From the course: Photoshop 2024 Essential Training

Making sense of document size - Photoshop Tutorial

From the course: Photoshop 2024 Essential Training

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Making sense of document size

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- [Instructor] In Photoshop, it's always good to know the final destination of your image. For example, it's good to know how your image is going to be displayed because if you know this, then you'll know the dimensions of the document that you need to work with. In this video, we're going to discuss the four most common ways to display your images on screen, halftone printing, inkjet printing, and continuous tone printing. So first, let's discuss the dimensions of a document that will be displayed on a screen such as a monitor or a phone. What's most important in this scenario is the width and height of your document in pixels. All screens have a specific number of pixels, so your document needs to have enough pixels to fill the portion of the screen where the image is going to be displayed. The resolution of the file, the pixels per inch or pixels per centimeters really doesn't matter because the device is going to map a single pixel in the document to a single pixel on the screen. If the image has too many pixels, it may appear too large, and if there are too few pixels, it might appear too small. In some instances, the image might be resized by the device and the image might appear pixelated. If it has to be resized larger than the original file, if the image will appear on a screen such as a monitor, it'll probably need to have a lot more pixels than if it's going to appear on a small mobile device. The key is to know the total pixel count for the device or for the portion of the device where you want your image to appear. Now with that said, I should mention that today many technologies that display images on screen can detect the screen size of the device that the content is being viewed on, and it will actually change the images size on the fly as the image is downloaded to the device. This technology is referred to as responsive design, and it's really powerful because it allows us to upload a single image size for the largest screen that we think it'll be viewed on. And then the software takes care of downloading the appropriate size image when the viewer clicks on the page or within the app. Now, what about halftone printing? The most common example is the printing press. Although the image might start off as a continuous tone, a photograph, for example, in order to be printed to most conventional printing presses, the document needs to be converted into what's called a halftone pattern. The halftone pattern is made up of dots with a unique pattern for each of the cyan, magenta, and yellow and black inks. When the dot patterns are printed, one on top of another, they create the illusion of continuous tone, but it's not in fact a continuous tone. If you look at anything that's been printed like a poster or a box of cereal, especially if you look at it underneath a magnifying glass, you will see the individual dots of the half tone. So in Photoshop, in addition to knowing the width and height of your document that you're going to want to print, you also need to know what resolution or how many pixels per inch or pixels per centimeter you need to print the quality of the image that you want, and that depends on the line screen that you're going to be printing to. So on press, the line screen is heavily dependent on the quality of the ink and the paper that you're printing on. And this is due in part to what's called dot gain. So when you print on a lower quality paper, the ink tends to spread out when it hits the paper and the dots tend to bleed into one another. If we look at a newspaper as an example, because of the coarseness of the paper, you can't print with a very high line screen because the dot gain makes it difficult to hold the details because those dots spread. So you might be limited to an 85 line screen for a low quality paper. Whereas if you're printing to a high-end paper for a high quality fine art book, you might be able to print as high as a 300 line screen. So as a general rule of thumb, you need one and a half to two times the line screen, which is also referred to as LPI in pixels per inch, or PPI. For example, if you're printing to a 100 line screen, you're going to need between 150 and 200 pixels per inch. But with that in mind, when you're preparing documents to be printed to the printing press, it's really important to work with your printer because together you'll decide on a line screen based on an ink and paper combination. And then from there you can decide if you want one and a half or two times the line screen to achieve the quality that you're looking for in your printing. All right, next is inkjet printing. So inkjet printers also print dots on paper, but if you look at the print under a magnifying glass, you're not going to see any halftone patterns. And this is because inkjet printers vary the placement of very, very small dots of ink on paper, inkjet printers do use cyan, magenta, yellow, and black, but many also have additional inks like light blacks or darker cyan and magenta's just to increase the numbers of colors that they can print. And an inkjet printer typically needs a resolution between 240 and 360 pixels per inch, depending on the desired quality of the print. So I would recommend that you do a test and you print the same image at 240, 300 and 360 pixels per inch. I find that most people can see the difference between 240 and 300, where the 300 pixel per inch image will look as if it's higher quality, but fewer people can see the difference between 300 and 360 pixels per inch. Of course, the viewing distance will also make a difference. If the viewer is an arms distance away from the image, then you may need to print a a higher resolution than if they're going to view the print from across the room. So what about continuous tone printing? Well, printing to a photographic paper would be an example of continuous tone printing. If you're a photographer, you might be sending images to a color lab to have them printed. In this case, you simply need to ask the color lab what resolution they want the file, because they're going to know the optimal resolution needed for their printing technology. Personally, it's been my experience that they typically want about 300 pixels per inch. So in summary, if you're creating images for screen, you need to know the total pixel count for the area of the device that you're displaying your images on. For the printing press, your document will need to be one and a half to two times the line screen or LPI in resolution pixels per or PPI. For inkjet printers, you will most likely use a resolution between 300 and 360 pixels per inch. And for continuous tone printing, it's really best to ask the lab what resolution it recommends. In the next video, we're going to see how to change the document size in Photoshop for a specific display and output device.

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