Blend If is very much an overlooked and even mysterious feature
to almost any Photoshop user. If you ever tried looking this feature
up in manuals and books, you may not have been able to find it. In
fact even searching Photoshop Help will not yield a title with Blend
If in it (though the feature is referenced by function in ‘Specify a blending mode for a layer or group’ and ‘Specify a tonal range for
blending layers‘). While the tool may not be a very popular target
for tutorials and documentation, it is an enormously powerful tool
that has been part of layers since the very beginning.
The Advanced Blending and Blend If sections of the Layer
Styles screen offer additional
layer advantages, not often explored by very powerful.
What Blend If can do is help you target changes and corrections
based on the color or tonal content of a layer. In a way it is like
an auto-mask, in that it will mask a layer without you having to
actually create a mask or a selection—and these masks can be
highly complicated without much work. It will target content of
a layer based on a set of sliders (the Blend If sliders on the Layer
Styles dialog), and those slider positions. Before we go any further,
let’s take a look at the basic functionality and how you control it
before we really try to look at what it can do.
- Open a new image 720 x 720 pixels with a white background, as shown below.
The suggested sample image should use the settings shown here.
- Create a new layer and call it Blend If Test.
- Press D to set the default colors (black and white).
- Choose the Gradient tool and be sure the Options are set to
Linear Gradient, Normal mode, 100% opacity, and uncheck
Reverse, Dither and Transparency.
- Click on the lower left of the image and drag the cursor to the
upper right, then release the mouse. The image should fill in a
gradient from black to white from the lower left to the upper
- Take a snapshot of the image by clicking the snapshot button
at the bottom of the History palette (Windows > History). Leave
the name as the default (Snapshot 1). This will make it easy to
return to the state of the image before blending is applied and
without having to open the Layer Styles dialog to reset.
- Double-click the Blend If Test layer in the layers palette
(anywhere but on the thumbnail or over the name). This will
open the Layer Styles dialog.
- Click on the black This Layer slider and drag it to the center of
the slider range at 128 as shown below.
As you drag the cursor, the image on screen
should appear to swipe from the lower left corner half way across
the image. Notice that the layer in the layers palette retains its content.
The numbers on the Blend If sliders are measured in
levels 0–255. This corresponds to black (0) to white (255) in a
grayscale gradient. The change in position of the slider limits the range of what is
visible in the layer (in this case the gradient) so it blends with what
is below based on those slider positions. Everything to the left
of the black slider and everything to the right of the white slider becomes transparent. If you shut off the visibility toggle for the
Background layer you can see the transparency. Continuing from
the exercise, try the following slider positions to get a better feel
for the way it works:
- Move the black This Layer slider back to 0 and then move the
white This Layer slider to 128.
The gradient between gray and white will become transparent
to see through to the background in the upper right of the image.
- Move the black This Layer slider to 192 and then move the white
This Layer slider to 63
The area between the white slider and the black slider become transparent
to see through to the background in the middle
of the gradient range.
Applying layers with Blend If can occasionally be
confounding when using the This Layer slider. Any changes
applied directly to the layer where the Blend If sliders are set
may result in unexpected changes in the image. To test this out,
make a Levels adjustment to the Blend If Test layer (Image > Adjustments > Levels). When the dialog opens, swing the center
gray slider left and right and watch how the image behaves.
Close the Levels dialog without committing the change. Now
do the same thing with an adjustment layer by choosing Levels
from the Create new Fill or Adjustment Layer menu on the
layers palette. This is one more clear case for using adjustment
layers instead of direct application of change.
The same concepts hold true for using the Underlying Layer
sliders. The main difference is that the content of the current
layer will blend based on the content of the layers below, rather
than the content of the layer where you apply the blend—layer
transparency still effects the current layer. To see the results of
using Underlying Layers, do the following:
- Click Snapshot 1 in the History palette to reset the image and
Blend If sliders.
- Double-click the Background layer and rename it to White Layer.
- Change the order of the layers in the layer stack by pressing
Command + ] / Ctrl + ].
- Double-click the White Layer in the layers palette to open the
Layer Styles dialog.
- Click on the black Underlying Layer slider and drag it to the
center of the slider range at 128.
The white layer becomes transparent over the brighter area
of the lower layer so you can see through it to the lighter half of the
- Move the black Underlying Layer slider to 192 and then move
the white Underlying Layer slider to 63.
The white layer becomes transparent over the mid-tone area of the
lower layer so you can see through it to the mid-tone ‘half’ of the
These examples are hard-edged application of Blend If in its
simplest form. Several other features of Blend If allow partial
blending and blending based on color ranges rather than just
tone. Partial transparency (the real ‘blending’ form of Blend If ) can
be created by splitting the sliders. Color targeting can be done by
choosing ranges for the Red, Green and Blue sliders found under
the Blend If drop list. Lets look at how to split sliders
to have all the basic functions in tow:
Blend If can be adjusted per channel so that
blending can be targeted to specific color
- Click Snapshot 1 in the History palette to reset the Blend If for
the layers and the layer order.
- Open the Layer Styles for the Blend If Test layer by doubleclicking
- Move the black This Layer slider so it is at 128.
- Hold down the Option/Alt key [Mac/PC] and click on the left of
the black slider and then drag it to 0. The slider will divide into
Holding the Option/Alt key allows you to split the slider,
be sure to click on the side of the slider that is on the side you will
be moving toward.
Splitting the slider will blend from 0% to 100% between the split
halves. Splitting the sliders allows you to make a softer transition
in blends, similar to blurring a mask or feathering a selection. The
idea is that you gain control over how blends dissipate, rather than
using them as an on/off switch for a particular range. As on/off
switches the edges might end up hard and blocky, but by
splitting the sliders you can offer better opportunity to control
So, what would you use Blend If for? Really, often for situations
that seem otherwise hopelessly complex. For example, say you
have taken a shot of a leafless tree in silhouette against a blue
sky and you think it might look better with some other sky, some
interesting clouds, or against a sunset, etc. It might seem to be
a daunting task to make a selection between all those branches.
You might try dabbling with the magic wand, but your results
will be pretty sketchy. Blend If offers the opportunity to make the
replacement without having to make a potentially unnerving
and complex mask or selection. You can use measurements from
your image to determine a range you want to replace, and then
apply appropriate Blend If settings you make directly from the
That makes it sound like a miracle cure to use Blend If… and there
are occasions where it will produce some amazing results with
little effort. On the other hand, getting to do what you want may
require combining it with masking or other techniques to achieve
a result—like any other tool it is best to think of it as a companion
to other functions rather than the lone ranger or some other hired