Steps:
1. Select the Subject: Use the Magnetic Lasso Tool (L) to carefully select the subject of your portrait. The magnetic lasso will "snap" to the edges of the subject as you trace it, making selection easier, especially on images with defined edges. Be patient and precise; a good selection is crucial for a clean result. Zoom in to ensure accuracy.
2. Refine the Selection (Optional but Recommended): Once you've made your initial selection, you'll likely need to refine it. Use the following tools for better accuracy:
* Refine Edge: Go to `Select > Refine Edge`. This opens a dialogue box with many options to perfect your selection. Experiment with the settings (Radius, Smooth, Feather, Contrast, Shift Edge) to achieve the best result depending on your image's complexity. A small feather radius can help prevent harsh edges later on.
* Lasso Tool Variations: If the Magnetic Lasso isn't giving you enough precision, switch to the Polygonal Lasso Tool (straight lines) or the regular Lasso Tool (freehand) for specific areas.
3. Invert the Selection: Once you have a satisfactory selection of the *subject*, you need to select the *background*. Go to `Select > Inverse`. This will select everything *outside* of your subject.
4. Blur the Background: Now that the background is selected, you can apply the blur:
* Gaussian Blur: Go to `Filter > Blur > Gaussian Blur`. Adjust the Radius slider to control the amount of blur. A higher radius creates a stronger blur. Preview the effect to find the desired level of blur.
* Other Blur Filters: Explore other blur filters under the `Filter > Blur` menu, such as "Motion Blur," "Radial Blur," or "Lens Blur" for different blurring effects. Lens Blur offers more realistic bokeh (the aesthetic quality of the out-of-focus areas).
5. Deselect: Once you've applied the blur, go to `Select > Deselect` (or press Ctrl+D/Cmd+D) to remove the selection.
Important Considerations:
* Image Resolution: Higher resolution images generally produce better results.
* Hair: Hair can be tricky to select. You might need to use the Refine Edge tool extensively and possibly manually clean up any stray selections using the Eraser tool.
* Complex Backgrounds: For very complex backgrounds, consider using alternative selection methods like the Quick Selection Tool or the Object Selection tool followed by Refine Edge for more efficient and accurate selections.
* Layer Masks: For even more control, consider creating a layer mask instead of directly blurring the background. This allows you to non-destructively edit the blur effect later. After making your selection, create a new layer, then add a layer mask to the new layer. Paint black on the layer mask to hide the background blur where needed, or use white to reveal more of the blur.
By combining the Magnetic Lasso Tool's selection capabilities with Photoshop's powerful blurring filters and refinement tools, you can effectively blur the background of your portraits. Remember that practice and patience are key to mastering these techniques.