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I use to joke that the magnetic lasso tool in Photoshop enabled you to create selections of metallic objects. Of course, that's not true. It's not even a good joke and the magnetic lasso tool actually can prove rather helpful in a variety of situations. What its actually looking for is not a metallic object for the magnet to stick to but rather contrast within the image. Let's take a look at how you can work with the magnetic lasso tool. The magnetic lasso tool is hiding underneath the regular lasso tool so if you click and hold your mouse on the button for the lasso tool on the toolbox you'll get a fly out menu from which you can select the magnetic lasso tool. The magnetic lasso tool is in essence a brush tool. We're able to sort of paint along the edge of an object in order to create a selection of that object.
On the options bar, you'll see a variety of settings for the magnetic lasso tool. Many of those settings of course are familiar from other selection tools in Photoshop. We have the option to create a new selection. To add to an existing selection, to subtract to an existing selection, or to create an intersection selection with an existing selection. We can feather this selection. I recommend leaving that option set to zero and adjusting the feathering for the selection later in your workflow. I also recommend leaving the anti-alias check box turned on.
Next, we have the Width option. As I mentioned, the Magnetic Lasso tool is essentially a Brush tool and so we can adjust the size of the brush, as it were. I'll move the mouse out over the image. You can see my circle for this Magnetic Lasso tool and I can press the left square bracket key to reduce the size of the brush. Or the right Square Bracket key to increase the size of the brush, we'll see how that width can be important in just a moment. The Contrast setting, I really don't worry about. Generally speaking, you'd have a hard time finding any difference in the behavior of the Magnetic Lasso tool with a high or low setting.
So I just leave this set to the default value of 10%. Frequency can be important. It relates to how frequently anchor points, the magnets, as it were, for the magnetic lasso tool, are placed on your image as you move around. I'll go ahead and set the value down to zero. And then I'll click and move the mouse around the image. And you can see that we're not getting very many anchor points added to the image. They're a little bit difficult to see. Placed over the top of an image but you can see the small squares attached to the selection outline.
By contrast, I'll press escape to cancel that selection and increase the frequency to 100 then when I move about the image you can quite easily see all of those little squares, the anchor points, attached to the selection that I'm in the process of creating. With a higher frequency setting, you'll get a selection that follows the shape of a jagged object a little bit more accurately. As a general rule, I'll simply leave the frequency set to the maximum value of 100. I'll go ahead and press Escape to cancel that selection once again. That takes care of the settings on the options bar.
Let's take a look at how we can work with the magnetic lasso tool. I'll go ahead and zoom in on the portion of the image I want to select. We'll start off assuming I want to select this entire lighter brick at the corner of the building. But before I start creating the selection I'll want to fine tune the size of my brush. Generally speaking, I want to use a brush that's small enough so that I don't include any other high contrast areas within the boundary of that circle but large enough that I can move reasonably quickly around the area I'm trying to select.
So I'll press the left square bracket key to reduce the size of the brush. I could also press the right square bracket key to increase the size of the brush, that looks like a reasonably good size. I'll go ahead and click to start creating my selection, and then I don't need to hold the mouse button, I'm just moving the mouse without holding the mouse button down, and I'll trace along the edge of the area that I want to select. I don't have to be especially precise, the crosshair in the center of my brush. Doesn't have to stay right on the edge, I just want to make sure that the highest contrast edge inside that circle is the edge that I want to select.
I'll continue tracing around. all the way back to my initial starting point, and once I get to that initial starting point, I can click to close the selection. If for any reason I can't find that original starting point, I can also double-click and the selection will be created with a straight line going from the position I double-clicked to my original starting point. I already mentioned that while you're in the middle of creating a selection, you can press Esc to cancel altogether if you wanted to start over, for example. But let me show you how you can also effectively clean up a selection as you're working. I'll press control D on windows or command D on macintosh to deselect my selection.
I'll then click and start moving the mouse to create my selection but lets assume that somewhere along the way I move the mouse off that edge and now I've got a problem on my hands. I need to remove some of these anchor points I've created. In order to do that, the first thing I need to do is go back to before I made a mistake. So move my mouse back to a position before I strayed. And then, I can press the backspace or delete key in order to delete the preceding anchor point. So in this case, I'll need to press Backspace or Delete several times to get back to the position before I made a mistake.
But once I've done that, I can simply continue moving my mouse along that line. Of course, with an example like this, you might be thinking you could use a different selection tool to create a great result, perhaps with even less work, and that's possiblly true, but the magnetic lasso tool does have some other utility. Let's assume we just want the darker portion of this brick. I can go down this shadow line and because there is some contrast there the magnetic lasso tool will do a very good job of following that line. So I am able to create a slection that might not be as easy to create with other tools, not impossible to create with other tools.
But not quite as easy as it is sometimes to create within the magetic lasso tool. Now one thing to keep in mind about the magnetic lasso tool is that while it's quick and easy to use, it doesn't always produce the most accurate selection edges. I'll go ahead and zoom in on a Portion of the image here. And you can see that I have a portion of my selection that went into the brick a little bit, not the most accurate result I could have envisioned. And that's something that I see fairly frequently with the magnetic lasso tool, is that it doesn't create an absolutely perfect selection.
But it enables you to create a basic selection very quickly and easily. So, generally speaking, I won't create a selection with a Magnetic Lasso tool and then assume it is perfect. Rather, I'll zoom in and clean things up, perhaps working with the regular Lasso tool, in order to perfect that selection. But it's so easy to work with the Magnetic Lasso tool and it gives me such relatively good results with very minimal effort that I'll often use the Magnetic Lasso tool to get a selection started then clean up that selection using other tools and techniques.
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