Snap to image edges using Magnetic Lasso tool

Select the Magnetic Lasso tool from the toolbar.

Select one of the selection modes in the Options bar.

Set the following settings in the Options bar.

• Feather: Soften the edges of a selection by gradually fading it into the surrounding pixels.
• Anti-alias: Smooth the selection boundary by blending the edge pixels with the background.
• Width: Define how far the tool detects edges from the pointer.
• Contrast: Adjust the tool’s sensitivity to edge differences in the image.
• Frequency: Control how often fastening points are automatically placed.

Select Use tablet pressure to change pen width to reduce edge width with increased pen pressure when using a stylus.

Select in the image to set the first fastening point, then drag along the edge you want to trace.

Select to add fastening points manually if the border doesn't snap to the desired edge.

Press Delete to remove recently added segments or fastening points if needed.

Close the selection border by selecting back at the starting point when the circular icon appears. If you're not at the starting point, double-click or press Ctrl + click (Windows) or Command + click (macOS) to close the selection.