Localized Contrast in Photoshop -- Part III

Article and Photography by Ron Bigelow

www.ronbigelow.com

Photoshop CS4 Used in this Tutorial

The basic editing of the cactus flower image has been completed. However, there are a couple of problems that need to be addressed: color changes and clipping.

Color Changes

Anytime that contrast is edited in an image, there is the risk that some of the colors could change. With this image, the Contrast layer was added to boost the small scale contrast and a Curves layer was added to boost the large scale contrast. Each of these affects the contrast and can cause a color shift. Thus, it is necessary to ensure that USM and Curves are affecting only the luminosity of the image. This is really very easy.


Figure 1: Contrast Layer Luminosity Blend Mode

Starting with the Contrast layer, all that needs to be done is to change the Blend mode of the Contrast layer to Luminosity on the Layers panel (see Figure 1).

Figure 2: Curves Layer Luminosity Blend Mode
Next, the Blend mode of the Curves layer is similarly changed to Luminosity (see Figure 2).

Clipping

That was pretty simple. However, there is one more problem that needs to be addressed. The USM filter that was applied to enhance the small scale contrast can cause clipping of some tones. This is because the small scale contrast boost can push the very light tones from very light to white. Thus, the tones become clipped, and a loss of highlight detail results. Similarly, the contrast boost can push the very dark tones from very dark to black. The result is a clipping of the dark tones and a loss of shadow detail.

Since the USM filter modifies the Contrast layer, this problem is addressed by working on the Contrast layer. With the Contrast layer selected, the Add a layer style icon is clicked and Blending Options is chosen (see Figure 3).

Figure 3: Add a Layer Style

 

 

Figure 4: Layer Style Dialogue Box

The Layer Style dialogue box appears (see Figure 4). The Blend If controls that are found in the Advanced Blending section of the dialog box will be used to address the clipping issue.

The Blend If option determines how the pixels of a layer and the underlying layer blend together. The Blend If pop-up determines whether the Blend If adjustments will be based on the RGB channel, by selecting Gray, or one of the individual color channels. Since it is necessary to protect all the color channels from clipping, this should be set to Gray. The This Layer bar determines which pixels from the selected layer will blend. The Underlying Layer bar will not be needed for this edit, so it can be ignored.

 

Figure 5: Initial Black Slider Adjustment

At the left end of the This Layer bar is the Black slider (see Figure 5). Dragging this slider to the right prevents the darker pixels, from the layer on which we are working, from being blended with the layer below. By moving the Black slider to a value of fifteen, pixels in the Contrast layer with tonal values less than fifteen (i.e., with tones darker than fifteen) will not blend. Instead, the pixels from the underlying layer will show through. This prevents the darker tones from being clipped.

 

Figure 6: Initial White Slider Adjustment

At the right end of the This layer bar is the White slider (see Figure 6). Dragging this slider to the left prevents the lighter pixels, from the layer on which we are working, from being blended with the layer below. By moving the White slider to a value of 240, pixels in the Contrast layer with tonal values greater than 240 (i.e., with tones lighter than 240) will not blend. Instead, the pixels from the underlying layer will show through. This prevents the lighter tones from being clipped.

 

Figure 7: Final Slider Adjustments

However, this creates a bit of a problem. There is now a rather abrupt transition between the pixels in the Contrast 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 on a PC or the Option Key on a Mac and clicking on either the Black or White slider will split the slider into two sliders (see Figure 7). As you can see, there are now four sliders. For both the Black and White sliders, the inner halves of the sliders determine where the pixels in the Contrast Layer start to be eliminated from the blending and the outer halves of the sliders indicate where the blending has stopped completely. These sliders are now adjusted so that the abrupt transition is replaced with a gradual tapering off. Clicking OK closes the dialogue box. Any possible clipping of the shadows or highlights has been eliminated.

At the beginning of this article series, it was stated that it was necessary to create a separate layer for the small scale contrast editing instead of just adding the USM filter to the Cactus layer. The reason for this is now obvious. It is necessary to have both the original Cactus layer and the Contrast layer so that Blend If can be used to blend the two layers in such a way as to remove the clipping that may result from the use of USM.

Fine Tuning

Figure 8: Final Hue/Saturation Adjustment

A close examination of the image reveals that these last editing steps have resulted in a decrease in the image saturation. This is due to the Contrast and Curves layers' Blend modes being changed to Luminosity. To bring up the saturation to its original level, the saturation is increased a small amount on the Hue/Saturation adjustment layer (see Figure 8)

Figure 9: Final Contrast Adjustment
In addition, the contrast is increased a small amount by adjusting the Curves layer (see Figure 9).
Figure 10: Layers Panel
Finally, the image is sharpened by adding a sharpening layer (the sharpening procedure is beyond the scope of this article, so the sharpening steps will not be shown). The Layers panel now looks as shown in Figure 10.

Final Image

So, how does the final image look? Check out Figure 11. To compare the final image to the original image, just move the mouse over the image, and the original image will appear.

Figure 11: Final Image

Camera Raw

Part IV of this series will look at adjusting localized contrast in Camera Raw.

Articles

Localized Contrast -- Part II     Localized Contrast -- Part IV