erasing backgroung image

In this Photoshop tutorial, we look at the Background Eraser Tool and how we can use it to easily remove background areas of an image. The Background Eraser is especially useful with photos that contain lots of fine detail along the edges between the foreground and background, like, for example, if you want to erase the sky in an image without first having to select all of the trees below it.

Don't let the name fool you, though. The Background Eraser really has nothing to do with erasing backgrounds, since Photoshop has no way of knowing what's considered the background in a photo and what isn't. It can just as easily be used to erase any part of an image, and that's because the Background Eraser is really a color eraser. It samples colors as you drag the tool over them and erases only those colors, leaving all other colors untouched. So if your sky is blue and your trees are green, the Background Eraser can easily erase the blue sky while leaving the green trees alone, at least until someone comes along and cuts them down, which makes it all the more important to protect them in your image.

The Background Eraser is, without a doubt, one of the best tools in Photoshop for removing unwanted areas of a photo, but it's not perfect and it does have one serious drawback. As an eraser tool, it physically deletes pixels from the image, which means they're gone for good, so you'll definitely want to either duplicate your Background layer first before erasing any pixels or work on a separate copy of your image.

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Selecting The Background Eraser

By default, the Background Eraser is hiding behind Photoshop's regular Eraser Tool in the Tools palette. To select it, click and hold your mouse button down on the Eraser Tool until a small fly-out menu appears, then select the Background Eraser Tool from the menu:

The Background Eraser can be found nested under the regular Eraser Tool in the Tools palette.

With the Background Eraser selected, your mouse cursor will change into a circle with a small crosshair in the center of it:

The Background Eraser's cursor is made up of a simple circle with a crosshair in the middle.

You can adjust the size of the circle directly from your keyboard just as you can with Photoshop's other brush tools. Press the left bracket key ( [ ) to make the circle smaller or the right bracket key ( ] ) to make it larger. You can also adjust the hardness of the edges by adding the Shift key. Press Shift+left bracket ( [ ) to make the edges softer or Shift+right bracket ( ] ) to make them harder. In general, you'll want to use hard edges with the Background Eraser, since soft edges can leave many background artifacts behind.

How The Background Eraser Works

Before we look at a real-world example of the Background Eraser in action, let's take a more basic look at how it works. Here's a simple image made up of nothing more than a few blue and green vertical columns:

Another Photoshop masterpiece.

If we take a quick look over at the Layers palette, we see that the image is sitting on the Background layer, which is usually the case when we first open an image in Photoshop:

The original image on the Background layer.

Let's say I want to erase the blue column in the middle of the image. The way the Background Eraser works (by default, anyway) is that Photoshop samples the color that's directly underneath the small target symbol in the center of the circle. The larger circle surrounding the target symbol represents the area where Photoshop will erase pixels. Any pixels inside the circle that match the color of the pixel directly under the target symbol will be erased.

To erase the blue center column, I'll move the circle into the blue area, making sure that the target symbol in the center of the circle is directly over the blue color I want to erase. When I click my mouse button, Photoshop will sample the blue color under the target symbol and then erase all of the blue pixels that fall within the larger circle:

Photoshop erases all of the pixels inside the circle that are the same color as the pixel under the target symbol in the center.

To erase more of the blue column, I just need to continue holding my mouse button down while I drag the Background Eraser over more of the area I want to erase. Notice that even though the circle sometimes extends into one of the green columns on either side of the blue column, they remain untouched since those pixels are not the same color as the color I'm erasing. This makes it easy to get right up along the edges of the area I want to erase. As long as I keep the small target symbol inside the blue area, Photoshop will only erase blue pixels:

You can move the circle into other colors in the image without erasing them as long as you keep the target symbol away from them.

If I accidentally move the target symbol over one of the green columns, though, Photoshop will sample the green color and start erasing green pixels:

Moving the target symbol over a new color causes Photoshop to change the color that it's erasing.

If you do make a mistake like this, simply press Ctrl+Z (Win) / Command+Z (Mac) to undo it. If you need to undo multiple steps, press Ctrl+Alt+Z (Win) / Command+Option+Z (Mac) repeatedly.

The Background Layer
Notice the checkerboard pattern that appears in place of the areas I've erased. That's Photoshop's way of representing transparency on a layer, which, if you're familiar with Photoshop, may have you wondering what's going on here. A moment ago, we saw that my image was sitting on the Background layer. Photoshop treats Background layers differently from normal layers, with different rules for what we can and can't do with them. One of the things we can't do is erase pixels on them, since transparency is not allowed on a Background layer (after all, it's the background, and not being able to see through it is part of what makes it a background). How, then, did I manage to erase the pixels? Is there some sort of "Extra Strength" setting for the Background Eraser we haven't looked at yet?

Nope. What's happened is that Photoshop assumed I knew what I doing (not always the best assumption to make) and, rather than tossing up an error message complaining that I can't delete pixels on a Background layer, automatically converted the Background layer into a regular layer, which it named "Layer 0". This isn't anything terribly important, but it's still good to know what's going on:

When using the Background Eraser on the Background layer, Photoshop converts it to a normal layer.

Here's an example of the Background Eraser in action. As I make my way around the tree in the photo, the Background Eraser has little trouble erasing the blue sky while leaving the tree itself untouched, as long as I keep the target symbol over the sky and away from the tree:

Even though the Background Eraser extends into the tree, only the blue sky is erased.

However, if I slip and move the target symbol over the green color in the tree, Photoshop starts erasing the tree, in which case I'd need to undo the last step and try again:

Photoshop has no idea what the sky or a tree is. It cares only about the color under the target symbol.

So far, we know that Photoshop samples the color directly under the target symbol in the center of the Background Eraser's cursor, then it erases any pixels of that same color that fall within the larger circle. We also know that if we move the target symbol over a different color as we're dragging the Background Eraser around, Photoshop will sample the new color and use it as the color it should be erasing. What we've just described here is the default behavior of the Background Eraser, but it's not the only way the tool can behave. So how do we change things? We do that using the settings and options found in the Options Bar, which we'll look at next!

Posted in: photo editing