INTRODUCTION TO LAYERS - Replacing a background element.
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All images © by Jon Davison 2007.

Layers are what Photoshop is universally known for. The ability to separate and move
parts of an image or graphic elements freely without affecting the original image. You
can think of them in a similar way to clear acetate sheets with varying amounts of
content on each. The top one will eclipse the one beneath and so on. The similarity
though ends here, as with layers you can change their transparency, or opacity of
each one. You can move them up or down within the layer stack. You can link layers,
group them etc.


Original frame (click for a larger view)

Lets say you wish to replace the light grey background in the image (above), with
one that matches her skin colouring. Rather than using a colour control to change the
colour, we will replace the background as a layer. By default, when you open an image
in Photoshop, you will notice that it will be locked (below left), and entitled
‘Background’. This means that it is NOT a Layer, and you cannot erase it or cut the
image out without having a solid colour beneath it.





In order to use it as a layer you need to unlock it. Simply ‘double click’ the icon in
the Layer Palette. In the New Layer window that appears you can type a title for
the layer, then click ‘okay’ (above right). This action removes the lock icon and
turns it into a layer .

Left: Background unlocked. Right: Background erased

So the image is now a Layer, allowing us to erase, or cut parts of it out. In short, if
we want we can replace the background by removing the grey wall behind the subject.
The areas around the woman are now ‘transparent’. The grey and white checkerboard
background represents transparent areas with no pixel content, ie where it has been
erased, and is now the standard concept for all applications where transparency is
represented. You will see this pattern or background whenever pixels have been
removed from an image.

This means that if we place a second, solid colour (d09970)
Layer beneath the image of the woman like so …..


Click for larger view

…. it will be visible as it is now the background. It also means that if we erase
any part of the woman out, say her hair, or eyes etc, then the background will
be visible. Notice that the new colour is a solid fill in a new layer. As this new
layer sits beneath the woman, it is visible only because the wall content on her
layer has been erased.

(grateful thanks to Carina Hoang)