The advanced blending options in the Layer Styles window are extremely useful. We can specify which pixels of the active layer and of the underlying visible layers will be opaque based upon their brightness. This is a very powerful feature often neglected by Photoshop users. This Photoshop tutorial will explain you how to use these advanced settings.
Below you can download the two images you will use in this Photoshop tutorial:
Open the image FULLMOON.JPG. From the menu select Select>All
to select all pixels. Then select Edit>Copy
to copy them into your clipboard. Close this image.
Now open the image SUNSET.JPG. Select Edit>Paste
to paste the full moon image. Press V
to select the move tool and drag to position the moon layer above the tree branches, as shown in the image below.
We want to knock out the black background around the moon. We can use the elliptical marquee tool to create a circular selection around the moon, inverse it, feather it and delete it. But what can we do if we want the moon to appear behind the tree branches? Our task is getting tougher. Using a layer mask would be an option yet it would require a lot of work. Fortunately Photoshop offers us a powerful and flexible feature.
Select the Moon layer and double click its thumbnail to open the layer styles window. On the BLEND IF area you can see two horizontal bars. Underneath each one of these bars you can see a black slider and a white slider; each slider is divided into two parts.
Click the black slider underneath the first bar and move it to the right until you read the tonal value of 40 (see the image below).
The black background around the moon has disappeared:
How did this happen? By dragging the black slider to the right you 'told' Photoshop to make invisible all the active layer pixels that were darker than the value of 40. Similarly if you move the white slider to the left, you will make all the active layer pixels that are lighter than a specific value to disappear!
So far we learnt that the first bar provides advanced control over layers blending based upon the brightness of the pixels of the active layer. There are two more important things to learn. Back to work!
We want to make the moon appear behind the trees. In other words we want to bring forward the dark pixels of the underlying layer(s).
Drag the black slider of the second bar to the right until you read the tonal value of 20. This brings forward the pixels of the underlying layer that are darker than the tonal value of 20. As a result the dark tree branches and leaves appear in front of the bright moon pixels.
There is another important thing to learn. If you magnify the moon you will notice that the tree edges appear to be very jagged (see image below).
It’s time to find out why the sliders are divided into two parts. Hold down the Alt key (PC) or the Option key (Mac) and drag the second bar's black slider to the right. The slider splits into two parts. Drag to the right, until you read the value of 20 / 80 (see image below).
In this way you specify a tonal blending range within which the transition from visible to non-visible pixels takes place. As a result we create a soft blending effect. Now the tree edges look soft and the overall effect is natural:
and move the moon with your mouse!
By default any changes in the BLEND IF parameters affect all color channels. You can select an individual color channel instead of the grey channel in the BLEND IF dropdown menu and experiment further.