Blending Layers in Photoshop with Blend IF

Article and Photography by Ron Bigelow

www.ronbigelow.com

Photoshop CS or Photoshop CS2 Used in this Tutorial

Tools such as Levels, Curves, and Hue/Saturation provide powerful image editing capabilities. When used in conjunction with layers, they become even more powerful. However, these tools are not perfect. One issue that occurs with these tools is that, by themselves, these tools are applied in a global manner. In other words, they are applied to the entire image. However, sometimes it is not desirable to apply the tools globally. It may be desired to apply a tool to only a portion of the image. Often, it is desired to apply a tool to only a specific tonal region of the image. For instance, an image may require additional contrast in the highlights but not the mid-tones or shadows. Various tools and techniques exist that allow these tools to be restricted to specific areas of an image (e.g., masks and the Gradient tool). However, one of the easiest is often overlooked: the Blend-If option in the Layer Style dialogue box.

The Blend If Option

Figure 1: Layer Style Dialog Box

The Blend If option determines how the tonal regions of a layer and the underlying layer blend together. The Blend If option is accessed by choosing Layer/Layer Style/Blending Options. The Layer Style dialog box appears as shown in Figure 1. The Blend If controls are found in the Advanced Blending section of the dialog box.

The Blend If pop-up can be found at the top of the Blend If section of the dialog box. This allows the photographer to choose whether Blend If adjustments will be based on the RGB channel (i.e., Gray) or one of the three, individual, color channels. Generally, the Gray option is chosen. The This Layer bar determines which pixels from the selected layer will blend. The Underlying Layer bar determines which pixels from the underlying layer will blend.

Figure 2: This Layer Adjustment
Figure 2 demonstrates how the This Layer bar works. At the left end of the bar is the Black slider. Dragging this slider to the right prevents the darker tones from the active layer from being blended (the active layer is what the dialog box refers to as "This Layer"). In this case, pixels in the active layer with tonal values less than thirty-one (i.e., darker) will not blend. Instead, the pixels from the underlying layer will show through. At the right end of the Layer bar is the White slider. Dragging this slider to the left prevents the lighter tones from the active layer from being blended. In this case, pixels in the active layer with tonal values greater than 229 (i.e., lighter) will not blend. Again, the pixels from the underlying layer will show through. Thus, pixels from the active layer with tonal values from thirty-one to 229 will blend. The other pixels from the active layer will not blend.
Figure 3: This Layer Adjustment with Sliders Split

However, this creates a bit of a problem. There is now a rather abrupt transition between the pixels in the Active Layer that will blend and those that will not. This will, likely, result in rather harsh transitions between these tonal regions. Luckily, a simple solution exists. Holding down the Alt key (Option Key for a Mac) and clicking on either the Black or White sliders will split the slider into two sliders. As seen in Figure 3, there are now four sliders. For both the Black and White sliders, the inner halves of the sliders determine where the pixels in the Active Layer start to be eliminated from the blending and the outer halves of the sliders indicate where the blending has stopped completely. Figure 3 provides an example. In this image, at the shadow end of the bar, the Active Layer pixels start to be eliminated from the blending at a tonal value of thirty-four and are completely eliminated at a tonal value of twelve. Similarly, at the highlight end of the bar, the Active Layer pixels start to be eliminated from the blending at a tonal value of 221 and are completely eliminated at a tonal value of 241.

The abrupt transition between the pixels in the Active Layer that are blended and those that are not has been eliminated. At the same time, a greater amount of control over the blending has been achieved.

Figure 4: Underlying Layer Adjustment
Figure 4 demonstrates how the Underlying Layer bar works. At the left end of the bar is the Black slider. Dragging this slider to the right prevents the darker tones from the Underlying Layer from being blended. Instead, the darker pixels show through the active layer. In this case, pixels in the Underlying Layer with tonal values less than twenty-two (i.e., darker) will show through the active layer. At the right end of the Layer bar is the White slider. Dragging this slider to the left prevents the lighter tones from the Underlying Layer from being blended. Instead, the lighter pixels show through the active layer. For this dialog box, pixels in the Underlying Layer with tonal values greater than 230 (i.e., lighter) will show through the active layer. Thus, pixels from the Underlying Layer with tonal values less than twenty-two and pixels with tonal values greater than 230 will show through the active layer. The other pixels from the Underlying Layer will blend.
Figure 5: Underlying Layer Adjustment with Sliders Split
It probably comes as no surprise that the issue with the abrupt transition between the pixels that will blend and those that will not blend may become a problem if the settings used in Figure 4 are employed. Splitting the sliders, in the same manner as before, solves the problem. Figure 5 shows the four Underlying Layer sliders after the sliders have been split. For both the Black and White sliders, the inner halves of the sliders determine where the pixels in the Underlying Layer start to be eliminated from the blending and the outer halves of the sliders indicate where the blending has stopped completely. As shown in Figure 5, at the shadow end of the bar, the Underlying Layer pixels start to be eliminated from the blending at a tonal value of thirty-six and are completely eliminated at a tonal value of twelve. On the other end of the bar, the Underlying Layer pixels start to be eliminated from the blending at a tonal value of 221 and are completely eliminated at a tonal value of 246.

Example: This Layer Blend If Adjustment

Figure 6: Image with a Levels Adjustment

Probably, the best way to understand the Blend If option is to see a couple of examples of its use. Figure 6 shows an image that utilized a Levels adjustment to increase the contrast of the image. The Layers Palette for this image is shown in Figure 7.

Figure 7: Layers Palette with Levels Layer
Figure 8: Shadow Area with Little Detail
In general, the contrast is as desired, except in the darkest shadows. Figure 8 shows a crop of one of the shadow areas. This crop shows that this shadow area has almost no detail. What is desired is to have the Levels adjustment apply to the image -- except the darkest shadows. This can be done with the Blend If option.
Figure 9: Layer Style Dialog Box

With the Levels layer selected, Layer Style is launched, and the Blend If option accessed. Since it is desired to prevent the Levels adjustment from affecting the darker pixels, the Black This Layer slider is split and moved to the right as shown in Figure 9. This Blend If adjustment starts to phase out the effect of the Levels adjustment at pixels with a tonal value of twenty-one and has completely eliminated the effect at a tonal value of 5.

Figures 10 and 11 show the crops before and after the Blend If adjustments. As can clearly be seen, the Blend If adjustment had brought out some of the shadow detail.

Figure 10: Crop without Blend If Adjustment
Figure 11: Crop with Blend If Adjustment

Example: Underlying Layer Blend If Adjustment

In the first example, the editing was done using the This Layer adjustments. In the following example, the editing is done using the Underlying Layer adjustments.

Figure 12 shows a pattern that might be used for some graphics work. However, the pattern is black and white. It is desired to have a black and red pattern using the red shown in Figure 13. Now, a mask could be created that would blend the two images. However, a much simpler solution can be created by combining the pattern and the color through the use of the Blend If option.

Figure 12: Pattern
Figure 13: Solid Color
Figure 14: Layers Palette
Two layers are created in the Layers Palette. The bottom layer (Layer 1) has the grid pattern, and the upper layer (Layer 2) is filled with solid red.
Figure 15: Layer Style Dialog Box
With Layer 2 selected, Layer Style is launched, and the Blend If option accessed. Figure 15 shows the Layer Style dialog box. The Black Underlying Layer Slider is moved to the right. For this image, the slider does not need to be split since the transitions from red to black in the final image are fairly abrupt. Therefore, it is not necessary to smooth out the transitions. A setting of around 26 will create the final image seen in Figure 16.
Figure 16: Final Image

The Blend If Option and Sharpening

One of the most valuable uses for the Blend If option is in sharpening. We all want sharp images. However, in the process of sharpening images, we do not want to sharpen the noise. The Blend If option can help resolve this issue.

With respect to sharpening and noise, the problem is the shadow areas. The shadow areas contain the most noise and the least amount of detail. Therefore, less sharpening should be performed in the shadows compared to the rest of the image. The Blend If option is perfect for this situation. To resolve the problem, a sharpening layer can be created and the Blend If option used to reduce, or completely eliminate, the sharpening in the shadows. For an explanation of this technique see the topic: Sharpening and Fine Tuning in my series on sharpening.

Summary

Sometimes, good things come in small packages. This is the case with the Blend If option. It is very simple to learn and simple to use. So much so that, sometimes, photographers tend to ignore it, preferring its more sophisticated looking cousins (e.g., Curves and masks). However, sometimes the most elegant solution is the most simple. For those cases, the Blend If option may just fit-the-bill.

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