Removing Backgrounds, Part 4: The Extract Filter

The final installment of our four-part series covers the Extract filter, a powerful tool to remove backgrounds

The Extract tool was added to Photoshop back with version 5.5, and by version 7 it had been moved to the Filters menu (it used to reside in the Edit menu). It was added in order to fill Photoshop users’ need to extract backgrounds from finely-detailed images, such as ones that are made difficult by hair, leaves and other very tough details in the foreground object. Applications such as Corel’s Knockout are still around to help users tackle these difficult images, but the Extract filter actually fills the role very well. The interface is a bit complex and unintuitive in my opinion, but if you get used to it you’ll find the Extract filter a lifesaver for those images that no other tool can touch.

When to use Extract

In my Removing Backgrounds series we’ve established that the Background Eraser tool is designed to remove pixels of a certain color, the Magic Eraser tool to remove pixels of similar value and color, and the Magnetic Lasso for removing backgrounds that have a high-contrast edge around it. The Extract filter is successful at removing backgrounds where none of these are present, and is designed to be especially effective when the foreground object has hair, leaves, blurry edges or other wispy elements that blur the boundary between foreground and background. Hair and fur is the big reason the Extract filter is around in the first place—there’s so many times when a designer is asked to remove a background from a model shot or portrait, and hair is always the number one problem because of loose strands or even a full windblown look.

Figure 1: A prime candidate for the Extract filter.

Figure 1 is a great candidate for the Extract filter. The background is a mish-mash of high-contrast and low-contrast areas, varying colors and no flat areas of value or color. None of the other tools will be a silver bullet, so turning to the Extract filter makes sense.

Extract’s interface

Figure 2: The Extract filter interface.

The Extract filter is unusual among Photoshop’s tools in that it has a massive dialog box that is one big interface with its own tools and options. Something similar would be Photoshop’s Save To Web dialog box. Figure 2 shows what you will see when you select Extract from the Filter menu or by pressing Opt-Cmd-X (PC: Alt-Ctrl-X). The tools (Fig. 3) are on the left and the tool options, extraction and preview settings (Fig.4) are on the right of the Extract dialog box.

Figures 3 and 4

The fundamental principle behind the Extract filter is that the user (1) defines where the edge should be, then (2) defines which area to keep and which to remove, and then Photoshop does the rest and allows you to preview and edit the edge definition before extracting the foreground. With that in mind, let’s look at the tools:

• The Edge Highlighter Tool is used to mark the edges of the object to be retained
• The Fill Tool is used to fill in the foreground area, defined by the Edge Highlighter tool
• The Eraser Tool can erase the edge highlight or the foreground fill area
• The Eyedropper Tool is used only when Force Foreground is checked (see below) and is used to define the color to keep when this is activated
• The Cleanup Tool is used after the initial extraction preview is made, and can remove unwanted pixels (hold Option to remove the mask and add pixels). This tool, like any othe brush tool, has opacity settings though there is no place in the interface to change them. You must use the numbers 1-9 (and 0 for 100%) to change opacity.
• The Edge Touchup Tool, like the Cleanup tool, is used while previewing the extraction. It is used to clean up the edges of the extraction, in case any stray pixels are left over. Pressing the Cmd key (PC: Ctrl) will move the entire edge, and like the Cleanup tool opacity can be changed with the 1-0 keys.
• The Zoom Tool is used to zoom in and out of the image display
• The Hand Tool is used to move the image display

The Tool Options on the right side of the Extract dialog box are used to control the fill and edge highlight. You can change the color of the edge highlight and fill, but what’s more important here is the Brush Size setting and Smart Highlighting checkbox. As with other brush tools you can use the left and right bracket keys to change brush size, and you will probably want to do so in the middle of a highlighting job as a single foreground object may have many different edges, from blurry to sharp. Smart Highlighting is a great option and I use it when a foreground object’s edge is pretty easy to follow. Checking the Smart Highlighter checkbox will put a crosshairs in the Edge Highlighter brush and Photoshop will snap the edge highlight as you trace the foreground object. It’s not worth much if the object’s edge is fuzzy or blurry, but if the edge has high contrast then Photoshop should do a good job of tracing it. The rule of thumb is that if the Magnetic Lasso would follow the edge, Smart Highlighting probably will too.

The Extraction options will help Photoshop make the extraction:

• The Textured Image checkbox can be used when your foreground object has texture. Photoshop will help make a better extraction.
• The Smooth setting can be used to “smooth out” the extraction and get rid of artifact pixels around the extracted object. I wish this setting would work during an extraction preview, but it doesn’t; you have to reset, change the setting and try again.
• The Force Foreground checkbox will extract pixels of a certain color from a highlighted area (excluding any fills). The foreground color can be selected with the Eyedropper tool. I find this option to be pretty useless because it isn’t extracting an object, just pixels of a certain color. See Figure 5 to see what comes out of it. If you use a gargantuan brush size It can make some pretty interesting textures though.

Figure 5: What good is this?

The Preview options are useful for after you have made your extraction preview. You can show the extracted or original image, display the extraction preview with a variety of mattes behind it (to see how the extracted object will look on different backgrounds) as well as the mask for the extraction, and you can show highlights and fills during the extraction preview, which are normally removed after the preview is made.

Let’s Try It Out

Step 1: Select Filter -> Extract… or press Opt-Cmd-X (PC: Alt-Ctrl-X). The Extract filter dialog box opens.

Step 2: With the Edge Highlighter Tool selected and a brush size of 20, start highlighting the edge of the foreground object. The key is to make sure you get both a piece of the foreground object and background within your highlighter. For sharper edges you can use a smaller brush or even Smart Highlighting, though for this image a regular brush works pretty well. See Figure 6 for a screenshot of the Edge Highlighter Tool at work.

Figure 6: Highlighting in action.

You’ll see how I highlight every strand of hair and, when they’re in a group, I highlight the whole group including the background showing through. Using the Edge Highlighter Tool can be labor-intensive and painstaking, but the more time you spend highlighting the better your extraction will be. Unfortunately, however, there’s no way I am going to get the lamb’s hooves back with the Extract filter!

Step 3: After highlighting the perimeter of the foreground object, use the Fill Tool to fill in the foreground object. Figure 7 shows the result.

Figure 7: Filled and ready to extract.

Step 4: Make sure your settings, such as the Smooth and Textured Image settings, are where you want them. The Extract interface does not allow for changes after a preview has been created. I decided to set the Smooth setting to 15 in this tutorial.

Step 5: Hit the Preview button to get your extraction preview. Mine is shown in Figure 8, and it doesn’t look half-bad. There are a couple places where hair was wrongly extracted. Tip: Use a matte in the Preview options to make things easier to see. Photoshop leaves transparency behind the object by default, but here I used the black matte to show things clearly.

Figure 8: The preview.

Step 6: With the Edge Touchup Tool, go over any incorrect edges to clean them up. It’s a tough chore, though. It’s easy to click on stuff you want to delete, only to bring back the pixels around it. Not only that, but there is only one level of Undo in the Extract filter dialog box! I guess the programming team who created Extract didn’t get the memo from Adobe that multiple undos are the norm nowadays. Figure 9 shows my image just before committing to the extraction, with retouched edges circled.

Figure 9: Ready to extract.

Step 7: When the preview is satisfactory, click OK to commit to the extraction. Photoshop will run the Extract filter and return the image (Fig.10) with transparent background (the matte used in the preview is not kept). Insert whatever background you like and you’re done!

Figure 10: The extracted lamb!

This concludes this four-part series on extracting backgrounds. Next month we’ll have a series that touches upon another tutorial I did a few weeks ago on isolating objects for line art production. This series will deal with isolating objects using color selection tools such as Color Range, Hue/Saturation and layer blending modes. And in January we’ll have a three-part series on straightening buildings using a couple old techniques as well as Photoshop CS2′s new Lens Correction filter.

SERIES INDEX

Part 1: The Background Eraser Tool
The Background Eraser tool removes backgrounds according to color, which makes it useful for images where the foreground object and background object have different color hues.

Part 2: The Magic Eraser Tool
The Magic Eraser tool is a combination of the Eraser and Magic Wand tools, which makes it valuable in situations where backgrounds have a uniform color and value.

Part 3: The Magnetic Lasso Tool
The Magnetic Lasso tool seeks edges with high contrast, making it a tool that can snap to a foreground object’s edges quickly in order to remove the background.

Part 4: The Extract Filter
The Extract filter is a complex tool for eliminating the toughest backgrounds, including those dealing with hair, fur, leaves and blurred edges.