Sunday, November 9, 2008

How To-56: "How to Blur the Background of a Digital Image"




How to Blur the Background of a Digital Image


from wikiHow - The How to Manual That You Can Edit

Maybe you have taken a picture of a group of people, and now you want to highlight one individual? Or perhaps you thought you've taken the perfect picture, except something in the background is distracting from the photo?Learn how to enhance your digital photos by blurring the background with GIMP or Adobe Photoshop.

Steps

  1. Use a graphic editing application such as Photoshop, Paint Shop Pro, or GIMP.
  2. Open the image file. Choose an image with a good resolution to blur the background.
  3. Determine which areas you want to stay in focus (the foreground), and what areas you want to have blurred (the background). Set the zoom to see the entire image on your monitor. This will help you get an idea of where to make your selections. To zoom in and out, use the Ctrl- and Ctrl+ keyboard shortcut in Photoshop.
  4. Click and hold on the Lasso tool (it looks like a rope lasso), then select the Polygonal Lasso tool in Photoshop. Other graphic editing applications may have this option accessible as a "point to point" feature in a "Tool Options" toolbar.
    • If the Lasso tool is not visible in Photoshop, click on the "Window" menu and select "Tools".
    • If the "Tool Options" toolbar is not visible in Photo Shop Pro, enable it from the "View" -> "Toolbars" menu.
  5. Zoom in on the image until it appears pixelated. This will give you finer control over your selection, but you may have to scroll around the image while using the tool.
  6. Select the foreground.
    1. Click once with the Lasso tool to set a point.
    2. Move your cursor to the next point to make a line, then click again.
    3. Repeat until you have a somewhat accurate selection of the foreground.
    4. Make sure the shape you create ends where you started so that the entire foreground is selected. If so desired, make multiple selected areas using the Lasso tool.
  7. Use the studio quality method to create a professional result. A faster method is described later in this article.
    1. Copy the foreground selection by pressing Ctrl-C.
    2. Paste the foreground selection over top of the existing image.
    3. Select the Move tool which looks like a cursor arrow, then drag the newly pasted foreground to line it up over top of the existing image so that they match. The newly pasted foreground and the original image should match.
    4. Select the Background layer that contains the original image. This is available from the Layers toolbar. If this "Layers" toolbar is not visible in Photoshop, select it from the "Window" menu.
    5. Select the entire image by pressing the Ctrl A keyboard shortcut, or using the "Select" menu and "All" command in Photoshop.
    6. Apply a "Blur More" filter to the selection. In Photoshop, select the "Filter" menu and choose "Blur" -> "Blur More".
    7. Repeat this Blur More command until you achieve the desired effect. In Photoshop, the Ctrl F keyboard shortcut will repeat the last filter command.
    8. Alternatively, use the "Gaussian Blur" effect instead and try different pixel radius values. This will give you a deeper control over the blur effect.
    9. Flatten your image's layers by selecting "Layer" from the menu, and "Flatten Image". If your foreground appears too sharp, you may either undo some of your Blur More commands (from the "History" toolbar) and try again, or change how the two layers combine. To do this:
      • Try changing the newly copied foreground layer's "Opacity". This is visible in the Layers toolbar. A good opacity level to start at is 50%, then move up a little at a time until you find a good blend.
      • Try changing how the layer combines with other layers by changing its property, also available in the Layers toolbar. For example, try "Darken" instead of "Normal" for an artistic sketch effect.
    10. Blur the edges of your in-focus foreground using the "Blur Tool", which should be on the same toolbar as the "Lasso Tool" in Photshop.
      1. Set the blur tool's strength to somewhere around 33%.
      2. Set your brush size to a comfortable level such as a radius of 5 to 15 pixels. If you don't see a brush size option, select "Brushes" from the "Window" menu in Photoshop.
      3. Use the blur tool to touch up the outside edge of your foreground, especially where the image seems pixelated. This will help to create a sense of transition between your foreground and background that is easy on the eyes.
  8. Use the "Quick & Dirty" method if you're looking for something faster and easier:
    1. Inverse the selection by pressing the Ctrl Shift I keyboard shortcut in Photoshop, or by selecting "Inverse" from the "Select" menu. For Paint Shop Pro, this may be the "Invert" command from the "Selections" menu.
    2. Apply a "Blur More" filter to the selection. In Photoshop, select the "Filter" menu and choose "Blur" -> "Blur More".
    3. Repeat this Blur More command until you achieve the desired effect. In Photoshop, the Ctrl F keyboard shortcut will repeat the last filter command.
    4. Alternatively, use the "Gaussian Blur" effect instead and try different pixel radius values. This will give you a deeper control over the blur effect.
  9. Save your image under a different name (to keep your original separate) by using the "Save As..." option in the "File" menu.
  10. Share your new image with friends and family!

Video

This video features two ways of blurring the background of an image, plus a few tips.

Tips

  • The higher the megapixels of your camera, the better your image resolution will be. It is difficult to enhance a picture with a lower resolution.
  • Be very precise in outlining your foreground, especially when using the "Quick & Dirty" method. Otherwise, your foreground will look choppy or it will also include part of the background that may be in focus as well.
  • Before making any alterations to a photograph, make a copy, then convert the copy to 16 million colors, if it is not already set for 16 million colors. All of the algorithms in these digital darkroom programs work better in 16 million colors than in other modes.
  • When using the lasso tool, you can make the edges blend better by changing the feather amount at the top. It is normally set to 0 but you can change it to more like 3-7. It gives a softer edge.
  • This technique produces somewhat artificial looking images. If you want a more natural look, blend your blur so it truly only affects items in the background. In the example above, if the grass in front of the child were still sharp it would more accurately simulate a narrow "depth of field", which would look more natural.
  • Some digital editing programs have a feature known as zoom blur that allows you to pick a point in your image and blur out from that point.
  • Using digital editing to blur the background does not create true depth because it blurs everything in the background uniformly rather than independently based on distance from the lens. If you are using Photoshop CS2 it now offers a 'smart blur' option in the filters sections under blur. The filter takes into account the depth of field and perspective and applies more blurring to pixels it interprets as farther away and less to pixels perceived as closer to the subject. The filter is also adjustable so it is better to gradually add the effect until you have the look desired.

Warnings

  • Make sure you do not save over your original file! Once your image file is overwritten, it is gone for good if that was your only copy.

Things You'll Need

  • GIMP, Paint.NET, Adobe Photoshop, Adobe Photoshop Elements or Corel Paint Shop Pro (formerly from JASC)
  • A digital image of adequate resolution
  • A drawing tablet is also a recommended tool to make precise selections.

Related wikiHows

Sources and Citations

Article provided by wikiHow, a collaborative writing project to build the world's largest, highest quality how-to manual. Please edit this article and find author credits at the original wikiHow article on How to Blur the Background of a Digital Image. All content on wikiHow can be shared under a Creative Commons license.

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