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As you work with a variety of the selection tools in PhotoShop, you'll come across the option for anti- alias. So that begs the question, what exactly is anti-aliasing. Well anti-aliasing relates to the shape of pixels. The fact that pixels are squared and therefore have corners. And that can actually create some minor issues when it comes to creating selections. At least if those selections are not comprised of perfectly vertical or horizontal lines. So let's create a visual example of what anti-aliasing is. I'll start off by creating the selection.
I'm going to use the Polygonal Lasso tool here, so that I can create a selection that is comprised of straight lines. To access the Polygonal Lasso tool, I'll click on the button for the Lasso tool on the tool box and hold the mouse button down for just a moment. That will bring up the fly out menu associated with the Lasso tool. And from that File menu, I can choose the Polygonal Lasso tool. And I'm going to click on the image here. I have an empty canvas that I've created. That will create my initial anchor point. And then I'll just go downward. I'm going to hold the shift key though to create a perfectly vertical line. And then I'll click once again to define my next anchor point. I'll move over to the right.
Then I'll hold the shift key so that I get a perfectly horizontal line in this case and I'll click on more time and now I'll take my mouse back to my original starting point so that I'm creating a diagonal line and then I'll click on my original point in order to close out that selection. So I've created a selection here that is comprised of a vertical line and a horizontal line and a diagonal line. And all the while, you may have noticed that up on the options bar, the anti-alias check box is turned on. So whatever that anti-aliasing option does, it's doing it to this selection. To see the effect I'll go ahead and fill the selection with black. So I'll just go to the Edit menu.
And I'm going to choose fill. I'll make sure that the use pop up is set to black. And that the blend mode is set to normal. And the opacity is at 100%. And then I'll click the OK button in order to fill that selection with black. I'll then go to the Select menu and choose Deselect, so that we no longer have that selection and we can more clearly see the shape. A shape which, whether we realize it or not, reflects anti-aliasing. So let's create another triangle, this time without anti-aliasing so we can compare the difference. I'll turn off the anti-alias check box up on the Options bar. And I'm going to create another triangle that's very close to this one, so that we'll be able to zoom in and compare them side by side. So I'll click once again up here near where I started the first triangle, I'll hold the Shift key to create a perfectly horizontal line, and I'll roughly align it with the other triangle here.
I'll click to add that anchor point, and I'll move down toward the other triangle, holding the Shift key once again to create a perfectly vertical line, and then I'll click to add that anchor point, and finally come back to my starting point for this triangle. And click once more in order to create the final selection. Once again in the shape of a triangle, just flipped essentially, but it is comprised similarly of a horizontal line, a vertical line, and a diagonal line. But this time, with the anti-alias option turned off. So, I'll go to the edit menu once again and choose fill. And with my same settings, I'll click OK in order to fill that selection with black.
And then once again I'll deselect the selection. Now, zoomed out you might not be able to tell exactly what's going on, or what the difference is between these two triangles. But let's go ahead and zoom in, and get a better sense of what is going on. And admittedly, the result is relatively subtle. But I think still rather helpful in terms of understanding exactly what this anti- aliasing is. The upper triangle of course, has the anti-alias option turned off, and there you can see a very crisp, and distinct zigzag pattern. A stair step pattern, caused by the fact that this selection, of course, reflects pixels.
In other words, it needs to be identified based on actual pixel values. The selection can't cut across the pixels, because the pixels are actually what are being used to define the selection. And so, since pixels are square and therefore have hard edges that have corners, our selection, and therefore, the triangle here, reflects that shape. I'll go ahead and zoom out for just a moment, and then zoom in to the top left corner, here. And you'll notice that, along the edges, the straight lines, we don't have anywhere near as much of a difference. But let's take a closer look at the triangle that was created with the anti-alias option turned on.
You'll still see that stair step pattern you can still see the fact that pixels are at play here. We can see all of the individual little squares, but there's a difference and it's a subtle difference to be sure but it can have a very significant impact on the overall affect and that is that instead of having only black and white pixels. We now have some shades of grey in between, which help to smooth out that jagged line. You could think of it as almost blurring effect, creating a smoother appearance by blurring or averaging out some of those values.
The result is that we don't have a jagged selection edge. I'll zoom out just a little bit. And I think you'll get a much better sense of how much smoother the triangle edge is in the case because that anti-alias option was turned on. Now of course, anti-aliasing is not a significant issue for vertical lines or horizontal lines But more often than not you'll find that your selections are comprised of somewhat random shapes. And so, keeping that anti-aliasing option turned on helps to ensure very smooth results along the edges of those selections.
To be perfectly honest with you, in most cases you're probably going to blue the edge of that selection anyway. But it is still a good idea that whenever the anti-alias option is available for the selection tool you're using, you should turn it on to help ensure smoother edges for your selections.
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