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Snapping to edges with the Magnetic Lasso tool

From: Photoshop CS5: Selections in Depth

Video: Snapping to edges with the Magnetic Lasso tool

The Magnetic Lasso tool is useful for selecting objects that have well-defined high-contrast edges. This tool does a lot of the work for you: it locates the edge of an object based on edge contrast and lays down anchor points to fasten a selection boundary to that edge. All you have to do is guide the tool near the edge of the object. You don't even have to keep your finger pressed down on the mouse as you move your cursor along the edge. This is an ideal image on which to practice using the magnetic lasso, because there's a lot of contrast between the light skull and the dark background.

Snapping to edges with the Magnetic Lasso tool

The Magnetic Lasso tool is useful for selecting objects that have well-defined high-contrast edges. This tool does a lot of the work for you: it locates the edge of an object based on edge contrast and lays down anchor points to fasten a selection boundary to that edge. All you have to do is guide the tool near the edge of the object. You don't even have to keep your finger pressed down on the mouse as you move your cursor along the edge. This is an ideal image on which to practice using the magnetic lasso, because there's a lot of contrast between the light skull and the dark background.

I'll select the magnetic lasso from the toolbox here behind the Lasso tool. I'll get the tool started by clicking to set the first anchor point. Then, without pressing down on the mouse, I'll just move the mouse along the edge, floating it there, as it automatically sets down anchor points and lines that represent the selection border. It's doing a great job for me, until I get here, and now it's set down some anchor point that I don't want.

So, my tip for you is how to undo anchor points that you don't want. I am going to zoom in, so you see this little better. As you can see, there are a couple of anchor points on this inner line on the skull. So, to delete those, without pressing down on the mouse, I'm going to move my cursor back, and I'm going to press the Delete key, and each time I press the Delete key, I'm undoing another anchor point, as if I were unthreading. When I get back to what I consider a good anchor point, I'll try moving forward again to allow the tool to set some anchor points.

Now, I know that I am going to getting trouble here because this is a really low-contrast edge with a high-contrast dark line nearby, and it's just fooling the tool. So, there are a couple of things that I can do to perhaps help the tool along. One is that I can change the width of the brush tip. I'm going to hold the Caps Lock key and move my mouse a bit, so that you can see the width of the brush tip. This width is determining the circumference within which the magnetic lasso is going to set down points.

So, if I move along here, you can see that this black line is within the circumference of the brush, and that's why it's laying down anchor points there. So again, I'm going to back up and press the Delete or Backspace key until I get to a good anchor point. Now, I'm going to help the tool by narrowing the width of the brush tip. The best way to do that is on-the-fly, using the Left Bracket key on the keyboard. If you keep your eye in the Width field up there in the Options for this tool, you'll see that as I press the Left Bracket key, the width is being reduced.

So, now with that smaller brush circumference, let's see what happens as I move along the edge. Now, I am getting a better result. So that's one thing I can do. Another thing I can do is try to set my own anchor points along this difficult part of the edge by just clicking as I move along. So, I am clicking and clicking, and each time I do that I'm manually creating an anchor point. I am going to press the spacebar and then click and drag to move up a bit. I'll release the spacebar.

I'll show you one more thing that you can do to get past the difficult part of an edge, and that is to temporarily switch the magnetic lasso to a regular lasso and draw free-form. To do that, I am going to press down on the Option key on the Mac or the Alt key on the PC and then click and drag. You can see that my cursor tip changes, and I'm just making a free-form drawing along the edge here. When I get to an area of high contrast, again, I'll release the Option or Alt key and release my mouse.

I'm also going to make the width of the brush tip larger, so that I can be a little looser about where I'm floating the cursor; it's just easier to work with a larger brush tip. So, I'll press the Right Bracket key a few times, and now I'll continue moving along this edge. Here's another place where the brush is having trouble, so I'll back up, I'll press the Delete key, and I'll try manually creating some anchor points by clicking. I am going to zoom out, and I'll just continue along this edge without pressing down on the cursor, allowing the Magnetic Lasso tool to find the edge and set down these anchor points.

Where necessary, I'll click to set my own anchor points until I get all the way up to the top of the image. Then I'm going to hold down the Option key, the Alt key on the PC, and move my mouse to change back to the Lasso tool temporarily, so that I can just draw along this top edge. When I get back to the beginning, I'll release my Option or Alt key, and I'll release the mouse, and that completes the selection. Now, I can treat this like any other selection.

I could fill the selection with color, I could filter the selection, or use the selection for any of the other purposes that I've shown you throughout this course. Admittedly, the magnetic lasso can take a little getting used to, but if you try using it with the Caps Lock key on so that you can judge the width of the brush tip and use the Left and Right Bracket keys to change the width where necessary and set your own anchor points if need be by clicking along the edge, I think you'll come to like using this tool to select objects with high- contrast edges, like this.

Show transcript

This video is part of

Image for Photoshop CS5: Selections in Depth
Photoshop CS5: Selections in Depth

47 video lessons · 22051 viewers

Jan Kabili
Author

 
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  1. 2m 40s
    1. Welcome
      1m 12s
    2. Using the exercise files
      1m 28s
  2. 30m 22s
    1. Changing part of an image
      5m 2s
    2. Using Content-Aware Fill
      5m 31s
    3. Compositing images
      4m 18s
    4. Correcting part of a photograph
      3m 51s
    5. Replacing a sky
      4m 46s
    6. Cropping an image
      1m 8s
    7. Building an object
      5m 46s
  3. 18m 52s
    1. Understanding selections and masks
      7m 26s
    2. Deselecting and reselecting
      2m 23s
    3. Hiding selection boundaries
      3m 15s
    4. Moving selection boundaries
      2m 14s
    5. Inverting selections
      2m 9s
    6. Selecting all
      1m 25s
  4. 17m 8s
    1. Transforming selections
      3m 16s
    2. Combining selections
      7m 31s
    3. Expanding selections
      6m 21s
  5. 41m 48s
    1. Selecting hair, pt. 1
      6m 26s
    2. Selecting hair, pt. 2
      6m 6s
    3. Removing color fringe
      5m 17s
    4. Selecting an object with hard and soft edges
      6m 55s
    5. Anti-aliasing vs. feathering
      9m 9s
    6. Working with Refine Mask
      7m 55s
  6. 16m 14s
    1. Selecting rectangles with the Rectangular Marquee tool
      6m 29s
    2. Selecting ovals with the Elliptical Marquee tool
      4m 44s
    3. Selecting straight edges with the Polygonal Lasso tool
      5m 1s
  7. 18m 9s
    1. Selecting freehand with the Lasso tool
      4m 57s
    2. Selecting precisely with the Pen tool and paths
      7m 32s
    3. Snapping to edges with the Magnetic Lasso tool
      5m 40s
  8. 28m 11s
    1. Selecting painlessly with the Quick Selection tool
      5m 33s
    2. Making the Magic Wand tool work for you
      5m 23s
    3. Selecting colors with the Color Range command
      5m 39s
    4. Changing colors with Replace Color and Hue/Saturation
      5m 16s
    5. Working with the Background Eraser tool
      6m 20s
  9. 20m 55s
    1. Selecting layer transparency
      3m 31s
    2. Selecting image luminosity
      3m 47s
    3. Increasing contrast in Camera Raw
      8m 40s
    4. Fine-tuning a color channel selection
      4m 57s
  10. 17m 1s
    1. Saving selections for reuse
      6m 2s
    2. Loading and modifying saved selections
      4m 54s
    3. Sharing selections between images
      6m 5s
  11. 13m 54s
    1. Cleaning up selections in Quick Mask
      4m 42s
    2. Filtering selections in Quick Mask
      2m 34s
    3. Painting selections in Quick Mask
      2m 10s
    4. Making Step and Repeat web buttons in Quick Mask
      4m 28s
  12. 32s
    1. Goodbye
      32s

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