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Lesson 6. Masks and Channels > Extracting an object from its background

Extracting an object from its background

Applying an extraction erases the background area to transparency, leaving just the extracted object.You’ll use the Extract command on a foxtail grass image, which is set against a dark background.This command opens the Extract dialog box, where you’ll highlight the edges of the object, define the object’s interior, and preview the extraction. You can refine and preview the extraction as many times as you wish.

Use the File Browser or choose File > Open to open the Foxtail.psd file in the Lessons/Lesson06 folder.

Choose Filter > Extract.

The Extract dialog box appears with the Edge Highlighter tool () selected in the upper left area of the dialog box.

If needed, you can resize the dialog box by dragging its bottom right corner.

On the right side of the dialog box, locate the Brush Size option, and then type or drag the slider to 20 pixels, if necessary.

You can select a brush size smaller than 20 pixels in the Brushes palette, but it’s not necessary. The beauty of the Extract function is that it distinguishes between the light-colored stem and the dark background, so a few extra background pixels won’t affect the results.

Using the Edge Highlighter tool, do both of the following:

  • Drag to highlight the stem of the foxtail grass and the single leaf. (The highlighting will extend beyond the edges of the stem and leaf.)

  • Drag all the way around the tip of the foxtail, covering the entire area around the fuzzy edges of the grass. Make sure that the outline forms a closed shape around the entire tip area.


It’s OK if the highlight overlaps the edge. The Extract command makes its selection by finding the difference in contrast between pixels. You do not need to highlight areas where the object touches the image boundaries.

If you make a mistake and highlight more than desired, select the Eraser tool () in the dialog box and drag over the highlight in the preview.

Select the Fill tool () in the Extract dialog box and click inside the outlined grass tip to fill its interior. (You must define the object’s interior before you can preview the extraction.)

Highlighting edges of foxtail tip

Highlighting stem and leaves; then filling

The default Fill color (bright blue) contrasts well with the highlight color (green). You can change either color if you need more contrast with the image colors, using the Highlight and Fill menus in the Extract dialog box.

Click the Preview button to view the extraction, and do one of the following:

  • If you are satisfied with the results, click OK to apply the extraction.

  • If you want to refine the extraction, select Original in the Show menu and select both the Show Highlight and Show Fill check boxes. Continue to work with the tools in the Extract dialog box to add to or erase areas of the selection until you create a satisfactory result. (You may need to redo Step 6 after you adjust the highlighting.) Then click OK.

The Extract dialog box closes and the image window displays the extracted area. (This may be difficult to see because the color is pale and does not stand out well against the checkerboard pattern indicating transparency.)



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