Photoshop Channel Mask
It may seem like a real challenge to pull the fireworks out of this image. The selection tools won't work, and the background eraser didn't produce very good results either. I'm going to show you an amazingly simple technique for masking the fireworks in this image using the channels palette.
The total time isolating the fireworks was under two minutes. This technique doesn't always work this smoothly for every image, but it can be used in combination with other methods for making more complex selections. In the fifth example on removing backgrounds with Photoshop, you'll see how this technique was expanded on and combined with other methods for masking a more complicated image. If you're not familiar with masks, you may find it helpful to read my previous article, All About Grayscale Masks.
The first step is to look at the channels palette and determine which color channel best represents the area we want to capture. To the right, shown from top to bottom, you can see the red, blue, and green channels for this image. It's obvious that the red channel contains the most information for capturing the fireworks.
In the channel palette, click on the red channel and drag it down to the new channel button.
This creates a duplicate of the red channel as an alpha channel. Alpha channels are a way of saving selections that can be loaded at any time. In addition, they can be edited with painting tools like a grayscale mask.
Note: In older versions of Photoshop, this channel will be called Alpha 1 (assuming it's the first alpha channel). In later versions of Photoshop, the duplicated channel will be named as a copy of the duplicated channel, such as "Red Copy" in this example.
After duplicating the red channel, the white areas at the bottom of the image (from the city lights in the original image) are painted out. You want to be sure that your alpha channel is the active channel before you start painting. Now we have a grayscale mask that can be loaded as a selection for isolating the fireworks.
Click on RGB in the channel palettes to make all channels active and return to the color view of your image. Next from the Selection menu, choose Load Selection. In the dialog box, choose "Alpha 1" or "Red Copy" (depending on whether you are using an older or newer versions of Photoshop as noted above.
Here you can see the selection marquee surrounding the fireworks.
Next, invert the selection (Selection > Invert in older versions of Photoshop, or Select > Inverse in newer versions) and hit delete to remove the background. Make sure your image is on a layer before hitting delete. If the layer palette shows only one layer labeled background, you must promote it to a layer by double clicking on the background in the layers palette.
Here you can see the fireworks with another background dropped into the layer below. There's just one more step that we can do to improve this image.
From the layers menu choose matting, then Remove Black Matte.
As you can see below, removing the black matte makes a considerable improvement.
Any time you pull an image from its background, it's a good idea to try each of the three matting commands. Sometimes one will produce better results than another, and sometimes none of them appear to have any effect at all... it all depends on the combination of your foreground and background. But don't overlook them entirely because they can often make a world of difference.
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Some images from Nova Development's Art Explosion 600,000.