Most will know of and have used the Erase tool but if you click and hold the button that selects this tool a menu will appear with two other erase tools in – the Background Erase Tool and the Magic Erase Tool. In this tutorial we'll be taking a closer look at the Background Erase Tool.
Top shot: How the image first looked. Bottom shot: After we used the Background Erase tool.
What does it do?
The Background Erase tool, which turns your cursor into a circle with a crosshair in it, sounds rather self explanatory but don't be fooled in to thinking all of what's in your background, if there are various tones and colours, will vanish in a few strokes, leaving your background intact. Why? Well this tool samples colours as you drag it around your photo so if you click the crosshair on blue sky (first image) it will only remove the blues you brush over in your shot. However, if you move your cursor so the crosshair now sits over a different colour, say the building in this shot, it will start removing that instead of the blue sky (second image).
Is it easy to use?
The Background Eraser is one of the easiest tools Photoshop has for removing large parts of an image. Do remember it's an erase tool though which makes it destructive so do duplicate your layer (Layer>Duplicate Layer) so you have an original copy to go back to just in case.
You can adjust the size of the tool by either right-clicking on your image or by going to the tool bar which is found towards the top of the window (the arrow in the image is pointing to it). Here you can change the Diameter, Hardness, Spacing, Angle and the roundness of the tool. There's Size and Tolerance options be these are only useful when you're not using a mouse. Most of the time you'll want to use a hard tool as if you make it too soft it can leave some of the colour you're trying to remove behind. For those of you who like shortcuts, you can use the [ and ] keys to adjust the size of your tool.
How to use it
In our example we want to remove the blue sky and leave the part of the building that's in shot behind. To do this we click the cursor so the crosshair is sat over the blue sky. By doing so Photoshop knows we want to remove this colour so when we begin to move the cursor, the blue sky will be erased.
In theory, this means we don't have to worry about erasing the building because as long as the crosshair stays over the blur part of the shot, the tool won't erase any of the building as it's not blue. This means it's easy to get close to the edges of objects of different shades without worrying you'll delete it. Of course this doesn't always happen though, as we'll explain further down the page, but there are a few adjustments you can make to ensure it does.
Making further tool adjustments
Take a look at the tool bar which can be found towards the top of the window.
How the tool samples
Next to where you can change the tool's size there are three images with eyedroppers in them.
From left to right there's the Continuous option which is selected automatically by Photoshop, Once and a Select From Background option.
Continuous is what allows you to move the cursor around your image so any area the crosshair
moves over becomes the target colour that's removed.
The second option tells Photoshop that you want it to just erase one colour, even if you brush over another colour in the shot. This will only happen for as long as you hold your mouse button down for though so don't let go mid-way as you can end up sampling and erasing another colour by mistake.
If you're having trouble sampling a particular colour you want to remove from your photo you can use the third option which tells Photoshop you want to remove the colour which matches the background colour you've selected. To select a background colour, click on the background icon which can be found under all the tools. When you do another window will open with various colours in it. Find one that matches the colour closes to the one you want to remove in your image and click OK to close the window. If it's not as exact as you'd like you can adjust the Tolerance of the tool.
The default setting is 50% and most of the time it'll work fine, however if you find some of the detail you want to keep is getting erased as it's too similar to your background just lower the tolerance level. If the background and and the area you want to keep are very different you can increase the tolerance.
By changing the Limit option you're telling Photoshop where to look for other pixels that match the colour of the one you've selected. Do make sure you have the Once sampling option selected so Photoshop doesn't sample from other colours in your shot as you move your cursor though.
Contiguous will only remove what's in the colour range you've selected that's closest to the crosshairs. What these means is if something such as a tree branch is breaking up part of the sky, Photoshop won't erase the sky that's on the other side of the tree branch even if it's under the circle the crosshair is sat in. This doesn't happen with the Discontiguous option as this tells Photoshop that it's OK to jump across the branch to reach the other part of the image that does fit in the colour range.
For this reason, the Discontiguous option is great for shots where there's lots of small spaces between what's in your foreground and background. If you were to use the Contiguous option on a shot like this (a tree against a blue sky for example) the tool wouldn't select other parts of the sky that are broken up by branches, even if the tool's circle is sat over it. However, switch to the Discontiguous option and Photoshop ignores that the branch is there, allowing you to remove lots of small bits of sky in one go without removing any branches in the process.
If you find that some of the detail you want to keep goes slightly transparent when your cursor gets near it even if you're not sampling from that colour (see where the arrow is pointing) change to the Fine Edges Limits option as this will prevent this from happening.
Protect Foreground Color
The final option in the tool bar is a tick box which is sat next to three words which says: Protect Foreground Color. By ticking this box, you can pick a colour you want Photoshop to protect or in other words, stop it erasing it. It's useful for when you have something in your shot that you want to keep that has a similar colour range to the part of your shot you're removing.
To protect a colour, select the Pipette tool and click on the part of the image which has the colour you don't want Photoshop to erase. This action will make your chosen colour become the foreground colour (which you can see at the bottom of the tool's palette) and as a result, protects it from the erase tool.