SAMS Teach Yourself Adobe® Photoshop® CS2 in 24 Hours [Electronic resources] نسخه متنی

Blur Filters

The Blur filters (FilterBlur) are useful tools when you want to soften effects, either of a filter you have just applied or of brush strokes in a painting. Blurring can gently smooth a harshly lit portrait or, when used on a selection instead of the whole image, can throw an unwanted background out of focus, making it less obtrusive. The Blur filters are shown in Figure 14.7.

Figure 14.7. The Blur menu.

Blur, Blur More

There are two basic Blur filters: Blur and Blur More. They do exactly as their names suggest. Blur is very subtle. Blur More is only a little less so. Figure 14.8 shows a comparison of the two filters in use, against a nonblurred original. As you can see, the changes are minor. Blurring doesn't make much difference, but it can smooth out wrinkles in a portrait or soften a hard edge.

Figure 14.8. Blur is applied on the top right; Blur More, on the bottom right. You have to look carefully to see the effect.

Gaussian Blur

You can apply the Blur filter several times to get the effect you want, or you can move on to Gaussian Blur (FilterBlurGaussian Blur), which is a more controllable filter. It uses a mathematical formula (the Gaussian distribution equation, which results in a bell curve) to calculate the precise transition between each pair of pixels. The result of this is that most of the blurred pixels end up in the middle of the two colors or values, rather than at either end of the spectrum. This produces a generalized blur that neither darkens nor lightens the image.

The Gaussian Blur dialog box, shown in Figure 14.9, lets you determine exactly how much blur to apply by setting a Radius value from 0.1250. You can also use it to anti-alias the edges of an object, and to blur shadow areas when you want to create a drop shadow effect. Even at fairly low settings, it has quite a dramatic effect. In Figure 14.9, notice how the subject's eye and cheek wrinkles, obvious in the previous picture, are almost gone in the Blur preview area.

Figure 14.9. Smaller numbers give you less blur.

Gaussian Blur is a useful retouching tool when applied to an area within the picture that you want to de-emphasize. In Figure 14.10, there's a small lizard sunning herself on the rocks, but her protective coloration makes her kind of hard to see in the image on the left. If I select the lizard and apply a mask to hide her, I can blur the rest of the scene and call attention to the critter (see the image on the right).

Figure 14.10. Selective blurring is a helpful tool.

A quick application of the Blur tool, with Pressure set to 75%, helps to blend the blurred and unblurred areas.

Which Blur, When?

Use the Blur filters when you have a large area to blur. Use the Blur tool when you want to soften just a small area because it's more controllable in terms of the degree of focus change it applies.

Smart Blur

The Smart Blur filter (FilterBlurSmart Blur) is probably the most useful one of the bunch, especially for image editing and photo repair. It blurs everything in the image, or selection, except the edges. Smart Blur calculates the differences between color regions to determine boundaries, and it maintains these boundaries while blurring everything within them. It's the perfect filter when you need to take 10 years off a portrait subject's face, smooth out teenaged skin, or get rid of the texture in a piece of cloth without losing the folds.

Figure 14.11 shows the Smart Blur filter dialog box. The original photo is in the background, and you can see the improvements in the filter window. You can set Radius and Threshold to determine how much blur is applied and set Quality, as done earlier, to determine how the effect is calculated.

Figure 14.11. Experiment with the settings until you find the right combination of Radius and Threshold.

The Smart Blur filter has three modes:

In Normal mode, the preview area shows the effects of the blurring.
Edge Only shows you the outlines with which Smart Blur is working.
Edge Overlay shows the outlines as white lines on top of the image.

You can use the Edge Overlay or Edge Only to help you determine which Threshold value to set. Convert the mode back to Normal before you click OK to apply the effect.

Surface Blur

Even more than Smart Blur, this filter blurs an image's surfaces and background areas without obscuring edges. It's a good way to get rid of "noise" in old or re-scanned photos, although it doesn't offer as much control as Smart Blur. The controls work just like those in the Gaussian Blur dialog box.

Radial Blur

The Radial Blur filter can be interesting, if you carefully choose how to apply it. It gives you two choices: Spin and Zoom. Spin mode gives you a blur that looks as if the image is spinning around its center point. Zoom mode theoretically gives you the effect of zooming the camera into or away from the image.

In the Radial Blur dialog box, shown in Figure 14.12, you can set both an amount for the blur effect (from 1100) and a quality level (Draft, Good, or Best). Amount refers to the distance that the pixels are moved to create the blur. You can see the difference in the Blur center area as you set the blur amount. You can click and drag in the same area to determine a center point for the blur effect.

Figure 14.12. The same dialog box applies both the Zoom and Spin methods.

The Quality settings determine the manner in which the blur effect is calculated; you can choose Draft, Good, or Best. There's very little difference between Good and Best in the resulting images. The biggest difference, in fact, is not in the image quality, but in how long it takes Photoshop to compute and apply the blur in each mode. Best can take quite a long time if the image is complex and your computer is an older model.

In Figure 14.13, I've applied Spin (left) and Zoom (right) blurring to a picture of a yellow lily. After experimenting with the settings, I used 20 as the amount for Spin and 50 as the Zoom setting. You can also see these pictures in the color plate section.

Figure 14.13. Spin and Zoom obviously aren't for everyday use, but, as a special effect, they're certainly interesting.

Motion Blur

When we see lines drawn behind a car, a cat, or a comic strip character, we instinctively know that the subject is supposed to be in motion. Those lines represent

motion blur , which is actually a photographic mistake caused by using a slow shutter speed on a fast subject. The image's subject appears totally or partially blurred against the background because the subject actually traveled some distance during the fraction of a second that the camera shutter was open.

In the early days of photography, motion blur was a common occurrence, primarily because shutter speeds were slow, and film sensitivity was not very great. Today, motion blur is unusual, unless the photographer is capturing the subject this way on purpose by using the least sensitive film available or by using a small lens opening and a correspondingly slower shutter. If you want to try to approximate the effect of motion blur, Photoshop gives you a tool that can do it.

The Motion Blur (FilterBlurMotion Blur) filter can add the appearance of motion to a stationary object by placing a directional blur for a predetermined distance. In the Motion Blur dialog box, shown in Figure 14.14, you can set both the distance and direction of the blur according to how fast and in what direction you want the object to appear to be traveling. The distance sets how much of a blur is appliedor how far the original image is "moved." The angle sets the direction of the blur. To adjust, drag the Radius slider or enter precise values into the field next to it. The trick, however, is to select the right area to which to apply Motion Blur. To get a convincing blur, you need to blur the space where the object theoretically was, as well as to where it theoretically has moved.

Figure 14.14. Using the Motion Blur filter is tricky at best.

The Motion Blur filter doesn't do much for most photos. After all, the blur caused by the camera shaking is the kind of thing we usually try to avoidnot add. But, for some special effects, and for doing tricks with type, it has interesting possibilities. Figure 14.15 shows one possible use. First, I rendered the type and applied the Perspective transformation to give it some depth. Adding Motion Blur lets me run faster, but I could even take this further.

Figure 14.15. You can't run standing still.

For Figure 14.16, I set the type, placing each letter on a different layer. I then applied a different number of pixels (increasing left to right) to each Motion Blur, from 6 pixels on the

R to 30 pixels on the

N . The resulting image almost seems to be running off the screen, as shown in Figure 14.16.

Figure 14.16. Using layers lets you apply different filters or different degrees of filter to the same image.

Lens Blur

The lens blur filter attempts to simulate the "real-world" phenomenon in which lens flares and highlights take on the shape of the camera iris. Depending on the number of leaves in the camera shutter, the shape can be a hexagon or pentagon. Photoshop takes it a step further, letting you select from three to eight sides on the highlight, and how much of the image is involved. You can apply it to the entire photo, to a selection, or to a layer.

The most important thing about lens blur is that it can vary the amount of blur in different parts of the image based on the current selection. This adds depth of field to the image, so you can focus attention on the objects in the foreground and blur the objects in the background.

Average Blur

Taking blurring to the max, the Average Blur filter mixes all the colors in an image or the selected area to come up with the color that's the average of them all. Among other applications, it's a great way to choose a color that goes with everything to use for backgrounds and type.

Shape Blur

If you have some playing-around time, consider devoting some of it to this filter. Shape Blur bases its blur on an irregular shape of your choosing, repeating that shape throughout the image and applying the blurring effect more in darker areasof the shape. This results in a very subtle effectfor example, a slight starry sparkle can show up in an image blurred using a star shape. In addition to choosing a shape, you can determine how large the "kernel" image is using the Radius slider. The larger the kernel, the greater the blur effect.

Box Blur

I'm really not sure what Adobe intended Photoshop users to do with this new filter. It works like the Gaussian Blur filter, and it does pretty much the same thing, only less smoothly. An image blurred using Box Blur has more pronounced detail than the same picture blurred using a Gaussian blur with the same radius setting. Feel free to experiment, and if you figure out what Box Blur is good for, drop me an email!