Pixel Dimensions
Here's a photo I took one day while strolling through a park. I saw this little guy (or girl, who knows) posing for me on the flowers and happened to have my camera handy. My camera, by the way, is an 8MP camera, and the reason why I'm telling you this will be explained shortly.
Obviously, the photo you're seeing above is a much smaller version of the photo, since the actual-size version would be too large to fit on the screen. Let's pretend though for the sake of this lesson that we're working with the full size version of the photo. In order to see exactly how large the photo is, once we have it open inside Photoshop, we can simply go up to the Image menu at the top of the screen and choose Image Size from the list of options, which will bring up Photoshop's Image Size dialog box, as shown below.
The Image Size dialog box can seem a bit frightening and confusing, but it's not meant to be and really, it's quite simple. It's divided into two sections, Pixel Dimensions and Document Size. For the moment, let's ignore the Document Size part and focus only on Pixel Dimensions.
The term "pixel dimensions" here, to me, is confusing because it sounds like we're talking about the dimensions of each individual pixel, and that's not the case. What Photoshop is really telling us is the width and height of our image in pixels. In other words, how many pixels are in our image from left to right, and how many pixels are in our image from top to bottom. It's also telling us one other important piece of information which is the file size of our image. The dimensions and file size shown here are of the full size version of the photo above (the insect on the flower) before I resized it to something more suitable for a web page. So here, Photoshop is telling me that my photo has a width of 3456 pixels and a height of 2304 pixels. In other words, it contains 3456 pixels from left to right, and 2304 pixels from top to bottom. To find out exactly how many pixels I have in my photo then, I can simply multiply the width times the height, which in this case is 3456 x 2304, which gives me a grand total of 7,962,624 pixels. That's a whole lot of pixels.
Remember earlier when I mentioned that the camera I used to take this photo was an 8MP camera? Well, the "MP" stands for "mega pixel", and "mega" means "million", so "8MP" means 8 million pixels. This means that when I take a photo with my digital camera
, the photo will be made up of 8 million pixels (approximately, anyway). If you have a 5MP camera, your photos will be made up of 5 million pixels. 4MP cameras give you photos made up of 4 million pixels, and so on. So if we take a look again at what the Pixel Dimensions section of the Image Size dialog box is telling us about my photo above, it's saying that my photo has dimensions of 3456 pixels wide by 2304 pixels high, for a total of 7,962,624 pixels, which is pretty darn close to 8 million, and that's why my camera can be sold as an 8MP camera.
So that's what the first part of the Image Size dialog box is telling us - the width and height of our image in pixels. So far so good. Let's take a look now at the second part of the dialog box, "Document Size" which is where we really start to make sense of image resolution.
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