look at anything that's been printed, like a book or, a box of cereal, especially if you look at it under a loupe or a magnifying glass, you will see the individual dots. So what resolution do you need in order to take your continuous tone image in Photoshop and convert it for the printing press? Well, unfortunately that depends, and what it depends on is the line screen that you're going to be printing to. As a general rule of thumb, you need two times the line screen or LPI. And the line screen is going to be dependent on the paper that you're going to print to.
Typically the better quality of the paper, the more expensive the print job. This is due in part to what's called dot gain. When you print on a lower quality paper, The ink tends to spread when it hits the paper and the dots tend to bleed into one another. As you can imagine, it's harder to hold the details on this lower quality absorbing paper. For example, if you're going to print to a newspaper, which is relatively inexpensive, because of the coarseness of the paper, you can't print with a very high line screen.
So you might be limited to a line screen of 85, whereas if you're printing to a really high-end magazine or a book, you might go as high as 300 line screen. So it's really important to work with your printer and decide on the quality that you can afford, and then together you and the printer can decide on the paper, and therefore the line screen. Then you'll simply double the line screen to determine the pixels per inch in Photoshop. Now the second category is continuous tone. The most common example of that would be an inkjet printer.
And an inkjet printer needs a resolution between 240 and 360 pixels per inch. This is really dependent on the quality that you want. What I would recommend is that you print the same image at 240 pixels per inch and then 300 pixels per inch. And then 360 pixels per inch. I think you'll find that most people can see the difference between 240 and 300 pixels per inch, whereas between 300 pixels per inch and 360 a lot fewer people can tell the difference. Now technically with an inkjet printer, there are of course printed dots but the printing technology is different from the printing press. So although you might still see dots when you're viewing in inkjet print under a loupe, you're not going to see the same halftone pattern that you will in an image that is printed using the printing press.
So another example of continuous tone would be printing to photographic paper. For example, if you're a photographer you might be sending images to a lab to have them printed. In this case you simply need to ask the lab what resolution they want the file to be, because they're going to know the optimal resolution for their printer. It's been my experience that they typically want 300 pixels per inch, but I would definitely work with them to see what they recommend. Finally, let's discuss if you're going to display your images on a screen such as a monitor or a tablet or a projector.
In this case the resolution of the file really doesn't matter. You can have a resolution of 72 or 150 or 300, but it's irrelevant. What matters is the total pixel count. Because each one of these devices can display a specific number of pixels. So you need to make sure that your image is at the correct size in height and width with the exact pixel count to display properly on that device. Then the resolution can be set to anything because it doesn't matter how close or far away those pixels are set to each other. Because the device is actually going to plot those pixels at a one to one relationship between the pixel in the file, and the resolution that it can display.
So in the next video we'll actually see examples of how to re-size and re-sample your image to change the resolution and image dimensions. So that you can prepare the file for any type of output device.
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