A couple common terms used in the printing industry are dots per inch (DPI) or pixels per inch (PPI). These terms denote what kind of resolution an image has. What’s the difference between DPI and PPI? In this video, author Richard Harrington explains what DPI and PPI are and how you can work with them to get the right resolution for your image.
- DPI, or dots per inch, is a common term used in the printing industry that denotes resolution. However, if you're working in Photoshop it's actually PPI, or pixels per inch, that you care about. The two are roughly related, and understanding this resolution is important because it allows you to reassign how the picture will be printed. Let's take a look at an image. In this case, I have a Photoshop file, and I want to check the original resolution. You can see that down here at the bottom if you click, you can get some information about this file.
For example, it's currently measuring at 42 inches by about 28 inches, however, the resolution is currently set to 72 pixels per inch which would be adequate for screen but not print. To change this, we can go to the Image Size menu. Image, Image Size. And I'm going to uncheck the option here for Resample. In this case you'll see that the width, height, and resolution are all tied together.
For example, if I change this to 300 pixels per inch, you see that the width and height are resampled. Now the image would be a 10-inch print about seven inches tall. If I click Okay, you'll notice that nothing appears to change on-screen. That's because the pixel count has been preserved. But if we check the status bar here, I see that the print resolution, sure enough, has been reassigned. Now, if you need to size this to a specific resolution, you can most easily do that with the Image Size command.
You additionally have the ability to choose Resample, a technique we're going to explore next which will allow us to target a specific output size. But I'm going to click Cancel for a moment and go back to the tool we learned earlier, the Crop tool. You may recall that you have the ability to type in a specific size here. For example, if I wanted a 10 by 6-inch print at 300 pixels per inch. Now as I adjust this and decide to crop the image in here, when I press Return, the image takes on the new size.
Now if we check the Image Size command, you'll see that it sure enough is a 10 by 6-inch print still at 300 pixels per inch. So the Image Size menu is quite useful if you want to preserve the existing shape of the photo and simply reassign the resolution. However, if you need to change the shape of the photo, then combine that with the Crop tool using a width and height resolution entry. Type in your targeted entry as well as the target resolution and when you crop, the image will be shaped and resized to the desired output resolution.
Understanding the Image Resolution command is very important because as you get images ready for print, if you don't get them set to the correct resolution you won't get the results you expect when you go to print the file.
- Cropping to a specific ratio
- Fixing images that are too bright or too dark
- Dealing with exposure, color, and skin problems
- Whitening teeth and eyes
- Changing the color of an object
- Blurring a background
- Adding a vignette
- Sharpening a photo