“Edge Contrast” is an option of the Magnetic Lasso tool, and used to be one in the Magnetic Pen tool before it was absorbed into the Freeform Pen tool’s options. Edge contrast refers to the amount of contrast between two pixels within an image, and is used by the tool to determine where to snap into place. A higher Edge Contrast setting will increase the contrast necessary for the tool to snap toward it.

If you are using the Magnetic Lasso tool on a high-contrast image, a high Edge Contrast setting will ensure the tool snaps to the most pronounced edges.

For more information on the Magnetic Lasso tool, [1] click here for my review of the tool and a tutorial.