However, let's cover how to do it using the Magnetic Lasso Tool and then I'll offer some better alternatives:
Using the Magnetic Lasso Tool (Not Recommended for Best Results):
1. Open your image in Photoshop.
2. Duplicate the Background Layer: In the Layers panel (Window > Layers), right-click the "Background" layer and choose "Duplicate Layer." This is a non-destructive way to work, allowing you to revert to the original if needed. Name the duplicate layer (e.g., "Portrait").
3. Select the Magnetic Lasso Tool: Find the Magnetic Lasso Tool in the Tools panel (looks like a lasso with a little magnet attached). It might be hidden under the Lasso Tool icon; click and hold to reveal it.
4. Adjust Settings (Important): In the options bar at the top, tweak these settings:
* Width: This determines how far away from the edge the tool will look for snapping points. Start with a small value (like 5-10 pixels) and adjust as needed. A higher value makes it stickier but can also stick to unwanted edges.
* Contrast: Higher contrast will help the tool snap to edges more easily. Experiment with values between 10-20%.
* Frequency: This controls the number of anchor points the tool places. Higher frequency means more anchor points, which can be helpful for complex edges but can also make the selection process slower. Start with around 50-60.
* Tablet Pressure Controls Width: *Uncheck* this unless you're using a graphics tablet with pressure sensitivity.
5. Carefully Trace the Subject: Click once on an edge of the subject (the person). Slowly move the cursor along the edge. The Magnetic Lasso should automatically snap to the edge.
* Anchor Points: You can manually add anchor points by clicking along the edge. This is helpful when the automatic snapping isn't working well.
* Correcting Mistakes: If the lasso goes astray, press the Delete key (or Backspace on Mac) to undo the last anchor point. Continue retracing until you get back on track.
* Zoom In! Use the zoom tool (Z key) to get close to the edges, especially around hair and clothing.
6. Close the Selection: When you get back to your starting point, the cursor will change to include a small circle. Click to close the selection.
7. Invert the Selection: Go to Select > Inverse (or press Ctrl+Shift+I / Cmd+Shift+I). This selects everything *except* the subject – which is what you want to blur.
8. Apply the Blur: Go to Filter > Blur > Gaussian Blur.
* Adjust the "Radius" slider to control the amount of blur. Start with a small value (e.g., 2-5 pixels) and gradually increase it until you get the desired effect. Keep an eye on the preview.
* Click "OK."
9. Deselect: Go to Select > Deselect (or press Ctrl+D / Cmd+D) to remove the selection.
10. Optional: Refine the Edge: If you see a harsh line around the subject, you can try:
* Feather: Go to Select > Modify > Feather. Enter a small value (e.g., 0.5-1 pixel) and click OK. This softens the edges. You may need to blur again.
Why the Magnetic Lasso isn't ideal:
* Hair: It struggles with selecting individual strands of hair.
* Complexity: Complex clothing details and low-contrast edges can confuse it.
* Time Consuming: It can be a very slow and tedious process to get a good selection.
Better Alternatives for Blurring Portrait Backgrounds in Photoshop:
* 1. Select Subject (Best for simplicity):
* Go to Select > Subject. Photoshop's AI does a surprisingly good job of selecting the main subject.
* Then follow steps 7-9 above (Invert, Blur, Deselect).
* Refine Edge: If the edge isn't perfect, after "Select Subject", click "Select and Mask" to fine-tune the selection, especially around hair. Use the "Refine Edge Brush Tool" to paint over the hair. Experiment with the "Smooth," "Feather," "Contrast," and "Shift Edge" sliders.
* 2. Quick Selection Tool:
* Select the Quick Selection Tool (looks like a paintbrush with a selection around it).
* Simply paint over the subject. Photoshop will automatically select the area.
* Use the "+" and "-" options in the options bar to add or subtract from the selection.
* After selecting the subject, follow steps 7-9 above (Invert, Blur, Deselect).
* Refine Edge: Use "Select and Mask" to refine the edge as mentioned above.
* 3. Channels (Advanced but Most Accurate for Hair):
* This method uses the color channels (Red, Green, Blue) to create a mask. It's more involved but provides the most precise selection, especially for hair. I won't go into full detail here, but you can find many tutorials online by searching "Photoshop Channels Selection Hair."
* 4. Portrait Mode (if available): Many photos taken on phones have portrait mode built-in, which automatically blurs the background for you. This is the easiest option if you have it.
Key Tips for Blurring Backgrounds:
* Subtlety is Key: Don't overdo the blur. A too-blurred background can look unnatural.
* Match the Blur to the Scene: Consider the original depth of field. A portrait taken with a wide aperture lens will have a more blurred background than one taken with a narrow aperture.
* Consider a Lens Blur Filter: The "Lens Blur" filter in Photoshop (Filter > Blur > Lens Blur) can simulate the bokeh of a real lens, which can look more realistic than Gaussian Blur. It's more complex to use but worth exploring.
* Practice: Experiment with different tools and settings to find what works best for you.
By using the Select Subject tool and refining the edge with Select and Mask, you'll achieve much better and faster results than with the Magnetic Lasso Tool. The magnetic lasso tool is better suited to objects with smooth, high-contrast edges, not necessarily complex portraits.