Masking with Channels in Photoshop | 2 | WebReference

Masking with Channels in Photoshop | 2

Masking with Channels in Photoshop

Using the Extract command with the History palette

Cutting objects out from their original backgrounds can be a laborious task, unless the objects are well-defined or there is a clear contrast between the object and the background. The difficulty of this operation has given rise to a number of third-party plug-ins to automate the process, but Adobe adopted these functions into Photoshop's Extract tool. While the Extract tool on its own is extremely useful, it is even more effective when used in conjunction with the History palette and History brush.

Isolating difficult subjects

1 In this example, parts of the deer are particularly difficult to isolate from the background because the texture of the grass is so similar. Using the Extract command will make what would be a very tedious job far easier. Go to Filter > Extract. Using the Edge Highlighter, start to outline the deer, changing the size of the brush as necessary.

2 In some areas—as around the ears—the edge is well defined. Enable the Smart Highlighting checkbox in these areas. It will automatically apply just enough paint to cover the edge, thereby helping to maintain a clean extraction.

3 Continue to paint until you have a complete green border outlining the deer, making sure there are no gaps. Once that's done, select the Paintbucket and click anywhere within the green border to fill it.

4 At this stage, you can click the Preview button to see how the extraction will look. Here, you can see some ragged edges in places. That's where my highlighting was a little too heavy or not quite accurate enough. I have done this intentionally to demonstrate how the History palette and brush can be used to backtrack after an extraction has been made. Click OK to confirm the extraction.

5 Open the History palette if it's not already open (Window > History) and click the New Snapshot icon at the bottom. We now have two snapshots of the image: the original, which was there from the beginning, called "deer.psd;" and the new one, which I have named "extraction." The brush icon next to the original snapshot tells us that this is the active snapshot.

6 We can now use the History brush to put back any parts of the deer that have inadvertently been removed during extraction. Select the History brush from the toolbox and start to paint over any areas where parts of the deer have been removed by mistake. The bottom of the image is the largest area that needs correcting. As you paint, you are taking pixels from the original snapshot, which is currently enabled.

7 This technique can also be used to paint pixels from the new snapshot we made. I've inadvertently painted back too much from the original snapshot on the deer's chest, so I am going to reverse the process. Enable the extraction snapshot in the History palette by clicking the gray box to its left. Paint over the affected area. You are now adding pixels from the snapshot we created immediately after the extraction.

8 Using History in conjunction with the Extract filter provides a whole new level of versatility to an already powerful tool. The final image shows the extracted and cleaned-up deer placed into a more interesting and characteristic landscape. You might agree with me that although the extraction has worked well, the deer doesn't look entirely natural in the new scene. We're going to cover this next (see page 165).


Created: March 27, 2003
Revised: April 10, 2006