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In this movie, I'm going to introduce you to a couple of terms; image size and resolution, both of which are core concepts to understanding Photoshop specifically in a larger world of digital imaging in general. Now I happen to be working in a piece of graphic artwork that I created along with my kids a few years back. And the reason we're looking at line art is because it's the best way to learn what's going on with image size. We'll be translating these concepts to photographic images later in this chapter. Now you note that I'm viewing the image at the 100% view size.
So this is a dinky file. You often hear people call such files low resolution or low res, but it's more accurate to just say they're small because the resolution value is ultimately incidental as we'll see. Now I set-up this file to serve as a kind of slide show, and if you wonder how that's happening behind the scenes here, you can go to the Window menu and choose the Layer Comps command, and you'll see a list of comps that I have created in advance. We'll be discussing layer comps in more detail in a later course, but for now, just know that they allow you to save which layers are turned on and which are turned off.
I've also set up a custom keyboard shortcut so I can advance from one comp to another. Now this image happens to measure 918 pixels wide as well as 632 pixels tall. As you know, a pixel is a colored square. So if you do the math, you find out that we have 918x632 = 580,176 pixels, which may seem like a lot. However, that's not very many pixels where a digital image is concerned. Bear in mind that a megapixel is a million pixels, and your typical digital camera captures anywhere from 10 to 20 million pixels, in some cases even more.
These values right here amount to the image size, and if you want a definition, image size describes the pixel dimensions and the total pixel count. So 918x632 would be the dimensions, the total pixel count is 580,000. Now by comparison, resolution is the number of pixels packed into a linear inch or millimeter. So for example, the resolution of this image is set to 100 pixels per inch, or 100 PPI. That means, that are 100 pixels packed into a horizontal inch, and 100 pixels packed into a vertical inch, or a total of 100x100 which is 10,000 pixels in every square inch.
Again, that may sound like a lot but that's nothing where print resolution is concerned, and we'll discuss that in more detail later. But for now, what I need you to understand is that where Photoshop is concerned, resolution applies to print only. It is meaningless for screen graphics. So in other words, if you're creating an image for the web or some other screen environment, then you don't care what the resolution value is set to, it just doesn't matter. Whereas, image size applies both to web graphics, screen graphics, print graphics, any kind of digital image out there.
And that's how the core concepts of image size and resolution work inside Photoshop.
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