Magnetic Lasso Tool is one of the most popular selection tools offered by Photoshop. From a usage point of view, it pretty much works the same way as the Standard Lasso Tool. The only difference is that with the Magnetic Lasso Tool, you do not have to be extra careful while outlining the selection as you would have to be with the Standard Lasso Tool. The Standard Tool offers no help and it is entirely to the user to manually trace around the subject which does not produce results with 100% accuracy. On the other hand, Magnetic Tool works more like an edge detection tool. As you trace around the subject, Photoshop actively searches for the edge and snaps the selection outline to the edge, clinging to it like a magnet. This edge detection works by searching for difference in color pixels and brightness values between the subject and the background.
To select the Magnetic Lasso Tool, simply click on its icon in the Tools palette. Photoshop by default highlights the last used tool in the tool bar for all categories. For example, if the last used tool was Standard Lasso Tool, this will be the one that will show in the toolbar in Lasso Tool area. To select Magnetic Lasso tool, either left click and hold for a few seconds on the lasso tools and then select from the fly menu that will appear or right click on Lasso Tools and select.
Keyboard shortcut for selecting the Lasso tool is “L” however it is the same shortcut for all the Lasso tools. If last used tool was Polygonal or Standard, pressing “L” will again reselect it. You will have to again either right click on lasso tool or left click and hold for a few seconds for the fly menu to pop up.
To make a selection using the Magnetic Lasso tool, select a starting point, left click once and then starts tracing around your subject. You do not have to keep the mouse button pressed, just click once to create a starting point and then keep outlining around your subject till you have circled back to the starting point, hence closing the selection. You will notice that as you are dragging around the edge of your subject, Photoshop will automatically detect the edges and selection will attach itself to the edge, making your job much easier.
However, sometimes even the magnetic tool will have difficulty determining the edge of your subject. The way it works is that Photoshop limits the area where the tool looks for edges. To know how large the diameter of the tool is, press the Caps Lock key on your keyboard once and you will notice that the icon of Magnetic Lasso Tool turns into a circle. This circle tells us that Photoshop is currently looking for an edge in the area that is within the circle, everything outside of it is ignored. This circle is a better icon to use while making the selection rather than the standard icon because it tells you how large the radius is that the tool is looking for an edge within. The closer you keep the cross-hair of the circle to the edge, better it will be for the tool to determine the edge of your selection.
To begin a selection, bring the circle directly over the edge of your subject and click once. You will notice a small square shaped icon added which will be your first anchor point. A thin line will stay extended out from the circle as you drag and it will keep snapping to the edge of the subject, adding more anchor points as it goes along.
If you decide to increase or decrease the size of the circle, hence telling Photoshop to look for an edge within a larger or smaller area, you can do it both before starting to or while making the selection. There are two ways to do it. One way is to set a width of the circle in the toolbar on the top. Problem with this way is that you can only do it before starting to make the selection. Hence an easier and better way is to use the left and right bracket keys on your keyboard. Left Bracket key will reduce the size of the circle and Right bracket key will increase it. Benefit of using the keyboard shortcut is that it is accessible even when you are making the selection and provides you the ability of changing the size of the circle anytime you want.
Another way to help Photoshop determine the edges is the contrast. By setting up a contrast value, you are telling the Magnetic Lasso Tool how much the difference should be between the color and brightness values of pixels to consider something an edge. You can set up the contrast value at the top of the screen. For images high in contrast, you can use a high edge contrast value however for images poor in quality or low contrast; you must keep the percentage value low.
Right next to the Contrast field is the Frequency selection field. As you make selection using the Magnetic Lasso Tool, Photoshop automatically places small anchor points in the shape of a square. These anchors points are like knots that Photoshop ties to keep the selection in place. By changing a value here, you are telling Photoshop to how often to tie these knots, or in other words make an anchor point. You can also make an anchor point manually by simply clicking on the edge of the subject as you are making the selection.
If you find an anchor point added on the wrong spot, or in other words an incorrect area selected, you do not need to start all over again. Simple press the Backspace key and you will notice that the selection will start to roll back as Photoshop deletes the anchor points. One press of Backspace will delete one anchor point. You can undo the selection as far back as you wish and make corrections.
You can temporarily switch over to Standard or Polygonal Lasso Tool while making the selection using the Alt Key. As you are drawing an outline using the Magnetic Tool, press the Alt Key and hold left click down to temporarily activate the Standard Lasso Tool. As soon as you release the Alt Key, it will switch you back to Magnetic Lasso Tool. In order to switch over to Polygonal Lasso Tool, Press the Alt key and left click once. To go back to Magnetic Lasso Tool, release the Alt key and left click again.
If you want to remove certain parts from your selection, you can also do that using the Alt Key. After the selection has been completed, Alt key performs the function of “Subtract from Selection”. Once you have drawn an outline around you subject and closed the selection, press the Alt key and make a second selection on the area you do not want to be included. There is no need to keep the Alt key pressed down, just press it before you start making the second selection and then let it go. Complete your selection around and Photoshop will exclude the area within.
If you have zoomed into an image for the purpose of making selection and need to scroll your image around inside the document window as you’re drawing the selection, you can do it by holding down your spacebar, which will temporarily switch you to Photoshop’s Hand Tool. A hand sign will appear which you can use to scroll the image as needed. Releasing the spacebar will then take you back to Lasso Tool and you can continue drawing the selection. Benefit of this feature is that you do not need to have you entire subject fit in to the screen while you draw. Zoom as much as you need, start making the selection, press the space bar when you need to scroll up or down, and continue drawing. Remember to not release the mouse button even when you have the space bar pressed. If you need to zoom in or zoom out after you have started to make the selection, press Ctrl++ on you keyboard to zoom in and Ctrl+- to zoom out.
You may want to switch to a full screen mode as you draw so that you can be as precise as possible. To do this, before starting to make the selection, press the F button on your keyboard. This will switch you to a full screen with the Toolbar still visible. Pressing the F key again will take you to a complete Full-screen mode and even the toolbar will be gone. Once you are done drawing and you selection is highlighted, press the F key again and it will take you back to the regular mode. Remember, you need to use the F key before you are start to draw or after you are done with it. This function will not be available while you are making the selection.
If you need to deselect the area you just traced around, go to Select Menu at the top and select click on “Deselect”. Alternatively, you can also use Keyboard shortcut Ctrl+D to deselect a selection. If you started a selection and then want to stop and start over, press the Esc key.