From the course: Photoshop 2024 Essential Training

Using image size to change document dimensions - Photoshop Tutorial

From the course: Photoshop 2024 Essential Training

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Using image size to change document dimensions

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- [Instructor] Let's find out how to calculate the correct document size for different types of output devices. We'll take a look at image size and then prepare this image for outputting to screen, the printing press, and an inkjet printer as well as we're sending out to a lab. Now to change the size of a document for a specific device, I'll choose image and then image size. On the left hand side we have the preview, which we can pan using the hand tool. And on the right hand side we have all of the document dimensions. We can make this preview larger or smaller, and we can also navigate to a specific location by positioning our cursor over the image preview area and then just clicking when we see the square and that area will go directly to the preview area. Alright, we can see that this file is about 30 megs, and as I start making changes, there are two ways that I can do this, depending on the results that I want to achieve. If I turn off the re-sample option, then I can make changes to width, height, and resolution, or we can change the print size of the image, but we're not adding or subtracting pixels, we're just determining how many pixels we want Photoshop to put within a specific unit of measurement. For example, if I increase the width here to 18 inches, well then the resolution has to decrease because I have a set number of pixels, and so if I'm going to make the width bigger, the resolution has to go down. Likewise, if I change the width to six inches, well then the resolution of the file can go up because again, I'm telling Photoshop it can't throw away or add any pixels to this document. If on the other hand I choose re-sample, now I'm giving Photoshop permission to add or subtract pixels from the image. If I make this image six inches, then Photoshop's going to throw away information. If I make it 18 inches, then Photoshop's going to have to add information. And I know it's adding information because we can look up here under image size, it was 30 megs, but if I want to print it this size, it's going to be 274 megs. We can also change the dimension option here to a percent if we want to see what percentage of pixels Photoshop would have to make up or throw away. In this case it's 300%, so the image might get a little bit soft. If you want to control how the image is re-sampled, we can choose from any of the different options from the list. When we use automatic Photoshop's going to use preserve details when it up samples an image, or when it makes it bigger. And it's going to use by Bicubic's Sharper when it's reducing down an image. So that's nice, we don't have to go in here and choose the two every time we use image size because Photoshop's smart enough to vary the algorithm that it uses when we have this on automatic. Of course you can always go in here and you can look at these other options and then just preview what they look like over here in the image area. Alright, let's go ahead and switch that back to automatic. Now let's quickly take a look at how I would set the image size of a document for those specific output devices. If I need to resize this for a specific screen, then I can change the units of measurements to pixels. So if I wanted this to be say, 1200 pixels, I can just enter in that value. Now if I'm going to go to the printing press, well then I can change this back to inches. And let's say on the printing press, I'm going to print with a 150 line screen, well because I want one and a half to two times the line screen and pixels print, let's say I'll just do the one and a half, so I'm printing 150 line screen, I want to multiply that by 1.5, so I'm going to get 225 pixels per inch. So let's enter that in. I'll go ahead and enter 225 for pixels per inch, but then I'm going to decrease the size or the width of the image down to 18 inches. If we look above, we can see that Photoshop's going to have to add pixels or re-sample up in order to create this file. If I didn't want to print it that large, maybe just 10 inches instead, well now we can see that Photoshop would throw away information. I have plenty of information in the original document to print at this size without any interpolation. Alright, and if I'm printing to an inkjet printer or if I'm sending this to the lab to print continuous tone on photographic paper, then I would probably want to set my resolution to 300 pixels per inch. And this time it would have to make up a little bit of information. But if you have to add 10 or 15%, I think that should be just fine. And if we go below the original size, well then Photoshop will throw away information and we'll have a great quality print. So let's go ahead and apply that. And yes, we can see that the image was reduced in size, so at this point I would want to be sure to save a copy of the file at this new size so that I could always return to the original document if I needed the larger file at a later time. And we'll learn more about saving files in another video. So for now, I'm just going to close this document without saving. So there you have it to resize your documents for a specific output device, be sure to use the image size command in Photoshop.

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