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Select with the Magnetic Lasso tool

When you use the Magnetic Lasso tool , the border snaps to the edges of defined areas in the image. The Magnetic Lasso tool is not available for 32‑bits-per-channel images.

The Magnetic Lasso tool is especially useful for quickly selecting objects with complex edges set against high-contrast backgrounds.
  1. Select the Magnetic Lasso tool.
  2. Specify one of the selection options in the options bar.
    Selection options

    A.
    New

    B.
    Add To

    C.
    Subtract From

    D.
    Intersect With

  3. (Optional) Set feathering and anti-aliasing in the options bar. See Soften the edges of selections.
  4. Set any of these options:
    Width
    To specify a detection width, enter a pixel value for Width. The Magnetic Lasso tool detects edges only within the specified distance from the pointer.
    To change the lasso pointer so that it indicates the lasso width, press the Caps Lock key. You can change the pointer while the tool is selected but not in use. Press the right bracket (]) to increase the Magnetic Lasso edge width by 1 pixel; press the left bracket ([) to decrease the width by 1 pixel.

    Contrast
    To specify the lasso’s sensitivity to edges in the image, enter a value between 1% and 100% for Contrast. A higher value detects only edges that contrast sharply with their surroundings; a lower value detects lower-contrast edges.

    Frequency
    To specify the rate at which the lasso sets fastening points, enter a value between 0 and 100 for Frequency. A higher value anchors the selection border in place more quickly.
    On an image with well-defined edges, try a higher width and higher edge contrast, and trace the border roughly. On an image with softer edges, try a lower width and lower edge contrast, and trace the border more precisely.

    Stylus Pressure
    If you are working with a stylus tablet, select or deselect the Stylus Pressure option. When the option is selected, an increase in stylus pressure decreases the edge width.

  5. Click in the image to set the first fastening point. Fastening points anchor the selection border in place.
  6. To draw a freehand segment, either release or keep the mouse button depressed, and then move the pointer along the edge you want to trace.

    The most recent segment of the selection border remains active. As you move the pointer, the active segment snaps to the strongest edge in the image, based on the detection width set in the options bar. Periodically, the Magnetic Lasso tool adds fastening points to the selection border to anchor previous segments.

  7. If the border doesn’t snap to the desired edge, click once to add a fastening point manually. Continue to trace the edge, and add fastening points as needed.

    Fastening points anchor selection border to edges

  8. To switch temporarily to the other lasso tools, do one of the following:

    • To activate the Lasso tool, hold down Alt (Windows) or Option (Mac OS), and drag with the mouse button depressed.

    • To activate the Polygonal Lasso tool, hold down Alt (Windows) or Option (Mac OS), and click.

  9. To erase recently drawn segments and fastening points, press the Delete key until you’ve erased the fastening points for the desired segment.
  10. Close the selection border:

    • To close the border with a freehand Magnetic segment, double-click, or press Enter or Return.

    • To close the border with a straight segment, hold down Alt (Windows) or Option (Mac OS), and double-click.

    • To close the border, drag back over the starting point and click.

  11. (Optional) Click Refine Edge to further adjust the selection boundary or view the selection against different backgrounds or as a mask. See Refine selection edges.