Perhaps it is because of the name, but the High Pass filter is often overlooked by photographers. It is impossible to know what it does by the name alone. Nevertheless, it is one of the most versatile filters in Photoshop because it can both sharpen and soften an image. Let’s see how to do both.
To sharpen an image, most photographers probably use the Unsharp Mask or Smart Sharpen filters. While these are great, the High Pass filter may be a bit easier to use.
Before sharpening an image, it is a good idea to duplicate it in the Layers palette. In that way, we don’t lose the pixel information in the original image. This comes in handy if we make mistakes or need to start over. One way to duplicate a layer is by clicking on the Background Layer and pressing CTRL+J on a PC, or CMD+J on a Mac. This creates a duplicate of the layer selected.
Once the layer is duplicated, go to Menu>Other>High Pass and select High Pass. This will gray out the layer and give you a dialogue box that allows you to adjust the amount of sharpening by sliding or adjusting the pixel radius.
The High Pass filter works by adjusting only the edges of an image. Photoshop senses edges by reading the difference in color between pixels next to each other. When you increase the radius, you expand the area Photoshop will use to sense pixel changes. A high radius will spread the sharpening over a broader area of the image and result in a distorted or extreme sharpening. In this case, I am using a 2.5 pixel radius. I don’t want to over sharpen it. This is an image that with a 300 pixel resolution. A higher resolution might require a higher radius and a lower one might need a lower radius. You may need to experiment before finding the one that works best.
Up to now, we have a very gray layer sitting on top of the original background layer. It is difficult to see how this can make any difference to the image since we can’t see anything, but be patient. We have one more thing to do. Go back to the Menu bar at the top of your screen and select Menu>Adjustments>Hue/Saturation. In the dialogue box, select the Saturation slider and move it to the left to make it zero. Lowering the saturation to zero is an optional adjustment, but doing it will often reduce the color fringing or the halo effect that can come with sharpening.
Once I complete this step, I will change the Blend mode of the High Pass layer to Overlay. This mode blends with the layer below and reveals the sharpening effect we just created. If I want more sharpening, I can change the blend mode to Hard Light. If I want less sharpening, I can use Soft Light. I can also reduce the layer’s opacity. I have quite a bit of control using this method.
The image below shows the difference between the original image and the new sharpened one. I think the High Pass filter allows the photographer a great deal of control over sharpening using an easy interactive approach.
On this image, I’m going to apply a softening to the model’s skin. This is a useful technique for portraits.
As with the first image, I duplicate the background layer using CTRL+J for PC or CMD+J for Mac. After duplicating the layer, I go to Menu>Other>High Pass and apply the filter it to the layer.
Because I want to soften the image, I will do the opposite of what I did to sharpen it. I will move the Radius Slider to the right increasing the area Photoshop will use to read the edges. In this case, I am using 15.0. You may need to experiment to find the right one.
After applying the High Pass filter to the layer, I will do a Select All by pressing CTRL+A for PC, or CMD+A for Mac. Then I will go to Menu>Adjustment>Invert. This will reverse everything and change the way the image looks.
Once I invert the image, I can change the layer blending mode. This time, I will use Soft Light. Once I do that, it becomes easy to see how the image got softer.
While this softens the skin, it also softens the entire image. To keep the effect only on the skin, I will create a Layer Mask. To do that, I click the Layer Mask button at the bottom of the Layer Palette.
Once I have the mask, I can select a brush. I generally use a brush with a feathered edge at 100 percent opacity. Because my mask is white (reveals all), I will use a black brush to hide those areas I want to appear sharp. In this case, I will brush over the model’s eyes, lips and hair. This will make the soft skin look more credible because other areas in her face are sharp.
After you complete this step, you can compare the softening with the original by turning off visibility in the High Pass layer. You can also view the difference below.
You can use this technique on any image you want to sharpen or soften. It works on portraits, still lifes, and landscapes. Have fun.
Photos by ahockley
Sharpen Photo: http://www.flickr.com/photos/ahockley/3674485992/