Beginner's guides to digital SLR Photography

A sneaky way to cut complicated objects out of their background.

See that tree in the photo below? It took me only two minutes to mask it (deep-etch it) and put some alternative background beneath it. How is that possible? By using Adobe Photoshop’s channels. Yeah sure, at first glance this tutorial makes it look anything but speedy. But that’s only because I spend some time explaining things.

deep-etched tree

One tree, two backgrounds. To cut this tree out of its background manually would drive you nutty and take many boring hours.

Blue-faced Honeyeater

Imagine you want to cut this Blue-faced Honeyeater and the plant out of the blue sky background. Maybe someone is telling you it has to go onto a different kind of sky. This involves a process which is sometimes called masking or deep-etching, and doing it the way most people do their deep etches would take at least 20 minutes with an image like this one in high resolution. And it would be a boring job too — yep, let’s not forget boring.

Using channels, you can get it done in a couple of minutes.

Photoshop’s way

Earlier versions of Photoshop had a tool called ‘Extract’ which was great at doing tasks like this. Then they removed it and put in a new system which uses the edge-select tool. I never really figured that new method out although I’m sure it’s a great method. Instead, I use other, much simpler ways. And when the shape is madly complicated I use the method described below.

But first, here’s how it works

It’s easier to learn if you understand how it works.

a ball and the shape of its mask a ball and the shape of its mask

Imagine you wanted to deep-etch a ball like the one in the picture 1. In other words, you want to cut it out of its background. The ball is round, and so you’d make a round (ball-shaped) selection around it, like the silhouette in picture 2.

bird-shaped mask bird-shaped mask

Likewise, if you want to deep-etch a bird on a complicated branch then you’d want to make a bird-on-a-complicated-branch-shaped selection.

The fastest way of making a shape that looks like that is to use the photo itself to draw that shape.

The ideal picture

I’ve chosen a picture with a nice flat background because it makes this process easier to do. Which makes it easier to learn.

It’s got just enough detail to make the manual method of working look like a bit of a pain.

If you want, you can practise on the same file I used. I’ve made it available to download here.

Channels are your friend

No, really. They are. Most people avoid channels. They see them as being kind of nerdy. And those same people spend all day hunched in front of a computer deep-etching something like the tree photo above, when I did it in less than 2 minutes. Who’s nerdy now?

So with your image opened in Photoshop, go to the Channels palette.

Step 1: Choose the best channel

channels

If the photo is an RGB picture like the one I’m using then you’ll see three channels. One for Red (R), one for Green (G) and one for Blue (B). And at the top of the palette you’ll notice an RGB channel, which is a combination of the three.

Click on one at a time and you’ll see how each of those channels look.

What you’re hunting for now is the channel that looks closest to a black-and-white version (a silhouette) to define the shape of the bird on the complicated branch.

channels

I’ve clicked on the Red channel. Doesn’t look enough like a silhouette to me.

The Green and Blue channels weren’t a whole lot better.

So the RGB channels were a bit of a disappointment in this case.

Normally one of those channels would have been pretty good. But you don’t have to limit yourself to just the R, G and B options.

If you convert your image to a CMYK document (go to the Image menu at the top of your screen and select Mode > CMYK Color), then you’ll see you’ve now got 4 channels: C, M, Y and K.

channels

This time, you’ve got some much better options. I especially like the look of the Yellow channel in this example. Because if you squint your eyes a bit it almost likes the perfect silhouette already! So in this instance, you’ll be choosing your Yellow channel.

Step 2: Duplicate the channel

channels

So because that’s the best channel for the job, you duplicate it. Click on the tiny down-arrow menu icon in the top-right corner of the palette and choose Duplicate Channel …

You can leave the name of the new channel as ‘Yellow copy’ and click ‘OK’.

channels

Woohoo! You’ve got a new channel called ‘Yellow copy’.

Step 3: Turn your new channel into a silhouette

With ‘Yellow copy’ selected, we’re now going to change its appearance.

Go to the Image menu at the top of your screen and select Adjustments > Curves …

Curves Curves

Picture 1 shows how the Curves palette looks when you start. Drag the top right of the line to the left until the background goes totally white. And drag the bottom of the line to the right until most of the bird goes totally black. Like how it is in Picture 2.

After applying the curves

And shown here is how your duplicated channel is looking now. It’s almost a silhouette. You just need to manually paint in those few remaining grey bits on the bird using the brush tool.

After applying the curves

So select the Brush tool, load it with black, and paint in those last few blobs and speckles of grey until the whole shape is properly black.

You’ve got your silhouette. But how do you change that into a deep-etch? Well, that bit is easy now. Because channels make it easy.

Step 4: Make a selection

channels

First of all, in your Channels palette, click on CMYK to restore the image to full colour, like I did (above).

Load selection dialogue box

Then go to the Select menu at the top of your screen and choose Load Selection …

Make sure that the duplicated channel is the one chosen in the pop-up menu. In this case it is the one called ‘Yellow copy’. That was the one you did all that work on.

With ‘New selection’ chosen for the Operation, click ‘OK’.

You’ve now got a bunch of marching ants (a selection) around the bird and the complicated branch.

Or have you?

If you have a better look at your marching ants you’ll see that they’re actually tracing around the shapes of the blue-sky bits, instead of the bird-on-branch-bits. In other words, we’ve selected the inverse of what we want.

Load selection dialogue box

I could have avoided this by checking the ‘Invert’ option in the previous step but usually I forget. But no worries, when we get the reverse of what we want then we can simply reverse our selection by doing Command + Shift + I (or Control + Shift + I if you use a PC). Of if you prefer to use the menus it’s the Select menu at the top of the screen and choose Inverse.

Now we have our marching ants tracing around the bird and the branch.

Step 5: Separate the object from its background

Go to your layers palette and make sure that the Background layer is selected. Then do Command + J (Control + J if you use a PC). Or if you want to use the menus, go to the Layer menu at the top of the screen and choose New > Layer via Copy

deep-etched bird and branch

Done! If you go to your layers palette (above) and click on the little eye symbol next to the Background layer (to hide the background) you’ll see that the bird and its branch have been copied into their own layer.

Now you can drag a new background into a layer behind the bird.

Better choice

I’ve put in some out-of-focus foliage behind the bird but anything else can go in there.

You might want to now revert your photo back into RGB mode.

A few more points.

Channels are able to capture the very fine details

And finally, for the folks who have a good understanding of Photoshop layers.

Photography

Beginners’ guides to digital SLR photography

primer

Before you start

Basics

The essential basics

Basics

Making sense of technical stuff

Photography words

Photography words explained

frog

Sneaky stuff

Colours

Common problems and their solutions

Preying mantis

Taking things further

Moon

Photography at night

Other photography stuff

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