Magnetic Lasso - How To

Making selections in Photoshop is hard work. The Magic Wand is too inaccurate and the Polygonal Lasso tool far too imprecise. The Quick Selection works only with certain kind of images and the Lasso tool requires a great deal of precision. The Marquee tool, of course, is good enough only for the roughest of selections.
However, there is another tool that is not only precise, but also (relatively) easy to learn. It can create highly accurate selections with just a flick of the mouse. It works with almost any kind of image. Moreover, it requires just a few hours of practice to achieve complete mastery.
This is the Magnetic Lasso tool and it is quite possibly the most powerful, yet underutilized tools in Photoshop. We will learn everything there is to know about it in this tutorial. Try this course for more in-depth tutorials on fundamental Photoshop skills.
How to Use the Magnetic Lasso Tool?
The Magnetic Lasso tool is one of three lasso tools available in Photoshop – Magnetic Lasso, Polygonal Lasso and the simple Lasso tool.
You can find them as the third icon from the top in the toolbox.

Although fundamentally similar – each of these three tools helps you create selections – they differ broadly in function:

• Lasso Tool: Used to make freehand selections with zero assistance from Photoshop. Since freehand selections tend to be quite imprecise, you will hardly ever need to use this, except for making very rough selections.
• Polygonal Lasso Tool: Draws polygonal, i.e. angular selections. Very useful for selecting shapes with straight edges.
• Magnetic Lasso Tool: An edge selection tool that detects an image’s edges and automatically selects the pixels around them. Selections are freehand, but with assistance from Photoshop. This gives it a high degree of precision, particularly if there is some contrast between image and the background. You can think of it as a mix between the Pen tool and the Quick Selection tool.

Understand that although the Magnetic Lasso tool works on edge selection, Photoshop cannot actually see your image. To it, everything is just a bunch of pixels. So when we say that this tool works by automatically selecting pixels along the edges, it actually means that Photoshop calculates the light, texture and contrast between a range of pixels and decides what the edge is. This results in mistakes, particularly in images where the edge is blurry.
Thankfully, Photoshop gives us a bunch of options to make the most of the Magnetic Lasso.
Want even more in-depth tutorials on making selections? Then check out this course on selections and masks in Photoshop.
Magnetic Lasso Tool Options
Select the Magnetic Lasso tool from the toolbox. Be default, the Lasso tool should be visible. You will have to click and hold on its icon to see the tool selection menu pop-up.
Once you have selected the Magnetic Lasso tool, you will see a bunch of options at the top of the workspace:

These are the Magnetic Lasso tool options.
Let us examine these in a bit more detail:
Modify Selection

These are your standard selection options – create new selection, add to existing selection, remove from selection and intersect with selection. We covered these options extensively in our Rectangular Marquee tool tutorial. It works exactly the same way here.
Feather

Increase the feather value to give your selection rounded edges. Once again, refer to the Rectangular Marquee tool tutorial for more details.
Anti-alias

Photoshop has a built-in anti-aliasing feature that smoothens out edges. I highly recommend keeping this enabled.
Width

This controls the range of pixels Photoshop scans to detect the edge. The smaller the width, the finer the control you have over the selection. You can increase/decrease the width with the ] and [ keys.
Contrast

As mentioned before, Photoshop selects the edge by calculating the difference in the brightness and texture between a range of pixels. This option allows you to increase/decrease the contrast as per image requirements. If the contrast between the edge and the background is high, increase this setting. Else, decrease it.
You can increase contrast with the . key, decrease it with the , key.
Frequency

Photoshop automatically adds anchor points as you make the selection. You can change how frequently Photoshop adds these anchor points by increasing the frequency value.
Now that we understand this tool’s many options, we can use it to actually make a selection.
Want to learn how to retouch photos? This course on Photoshop beauty retouching will teach you how!
Making Selections with the Magnetic Lasso Tool
For this tutorial, we will use this image:

You can download a copy from Pixabay.
As you can see, the edges of the box are quite well defined. The box and the background are somewhat similar in color, however. This makes it difficult to use a tool like Magic Wand to select the box separately.
This is where the Magnetic Lasso tool comes in. Follow along to see how you can use this tool to make accurate selections.
Step 1
Open the image in Photoshop and select the Magnetic Lasso tool.
Step 2
With the Magnetic Lasso tool selected, click anywhere on the edge of the box. Photoshop adds an anchor point wherever you click. As you move your cursor along the edge, Photoshop will try to detect the pixel edge and add additional anchor points.

As mentioned before, you can change how often Photoshop adds these points by increasing the frequency in the tool options.
You might have noticed that selecting the right pixels is quite difficult with the default settings. To remedy this, first, zoom in to the area you want to select. To do this without de-selecting the Magnetic Lasso tool, press CTRL++. To zoom out, press CTRL+-.
To move the image while zoomed in, press SPACEBAR. This will select the Hand tool.
It is also difficult to see the exact location of the mouse pointer. To change this, hit CAPSLOCK. This will change the default cursor from this:

To this:

This cursor shows the range of pixels currently being sampled by Photoshop to calculate the image edge. You can increase this range by pressing ]. You can decrease it by pressing [, or changing width settings in tool options.

A lower cursor width equals higher accuracy. A larger width is better when you want to make very rough selections.
To sum it up, you can get better selections by:

• Zooming in to the area you want to select by pressing CTRL++ (and moving around the image by pressing SPACEBAR).
• Switching to the ‘target’ type cursor by pressing CAPSLOCK.
• Decrease the cursor width by pressing [.

With these settings, drag your cursor along the edges of the image. Click the mouse only when you want to add an anchor point manually.

Slowly work your way around the whole image, letting Photoshop select the pixels along the edges. You can undo an anchor point by pressing BACKSPACE.
Step 3
Once you have selected the entire image, click on the first anchor point to “close the loop”. This is what your final selection should look like:

We want to remove the background from the image. To do this, press CTRL + SHIFT + I or go to Select -> Inverse to invert the selection.
Press Delete to remove the background. You will be asked to choose a background color. Select a simple white background.
This is what your image should look like now:

Step 4
You can now change the background or use the box in any other image. Here, I added a background pattern:

As you can see, the Magnetic Lasso tool can be extremely useful for making fine selections. With some practice (and a lot of zooming in out), you can select the finest of details in an image.
The Magnetic Tool is one of the most important tools in Photoshop. This course on Photoshop for beginners will teach you how to use this tool, along with other Photoshop fundamentals.