From the course: Photoshop One-on-One: Fundamentals

Image size and resolution - Photoshop Tutorial

From the course: Photoshop One-on-One: Fundamentals

Start my 1-month free trial

Image size and resolution

“

- [Instructor] In this movie, I'll introduce you to two important topics that are critical to understanding Photoshop specifically, as well as the world of digital imaging in general. And these are image size and resolution. Now, the key player in all of this is the pixel, the square unit of color. Right now, we're looking at a digital image, a highly graphical one inside Photoshop and let's say, I go ahead and press and hold the Z key in order to access the zoom tool on the fly and then I'll drag to the right like so and notice even before I get to the 500% zoom ratio I can see that I've got square pixels inside of this image and then if I zoom in farther I'm going to see that pixel grid so, I've got white lines surrounding each and every pixel. And that is always the way things are inside Photoshop whether you're dealing with a pixel based layer or a vector-based layer or editable text or anything you're ultimately always working in these square units known as pixels. Now, the number of pixels inside an image is the image size and the number of pixels that are packed into a square inch when you print that image is the resolution. And let me show you what that looks like. I've got this slide show that I've set up using a feature called layer comps which you can investigate if you like by going to the window menu and choosing the layer comps command but you'll probably prefer to just sit back and watch this demonstration. So, notice that I've got this image open at the a hundred percent view size which you can see up here in the title tab. So, in other words I'm seeing one image pixel for every screen pixel and this image just happens to measure 972 pixels wide by 670 pixels tall, which means that we have a total of 972 times 670 equals a little more than 650,000 pixels which sounds like a big number and it would be if we were talking about say potato chips but where digital imagery is concerned this is actually a very small number of pixels. Now, this total pixel count is known as the image size and image size describes the pixel dimensions and the total pixel count. Once again, in this case 972 by 670 equals 650,000 plus pixels. And so what we have here is what's commonly known as a low resolution or for short, low res image. But that's a little bit of a misnomer because what we really have is a small image and image with a low pixel count. Now, resolution is a different animal. It's the number of pixels packed into a linear inch or millimeter so, this image just happens to have a resolution of a hundred pixels per inch and of course it doesn't have to be inch, you can measure resolution in terms of millimeters or centimeters or what have you, but it's always linear. So, in other words, in the case of this image I have a hundred pixels per horizontal inch as well as a hundred pixels per vertical inch or a total of 10,000 pixels per square inch which again, sounds like a very large number but it's actually a low resolution. And by the way, this number, the resolution value applies to print only it is 100% meaningless on screen. So, whether this image has a resolution of a hundred pixels per inch or 300 pixels per inch that's going to change the way it prints is going to look exactly the same on screen whether viewed here inside Photoshop or on the web or on any other digital display device. Now, that doesn't mean that different screens don't have different resolutions they definitely do. I'm going to go ahead and switch to this last image right here and it's based on a bunch of screenshots so, I'm going to hide the real Photoshop interface by pressing shift + F so, that we're seeing this screenshot of a Mackintosh Retina display. So, this shot happens to come from my own MacBook Pro and as you can see here we're viewing the image at the a hundred percent zoom ratio. So, again we're seeing one image pixel for every screen pixel which is the most accurate view possible. Now, this specific device happens to have a resolution of 2880 by 1800 pixels or a little more than 5 million pixels at all meaning that the onscreen resolution is about 221 pixels per inch. And you can get the same thing on a PC, on a high DPI display. However, you could be working on a device with a much lower resolution, such as 1440 by 900 which is one of the resolution supported by the monitor that I'm using now and that would give me about 1.3 million pixels in all or about 111 pixels per inch in which case the image is going to look like this on screen at the hundred percent zoom ratio. So, in other words we're going to see fewer pixels at a time and that is regardless of the resolution value built into the image itself. So, in other words we're looking at two big key concepts. Image size which affects every single digital image out there and resolution which only matters when you print your image. Now, if that went by pretty fast, don't worry We're going to be revisiting these topics over and over again throughout this chapter but for now, that's how you work with image size and resolution here inside Photoshop.

Contents