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In this exercise, I am going to lay out the basic concept of image size inside of Photoshop. This is one of these core topics that you've got to wrap your brain around before you can make any meaningful sense of the program. So here is how it works. Image size is the dimensions of your image, that is how many pixels wide, and how many pixels tall. And we care about pixels more than the other measurements, more than inches and centimeters, and all that stuff that means something in print, but doesn't have any meaning on screen.
So this very simple concept. How wide is the image? How tall is the image in pixels? That's image size. But it begs a lot of questions. For example, how many pixels do you need? How many pixels should you capture with your digital camera? How many pixels should you be scanning? What resolution value should you use? How many pixels do you need for smooth output? What if you don't have enough? Can you add more pixels inside Photoshop? Should you ever subtract pixels or should you change the resolution value and leave the pixel count alone? And what is resolution anyway? Well, sorry to fire so many questions at you, but these are the questions that we will be answering over the course of this chapter.
Now if you are working along with me, I've got a piece of artwork for you. It's called Shepherd and small flock.tif. And when I say small flock, I don't necessarily mean a small flock of sheep. I mean a small flock of pixels, because there is not many pixels at work inside this image. Now, this is a piece of artwork I created years ago. It's a kind of murder mystery because here's the shepherd up here. Here is the skeleton on top of this arch. And then his clothes were stuffed into a scarecrow, and we have the sign that says Killer indicating that the scarecrow is the killer, but really the sheep did it.
Anyway, that's the subject of this artwork. The content is pixels. Now, we are seeing this image at the 100% zoom level, meaning Photoshop is devoting an entire screen pixel to each and every image pixel, and we're seeing almost the entire image in the Full Screen mode here, just a little bit of the perimeters being cut off. So, if we're looking at 100% then we're seeing everything there is inside this image. In other words, we're not going to find anymore detailed information inside of this artwork.
For example, if I press and hold the Z key to get the Zoom tool and then I drag to the right in order to take advantage of that scrubby Zoom function in CS5, I'm zoomed way in on the scarecrow's face and yet it doesn't look anymore like a scarecrow than it did before. We're not seeing anymore definition to the line art in other words. Instead, we're just seeing these big huge pixels divided by the pixel grid. Incidentally, if you don't know what a pixel is, it's a colored square. So each and every digital image you see is this incredibly complicated mosaic and nothing more.
In fact, you may know that Photoshop is the most popular program from Adobe. So the other teams inside Adobe like to razz the Photoshop guys about what's the big deal! All you guys do is recolor pixels. At the end of the day, that's true. Photoshop just happens to be an extremely complex, extremely powerful pixel re-coloring machine. What we need to know now is how many pixels are available to us. So I am going to go over to this I button here, and click on it to bring up the Info panel.
You can also go to the Window menu and choose Info or press F8. Now, Info is a terrific panel for analyzing an image. You can see the color of the pixel under your cursor represented in RGB and CMYK by default. But you can change those around if you want to. You can also see the co-ordinate position as measured in pixels in my case and hopefully yours as well, that XY position right there of your cursor. Then you can see the width and height of a selection outline, plus we are going to see the document size and a description of how to use the Active tool.
Although, I don't find that last item to be very helpful, but the document size is pretty helpful. We're seeing that it's 1.9 megabytes in Photoshop's memory in RAM, and that's not very large. Now, that's big for a web graphic, but it's dinky by print standards and it's definitely small enough to email to somebody, which is a good thing and it's not going to slow Photoshop down. Photoshop has no problem with 2 megabyte images like this. Anyhow, there's more information to be had, and we can get to it by clicking on this menu icon and choosing panel Options.
What I am going to do, first of all, I want to confirm that Ruler Units is set to Pixels. You'll need it to be set to pixels throughout this chapter but I recommend you have your units set to pixels always in Photoshop. Next, I'm going to turn off those tool hints because I don't find that to be helpful at all, and I am going to turn on Document Profile which is the color profile that's associated with the active image, and Document Dimensions which will be the image size itself, and then if you like to know what's going on underneath Photoshop's hood, you may want to turn on Scratch Sizes.
And that's going to tell you the size of the scratch disk file on your hard-drive. Then go ahead and click OK. Notice the tooltips have gone away. There is the scratch size and very briefly what's happening there is in the event that Photoshop tops out in RAM, you open a big image, lots of layers, Photoshop is trying to keep track of all the history, and it's too much to store all that information in memory. So it has to go to a scratch disk file on the computer's hard-drive. And the size of that file is going to change over time, but mine has grown to 1.4 gigs.
Currently, I am only taking advantage of 457 megabytes of those 1.4 gigs. Where things become a problem is if this number starts becoming very large or these two numbers are very close to each other, it's not something you should worry about. It's just something you should know in case the program is running very slowly, and when that starts happening, you might just want to restart Photoshop. You don't have to reset the preferences or anything. You might just want to restart the program in order to clear out the memory. Worst case scenario, every once in a while you have to restart your machine.
Anyway, back to the image size stuff. This image is not so big it's going to hurt anything. Next, we have the Adobe RGB (1998) profile. That's how we established our color settings long ago. Then you can see that the image measures 993 pixels wide by 668 pixels tall. Now, if you do that math, you just multiply those two numbers together. You discover that total number of pixels inside this image is 663,324, so nearly 700,000 pixels which sounds like a lot.
However, where pixels are concerned, that's not very much. Bear in mind that's not even a mega- pixel which is a million pixels, and your digital camera shoots lots and lots of mega-pixels. Next comes this value, 100 ppi, 100 Pixels Per Inch, and that's the print resolution. It only matters for print and it also happens to be a linear measurement. Meaning that an inch will contain 100 pixels wide, and 100 pixels tall. So 100x100. That is 10,000 pixels fit in a square inch.
That may sound once again like a ton of pixels but it's not nearly enough for professional printing. So what we have here is an exceptionally low resolution image. How do we go about gaining more pixels as well as gaining more clarity? Well, that's a question I will begin to answer in the next exercise.
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