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Blurring an Image

The commands under the Filter Blur submenu produce the opposite effects of their counterparts under the Filter Sharpen submenu. Rather than enhancing the amount of contrast between neighboring pixels, the Blur filters diminish contrast to create softening effects.

Applying the Gaussian Blur filter

The preeminent Blur filter, Gaussian Blur, blends a specified number of pixels incrementally, following the bell-shaped Gaussian distribution curve I touched on earlier. When you choose Filter Blur Gaussian Blur, Photoshop produces a single Radius option box, in which you can enter any value from 0.1 to 250.0. (Beginning to sound familiar?) As demonstrated in Figure 10-19, Radius values of 1.0 and smaller blur an image slightly; moderate values, between 1.0 and 5.0, turn an image into a rude approximation of life without my glasses on; and higher values blur the image beyond recognition.

Figure 10-19: The results of blurring an image with the Gaussian Blur filter using nine different Radius values, ranging from slightly out of focus to Bad Day at the Ophthalmologist’s Office.

Moderate to high Radius values can be especially useful for creating that hugely amusing Star Trek Iridescent Female effect. (This is the old Star Trek, of course.) Captain Kirk meets some bewitching ambassador or scientist who has just beamed on board. He takes her hand in sincere welcome as he gives out with a lecherous grin and explains how truly honored he is to have such a renowned guest in his transporter room, and so charming to boot. Then we see it — the close-up of the fetching actress shrouded in a kind of gleaming halo that prevents us from discerning if her lips are chapped or perhaps she’s hiding an old acne scar, because some cockeyed cinematographer smeared Vaseline all over the camera lens. I mean, what wouldn’t you give to be able to recreate this effect in Photoshop?

Color Plate 10-2 show a suitably comely lass — for the sake of this example, we’ll assume she has her pointy ears tucked up into her hat, and some intergalactic beautician has tweezed her eyebrows into a more humanoid shape. The following steps explain how to give her that glorious Kirk-O-Vision glow.

Figure 10-20: After applying Gaussian Blur (top left), I used the Fade command to lower the Opacity to 65 percent (top right) and to apply the Darken mode with 100-percent Opacity (bottom left). Overlaying another application of Gaussian Blur with Opacity at 80 percent and Linear Dodge mode in force created the final example in the figure.

STEPS: The Captain Kirk Myopia Effect

Select a portion of the image if desired. If you want to apply the effect to only a portion of the image, feather the selection with a Radius in the neighborhood of 5 to 8 pixels.

Choose Filter Blur Gaussian Blur. Enter some unusually large value in the Radius option box — say, 8.0 — and press Enter or Return. The results are shown in the first example of Color Plate 10-2 because the pixel dimensions of that image are about twice those of the black-and-white example.

Press Ctrl+Shift+F (z -Shift-F on the Mac) to bring up the Fade dialog box.To achieve the effect shown in the second example of Figure 10-20, I reduced the Opacity value to 65 percent, making the blurred image slightly translucent. This way, you can see the hard edges of the original image through the filtered one.

You can achieve additional effects by selecting options from the Mode pop-up menu. For example, I created the third example in Color Plate 10-2) by raising the Opacity back up to 100 percent and selecting the Darken mode option, which uses the colors in the filtered image to darken the original. I built upon this effect by pressing Ctrl+F (z -F on the Mac) to reapply my Gaussian Blur settings, pressing Ctrl+Shift+F (z -Shift-F on the Mac) to bring back the Fade command, lowering the Opacity to 80 percent, and choosing the Linear Dodge mode, as seen in the last example of Color Plate 10-2 shows this in color.

You know, though, as I look at this woman, I’m beginning to have my doubts about her and Captain Kirk. I mean, she has Scotty written all over her.

The preset blurring filters

Neither of the two preset commands in the Filter Blur submenu, Blur and Blur More, can distribute its blurring effect over a bell-shaped Gaussian curve. For that reason, these two commands are less functional than the Gaussian Blur filter. However, just so you know where they stand in the grand Photoshop focusing scheme, Figure 10-21 shows the effect of each preset command and the nearly equivalent effect created with the Gaussian Blur filter.

Figure 10-21: The effects of the two preset blurring filters (top row) compared with their Gaussian Blur equivalents (bottom row), which are labeled according to Radius values.

Antialiasing an image

If you have a particularly jagged image, such as a 256-color GIF file, there’s a better way to soften the rough edges than applying the Gaussian Blur filter. The best solution is to antialias the image. How? After all, Photoshop doesn’t offer an Antialias filter. Well, think about it. Back in the “Softening selection outlines” section of Chapter 8, I described how Photoshop antialiases a brushstroke or selection outline at twice its normal size and then reduces it by 50 percent and applies bicubic interpolation. You can do the same thing with an image.

Choose Image Image Size and enlarge the image to 200 percent of its present size. Make sure that the Resample Image check box is turned on and set to Bicubic. (You can also experiment with Bilinear for a slightly different effect but don’t use Nearest Neighbor.) Next, turn right around and choose Image Image Size again, but this time shrink the image by 50 percent.

Figure 10-22 shows an odd doodle I did in a fit of torpor. The top-left example in Figure 10-23 shows an enlarged detail from my masterpiece badly in need of some smoothing. To the right is a detail from the same image subject to Gaussian Blur with a very low Radius value of 0.5. Rather than appearing softened, the result is just plain fuzzy.

Figure 10-22: A doodle by yours truly. Read into it what you will.

However, if I instead enlarge and reduce the image with the Image Size command, I achieve a true softening effect, as shown in the lower-left example in the figure, commensurate with Photoshop’s antialiasing options. Even after enlarging and reducing the image four times in a row — as in the bottom-right example — I don’t make the image blurry; I simply make it softer.

Directional blurring

In addition to its everyday blurring functions, Photoshop provides two directional blurring filters, Motion Blur and Radial Blur. Instead of blurring pixels in feathered clusters like the Gaussian Blur filter, the Motion Blur filter blurs pixels in straight lines over a specified distance. The Radial Blur filter blurs pixels in varying degrees depending on their distance from the center of the blur. The following pages explain both filters in detail.

Figure 10-23: A detail from Figure 10-22 (top left) followed by the image blurred using a filter (top right). By enlarging and reducing the image one or more times (bottom left and right), I soften the pixels without making them appear blurry. The enlarged details show each operation’s effect on the individual pixels.

Motion blurring

The Motion Blur filter makes an image appear as if either the image or the camera was moving when you shot the photo. When you choose Filter Blur Motion Blur, Photoshop displays the dialog box shown in Figure 10-24. You enter the angle of movement in the Angle option box. Alternatively, you can indicate the angle by dragging the straight line inside the circle to the right of the Angle option, as shown in the figure. (Notice that the arrow cursor actually appears outside the circle. After you begin dragging on the line, you can move the cursor anywhere you want and still affect the angle.)

Figure 10-24: Drag the line inside the circle to change the angle of the blur.

You then enter the distance of the movement in the Distance option box. Photoshop permits any value between 1 and 999 pixels. The filter distributes the effect of the blur over the course of the Distance value, as illustrated by the examples in Figure 10-25.

Figure 10-25: A single black rectangle followed by five different applications of the Motion Blur filter. Only the Distance value varied, as labeled. A 0-degree Angle value was used in all five examples.

Using the Wind filter

The problem with the Motion Blur filter is that it blurs pixels in two directions. If you want to distribute pixels in one absolute direction or the other, try the Wind filter, which you can use either on its own or with Motion Blur.

When you choose Filter Stylize Wind, Photoshop displays the Wind dialog box shown in Figure 10-26. You can select from three methods and two directions to distribute the selected pixels. Figure 10-27 compares the effect of the Motion Blur filter to each of the three methods offered by the Wind filter. Notice that the Wind filter does not blur pixels. Rather, it evaluates a selection in 1-pixel-tall horizontal strips and offsets the strips randomly inside the image.

Figure 10-26: Use the Wind filter to randomly distribute a selection in 1-pixel horizontal strips in one of two directions.

Figure 10-27: The difference between the effects of the Motion Blur filter (top) and the Wind filter (other three). In each case, I selected From the Right from the Direction radio buttons.

To get the best results, try combining the Motion Blur and Wind filters with a blending mode. For example, as shown in Chapter 12.)

Figure 10-28: Combining the Wind filter (top) with Motion Blur (second image), the Lighten blend mode (third image), and a layer mask (bottom).

The result is a perfect blend between two worlds. The motion effect at the bottom of Figure 10-28 doesn’t obliterate the image detail, as the Wind filter does in Figure 10-27. And thanks to the layer mask, the motion appears to run in a single direction — to the left — something you can’t accomplish using Motion Blur onits own.

Radial blurring

Choosing Filter Blur Radial Blur displays the Radial Blur dialog box shown in Figure 10-29. The dialog box offers two Blur Method options: Spin and Zoom.

Figure 10-29: Drag inside the Blur Center grid to change the point about which the Radial Blur filter spins or zooms the image.

If you select Spin, the image appears to be rotating about a central point. You specify that point by dragging in the grid inside the Blur Center box (as demonstrated in the figure). If you select Zoom, the image appears to rush away from you, as if you were zooming the camera while shooting the photograph. Again, you specify the central point of the Zoom by dragging in the Blur Center box. Figure 10-30 features examples of both settings.

Figure 10-30: Five examples of the Radial Blur filter set to both Spin and Zoom, subject to different Quality settings. I specified Amount values of 10 pixels for the Spin examples and 30 for the Zooms. Each effect is centered about the bridge of the woman’s nose.

After selecting a Blur Method option, you can enter any value between 1 and 100 in the Amount option box to specify the maximum distance over which the filter blurs pixels. (You can enter a value of 0, but doing so merely causes the filter to waste time without producing an effect.) Pixels farthest away from the center point move the most; pixels close to the center point barely move at all. Keep in mind that large values take more time to apply than small values. The Radial Blur filter, incidentally, qualifies as one of Photoshop’s most time-consuming operations.

Select a Quality option to specify your favorite compromise between time and quality. The Good and Best Quality options ensure smooth results by respectively applying bilinear and bicubic interpolation (as explained in the “General preferences” section of Chapter 2). However, they also prolong the amount of time the filter spends calculating pixels in your image.

The Draft option diffuses an image, which leaves a trail of loose and randomized pixels but takes less time to complete. I used the Draft setting to create the top- right and bottom-left images in Figure 10-30. I selected the Good option to create the middle-left image and the Best option to create the middle and bottom images on the right.

Blurring with a threshold

The purpose of Filter Blur Smart Blur is to blur the low-contrast portions of an image while retaining the edges. This way, you can downplay photo grain, blemishes, and artifacts without harming the real edges in the image. (If you’re familiar with Filter Pixelate Facet, it may help to know that Smart Blur is essentially a customizable version of that filter.)

The two key options in the Smart Blur dialog box (see Figure 10-31) are the Radius and Threshold slider bars. As with all Radius options, this one expands the number of pixels calculated at a time as you increase the value. Meanwhile, the Threshold value works just like the one in the Unsharp Mask dialog box, specifying how different two neighboring pixels must be to be considered an edge.

Figure 10-31: The Smart Blur filter lets you blur the low-contrast areas of an image without harming the edges.

But the Threshold value has a peculiar and unexpected effect on the Radius. The Radius value actually produces more subtle effects if you raise the value beyond the Threshold. For example, take a look at Figure 10-32. Here we have a grid of images subject to different Radius and Threshold values. (The first value below each image is the Radius.) In the top row of the figure, the 5.0 Radius produces a more pronounced effect than its 20.0 and 60.0 cousins. This is because 5.0 is less than the 10.0 Threshold, while 20.0 and 60.0 are more.

Figure 10-32: Combinations of different Radius (first number) and Threshold (second) values. Notice that the most dramatic effects occur when the Radius is equal to about half the Threshold.

The Quality settings control the smoothness of the edges. The High setting takes more time than Medium and Low, but it looks smoother as well. (I set the value to High to create all the effects in Figure 10-32.) The two additional Mode options enable you to trace the edges defined by the Threshold value with white lines. Overlay Edge shows image and lines, and Edge Only shows just the traced lines. About the only practical purpose for these options is to monitor the precise effect of the Threshold setting in the preview box. Otherwise, the Edge options are clearly relegated to special effects.

Frankly, I’m not convinced that Smart Blur is quite ready for prime time. You already know what I think of the Threshold option, and it hasn’t become better here. Without control over the transitions between focused and unfocused areas, things are going to look pretty strange.

Figure 10-33 shows how the masking technique compares with Smart Blur. In the first image, I applied Unsharp Mask with a Threshold of 20. Then I turned around and applied Smart Blur with a Radius of 2.0 and a Threshold of 20.0, matching the Unsharp Mask value. The result makes the venerable Frederick Douglass look like he just sneezed while peppering his food.

Figure 10-33: The difference between relying on Photoshop’s automated Threshold capabilities (left) and sharpening and blurring with the aid of an edge mask (right). A little manual labor (even if it’s performed on the computer) still wins out over total automation.

In the second image, I created an edge mask — as explained in the “Creating and Using an Edge Mask” steps — and applied Unsharp Mask with a Threshold of 0. Then I pressed Ctrl+Shift+I (z -Shift-I on the Mac) to reverse the selection and applied Gaussian Blur with a Radius of 2.0. The result is a smooth image with sharp edges; Figure 10-34 shows a closer look.

Figure 10-34: A closer look at the “Smart Blur versus Edge Mask” debate.

Using the Lens Blur filter

Choose Filter Blur Lens Blur to bring up the large Lens Blur dialog box, shown in Figure 10-35. On the left side of the dialog box is the image preview, which is scaled to fit entirely inside the dialog box by default. If you want to adjust the zoom ratio, use the plus and minus signs in the lower-left corner or click the right-pointing arrowhead and choose an option from the resulting pop-up menu. As usual, you can hold down the spacebar and drag over your image to position it within the preview area. Next to the zoom options is the progress bar, which lets you know that Photoshop is still working hard during some of the slower, more complex Lens Blur calculations. The right side of the bulky Lens Blur dialog box contains the following options:

Figure 10-35: Bring your ideas into focus with the smart new Lens Blur filter. Focus? Blur? It works on so many levels!

Preview: When the Preview check box is turned on, the Lens Blur filter automatically updates the image preview every time you make an adjustment. For minute tweaking, this can be great, but sometimes this calculation-intense filter can take a while to give you a result, in which case you may want to turn off the Preview option. Even better is the ability to choose between Faster and More Accurate previews. Generally, it’s a safe bet to leave this set to Faster. Remember, these radio buttons are only for previewing. As soon as you click OK, Photoshop renders the best possible result it can.

Depth Map: Here’s where the wonders of the Lens Blur filter really shine. The Depth Map you specify contains information that assigns an imaginary position in space to every individual pixel in your image. By default, the Source pop-up menu offers three options: None, which performs blurring on each pixel in your image uniformly; Transparency, which determines what gets blurred in an image based on the transparency values of the pixels; and Layer Mask, which bases blur levels on the grayscale values in an image’s layer mask. Under the default settings, the black areas of the mask are treated as though they are in the foreground and the white areas are treated as though they are in the background, though you can reverse this by clicking the Invert check box or by adjusting these settings manually, as I’ll show you in a moment. If you’ve added an alpha channel to your layer, it too is available to choose as a depth map from the Source pop-up menu.

In Figure 10-36, I took an image of a hip young urbanite, added an alpha channel, and carefully created a depth map using the magnetic lasso and gradient tools. Next, I chose Filter Blur Lens Blur, selected the new alpha channel from the Source pop-up menu, and watched as the background sprung into sharp focus and our hair-dyed hero sunk into softitude. The problem, as you can see in the middle image in Figure 10-36, is that I reversed my values when I first created the depth map — I colored my desired foreground white and background black. Although I could exit the dialog box and perform an invert operation on the channel in question, the Lens Blur filter provides the Invert check box for a quick, easy fix. But Lens Blur goes a step further, allowing you to reassign the grayscale values to different levels of depth directly in the dialog box, no matter how you’ve created your depth map.

Figure 10-36: The extreme perspective of this image (left) is nice but I decided that a more shallow depth-of-field would lend our subject the “In Your Face!” feeling I was after. I created an alpha channel for use as a depth map (center). Then I applied the Lens Blur filter, clicked on our hero’s face to set the Blur Focal Distance, and blurred the other pixels at a Radius value of 33 (right).

Adjust the setting of the Blur Focal Distance slider to change which color in the depth map represents the in-focus plane of the image. In real-world terms, adjusting this value sets the focal plane of the image, or the distance from your camera in imaginary space that remains entirely focused. Any areas designated as either in front of or behind the focal plane will become out-of-focus. A value of 0 brings the pure black pixels into focus, a value of 255 brings the pure white pixels into focus, and any setting in-between sets a different level of gray as in focus. The Lens Blur filter provides an even quicker, more precise way to designate any portion of a layer as being in focus, however. Simply click any pixel in the preview image and watch as the Blur Focal Distance slider snaps to the pixel’s corresponding grayscale level in your depth map. If Invert is selected, clicking a portion of the image will set it as out of focus. For the image of my bespectacled chum here, all I needed to do was click once on his face to set it in focus and deem the rest of the image a distant, blurry memory.

Iris: The characteristics of genuine lens blur in a photograph can depend a lot on the shape of the iris in the camera lens that captured the photo. (An iris is a diaphragm comprised of plates that expand and contract to determine the amount of light entering the lens.) Photoshop’s Lens Blur filter gives you a number of options for simulating many different types of irises. From the Shape pop-up menu you can select anything from a triangular iris to an octagonal one. Experiment with the various Shape options together with the Blade Curvature and Rotation settings to create different types of realistic details and imperfections in your lens blur effects. As the number of sides in the iris increases, along with the Blade Curvature, the blur highlights will become more and more smooth until they are virtually circular.

The Radius setting is where you adjust the amount of blur applied to your image. You can think of it as the Photoshop counterpart to a camera’s f-stop (which regulates depth-of-field in real life), though the fact that Photoshop doesn’t know the focal length of the lens that captured the image prevents you from getting a direct, mathematical correlation.

Specular Highlights: When you blur an image through one of the other blurring filters in Photoshop, colors can get averaged and bright whites can become shades of grey. Photographers are well aware of the fact that no matter how much a photo is optically blurred, whites remain bright white. The Lens Blur filter accounts for this with the Specular Highlights section of the dialog box. Decrease the Threshold amount to add areas that will be affected by the highlights and increase the Brightness level to blast the image with pools of white. In addition to being optically accurate, Specular Highlights can also add a nice, otherworldly quality to an image.

Noise: When you apply a drastic blur to sections of an image, it tends to smooth out detail and color values. But as we’ve seen, the name of Lens Blur’s game is realism, and no matter how blurry a photograph is, it would look unnatural to lose film’s inherent grain detail. Thankfully, the Noise options can help artificially pull this detail back in. Adjust the Amount slider until the noise in the blurred section matches the original photo’s noise in the in-focus section. Below the slider, select either Uniform or Gaussian to set the type of noise (for my money, Gaussian is the way to go). Finally, you can make sure the noise you generate won’t affect the color in your image by clicking the Monochromatic check box.

Softening a selection outline

Gaussian Blur and other Blur filters are equally useful for editing masks as they are for editing image pixels. As I mentioned earlier, applying Gaussian Blur to a mask has the same effect as applying Select Feather to a selection outline. But Gaussian Blur affords more control. Where the Feather command affects all portions of a selection outline uniformly, you can apply Gaussian Blur selectively to a mask, permitting you to easily mix soft and hard edges within a single selection outline.

Another advantage to blurring a mask is that you can see the results of your adjustments on screen, instead of relying on the seldom-helpful marching ants. For example, suppose you want to create a shadow that recedes away from a subject in your composition. You’ve managed to accurately select the foreground image — but how do you feather the selection exclusively inward, so that it appears smaller than the object that casts it? Although you can pull off this feat using selection commands such as Contract and Feather, it’s much easier to apply filters such as Minimum and Gaussian Blur inside a mask. But before I go any further, I need to back up and explain how Minimum and its pal Maximum work.

Minimum and Maximum

Filter Other Minimum expands the dark portions of an image, spreading them outward into other pixels. Its opposite, Filter Other Maximum, expands the light portions of an image. In traditional stat photography, these techniques are known, respectively, as choking and spreading.

When you are working in the quick mask mode or an independent mask channel, applying the Minimum filter has the effect of incrementally contracting the selected area, subtracting pixels uniformly around the edges of the selection outline. The Minimum dialog box presents you with a single Radius value, which tells Photoshop how many edge pixels to delete. Just the opposite, the Maximum filter incrementally increases the size of white areas, which adds pixels uniformly around the edges of a selection.

Adding a cast shadow to a layer

The following steps describe how to use the Minimum and Gaussian Blur filters to contract and feather an existing selection outline to create a shadow that leans away from the foreground subject of a composition. Figures 10-37 through 10-39 illustrate the steps in the project. Figure 10-40 shows the final cast shadow.

STEPS: Filtering a Selection Outline in the Quick Mask Mode

Select the foreground image. My foreground image was the screwball character from the Corbis image library pictured in Chapter 12.) To select this scary fellow, I converted the layer’s transparency mask to a selection outline by Ctrl-clicking (z -clicking on the Mac) the layer’s name in the Layers palette.

Figure 10-37: This artificially gleeful human resides on an independent layer. To select him, I Ctrl-clicked (or z -clicked) his layer in the Layers palette.

If you’re working on a layer, switch to the background image. The quickest route is Shift+Alt+[ (that’s Shift-Option-[ on the Mac).

Press Q to enter the quick mask mode. You can create a new mask channel if you prefer, but the quick mask mode is more convenient.

Choose Filter Other Minimum. Enter a Radius value to expand the transparent area into the rubylith. In Figure 10-38, I entered a Radius value of 20 pixels. This expanded the size of the black, or masked, area and made the selection smaller.

Figure 10-38: The Minimum filter decreases the size of the transparent area in the quick mask mode, thereby choking the selection outline.

Choose Filter Blur Gaussian Blur. To create a soft shadow, I entered a Radius equal to the Radius I used in the Minimum dialog box, which was 20 pixels. Smaller values are likewise acceptable. The only potential problem with larger values is that they expand the shadow beyond the boundaries of the image, which in all probability is not the effect you want. When you click OK, Photoshop blurs the transparent area.

Press Q to exit the quick mask mode. Ah, back in the workaday world of marching ants.

Send the selection to an independent layer. The easiest way to do this is to press Ctrl+J (z -J on the Mac). You now have a shadow filled with colors from the background layer.

Choose the Multiply mode. Chapter 13, this burns the shadow into its background, so it looks darker, as a shadow should. Because your foreground image is in the way, you may not be able to see the effect of this step, but don’t worry — you will soon.

Scale and distort the shadow. Press Ctrl+T (z -T on the Mac) to invoke the Free Transform command. Then drag the top handles in the bounding box to scale the shadow; press Ctrl (z on the Mac) and drag a handle to distort the shadow, as demonstrated in Figure 10-39. For the best effect, you’ll need a big distortion. You may have to zoom out and expand the size of the image window to give yourself lots of room to work. When you get the effect you want, press Enter or Return to apply the distortion.

Figure 10-39: Press Ctrl+T (z -T on the Mac) to enter the Free Transform mode. Then Ctrl-drag (z -drag) a corner handle to distort the shadow.

Thanks to the fact that you applied the Multiply blend mode to the shadow, it appears darker than the rest of the background. You can adjust its opacity or fill it with a different color if you like. I elected to fill my background with one of Photoshop’s predefined patterns, called Molecular. As shown in Figure 10-40, this permitted me to transform the subject of my montage from an overly enthusiastic sycophant into an overly enthusiastic tour guide. As I said, you could have achieved a similar effect using Select Modify Contract and Select Feather, but unless you have a special aversion to the quick mask mode, it’s easier to be sure of your results when you can see exactly what you’re doing using filters.

Figure 10-40: Suddenly, he’s not scary anymore, he’s just passionate about his work. No doubt, we could all learn a lesson from this plainly insane man.