When you get right down to it, Photoshop is really all about math. That’s right—I know some of you don’t want to hear it, but it’s true. All the actions that you can perform on an image in Photoshop rely on complex calculations of pixel color and position with respect to other variables that you specify. That’s why we let the computer do the heavy lifting, but it’s also why there are so many filters for you to play with. Each filter is a combination of changes to your image based on its underlying numbers, and since numbers are infinite, so are the possible combinations. In this hour, we look at some of the ways Photoshop can use its math prowess to sharpen, blur, and clean up your pictures.
One of the most common problems photographers face is the out-of-focus picture. A picture can turn out fuzzy for many reasons; the subject or the photographer might have moved slightly when the picture was taken, or maybe the camera focused on something other than the photo’s real subject. Regardless of how it happened, what you want to know is whether the picture can be saved.
If a photo is way out of focus, there’s not much you can do to bring it back. But if it’s only slightly soft, Photoshop can create the illusion of sharper focus. It does this with a set of filters called Sharpen, located in their own submenu on the Filter menu (see Figure 15.1).
The simplest of the Sharpen filters, Sharpen and Sharpen More, provide different levels of the same basic function. They work by finding areas in the image where there are significant color changes, such as at the edges of an object. Then Photoshop increases the contrast between adjacent pixels in those areas, making the light pixels lighter and the dark pixels darker. Figure 15.2 shows three versions of a picture of a neat bell I saw in Ohio. The top example is before sharpening. The middle example has had Sharpen applied, and the bottom example has had Sharpen More applied. If you don’t enlarge the picture too much, the Sharpen effect looks quite good. The Sharpen More effect, however, is a bit much; it exaggerates the already grainy appearance of the bell’s surface.
Be careful not to overdo the sharpening. As with the Sharpen tool, which we looked at in Hour 8, “Different Ways to Paint,” you must apply all the Sharpen filters with a light touch. Because of the way the filters enhance contrast in adjacent pixels, you might be just a click away from turning your photo to patchwork, as in Figure 15.3.
By the way, the Sharpen More filter has approximately the same effect as applying the Sharpen filter twice in a row. Most filters don’t have a “More” version, but you can always apply a filter more than once any time it has less than the desired effect. There’s even a keyboard shortcut to do just that; press Command-F (Mac) or Ctrl+F (Windows) to apply whatever filter you applied last, using the same settings (if applicable).
Try the Sharpen filter on one of your own fuzzy pictures and see what you think. Does it help? Try the Sharpen More filter as well. Both are great for quickly and painlessly adjusting slightly out-of-focus photographs or scans. They can’t really bring the picture back into focus, but they can provide the illusion of focus, and sometimes that’s good enough. Don’t forget that you can apply filters selectively, using selections to keep the filter from affecting unselected parts of the image.
Sharpen Edges doesn’t affect the whole image, so its effect isn’t as extreme as that of Sharpen More. Instead, Sharpen Edges picks out and enhances the contrast wherever it finds an edge in the image—anywhere there’s a sharp delineation between two colors. Figure 15.4 shows before and after versions of the bell, using Sharpen Edges. Sharpening the edges has a slight but noticeable effect on the quality of the photo.
Unsharp masking is a traditional technique that has been used in the printing industry for decades. Photoshop’s version of it is probably your best bet for precision sharpening. The Unsharp Mask filter locates every two adjacent pixels with a difference in brightness values greater than the Threshold value you’ve specified and increases their contrast by an amount that you also specify. Being able to control which areas are sharpened and how much sharpening is applied gives you real control over the process.
Choose Filter, Sharpen, Unsharp Mask to bring up the Unsharp Mask dialog shown in Figure 15.5. The Radius slider determines how far out from each pixel Photoshop looks for contrasting pixels to which the program can apply the sharpening effect. You’ll generally want to keep the Radius value fairly low—around 2.0 for most images, and slightly higher for high-res pictures. The Threshold setting controls how much contrast there has to be between the pixels for them to be affected. The lower the setting, the more similar the pixels can be and still be affected by the filter. The higher the setting, the fewer parts of the image will be affected. Be sure to check the Preview box so that you can see the effect of your changes in the image window as you work.
Many Photoshop experts recommend applying the Unsharp Mask filter to every image that you process, whether it will be printed or used on the Web. You should certainly try it on every image, to see whether you like the effect.
For the ultimate in sharpening power, you can turn to the Smart Sharpen filter, which Photoshop CS2 introduced. With this filter, you can choose different sharpening algorithms, or styles, for different kinds of images, and you can control the amount of sharpening in dark and light areas of your image.
Choose Filter, Sharpen, Smart Sharpen to see the Smart Sharpen options (see Figure 15.6). First, choose an option from the Remove pop-up menu. To fix a generally soft image, choose Gaussian Blur, which uses the same sharpening technique that the Unsharp Mask filter uses. If your image has a lot of detail and needs a pretty hefty amount of sharpening, choose Lens Blur to sharpen edges without adding “sharpening halos” (as shown back in Figure 15.3). And if your camera moved just as you shot the photo, choose Motion Blur and set the angle to match the angle of the blur you see in the image. Finally, unless you’re in a hurry, check the More Accurate box so that Photoshop will take a little more time on its calculations and produce the best possible result.
In Advanced mode, you’ll see two tabs in addition to the Sharpen tab, where you’ve just made your basic settings. If you’re seeing too much effect from the basic settings, but only in the shadows or only in the highlights, drag the Fade Amount slider to the left to reduce the amount of sharpening just in those areas. Drag the Tonal Width slider back and forth to determine how much of the image constitutes “shadows” or “highlights”—the higher the setting, the greater the area affected by your Shadow and Highlight tab settings. And the Radius slider controls how much of the area around each pixel Photoshop uses to decide whether that pixel falls into the category of a shadow or a highlight; unless you’re feeling adventurous, you can leave this setting alone and get perfectly fine results.
The Blur filters (Filter, Blur) are useful tools when you’re going for a soft-focus effect, whether you’re starting with a photo or working on a painting. As with the Blur tool, blurring can smooth a harshly lit portrait or, when used on a selection instead of the whole image, can throw a background out of focus so that it doesn’t distract viewers from the picture’s subject. Figure 15.7 shows the Blur filters.
As with Sharpen and Sharpen More, there are two basic Blur filters: Blur and Blur More. They do exactly what their names suggest. Blur is very subtle, and Blur More is a bit less so, about like applying the Blur filter twice in succession. Figure 15.8 shows a comparison of the two filters in use, against an unblurred 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.
You can apply the Blur filter several times to get the effect you want, or you can move right on to Gaussian Blur (Filter, Blur, Gaussian Blur), which lets you determine precisely how much the image is blurred. This filter uses a mathematical formula (the Gaussian distribution equation, which results in a bell curve) to calculate the difference in color and brightness between each pair of pixels. Most of the blurred pixels, therefore, end up in the middle of the two colors or values instead of at either end of the spectrum. This results in a generalized blur that neither darkens nor lightens the image.
The Gaussian Blur dialog (see Figure 15.9) lets you determine exactly how much blur to apply by setting a Radius value from 0.1 to 250. You can also use it to antialias the edges of an object on a layer so that the object will blend better with the background, and to blur dark shapes to create shadows. Even at fairly low settings, it has quite a dramatic effect.
Gaussian Blur is a useful retouching tool when applied to a selected area within the picture that you want to de-emphasize. In Figure 15.10, the brindle greyhound puppy is overwhelmed by the long grass in the image on the left. If I select the dog and apply a mask to hide him, I can blur the rest of the scene and call attention to the puppy (see the image on the right).
Tip: 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 you can control its effect more precisely and target just the pixels you want.
A quick application of the Blur tool, with Strength set to 75%, helps blend the blurred background into the unblurred area near the dog.
The Smart Blur filter (Filter, Blur, Smart Blur) is particularly useful for photo repair and for cosmetic retouching. It blurs everything in the image, or in the selected area of the image, except the edges. Smart Blur locates boundaries between color regions and maintains those boundaries while blurring everything within them. It’s the perfect filter when you need to take 10 years off a portrait subject’s face or get rid of the texture in a piece of cloth without losing the folds.
Figure 15.11 shows the Smart Blur filter dialog. The original photo is in the background, and you can see the change in the filter window. You can set the Radius and Threshold sliders to determine how much blur is applied and choose a Quality setting to determine how the effect is calculated.
The Smart Blur filter has three modes:
In Normal mode, the filter blurs as you would expect.
Edge Only shows you edge boundaries that Smart Blur detects, hiding the rest of the image.
Edge Overlay shows the boundaries as white lines overlaid on the image.
You can use the Edge Overlay or Edge Only mode to help you determine which Threshold value to set. Then switch the mode back to Normal and finalize your Radius setting before you click OK to apply the effect.
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 rescanned photos, although it doesn’t offer as much control as Smart Blur. The controls work just like those in the Gaussian Blur dialog.
The Radial Blur filter can produce two different kinds of circular blur effects: Spin and Zoom. The Spin option produces a blur that looks as if the image is spinning around its center point. Zoom mode is intended to look as though the camera is zooming into or away from the image.
In the Radial Blur dialog, shown in Figure 15.12, you can set both an amount for the blur effect (from 1 to 100) 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 a representation of the Amount setting in the Blur Center area as you drag the slider. You can click and drag in the Blur Center area to determine a center point for the blur effect. In Figure 15.12, I moved the center point so that it was located on the baby’s face.
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. You’re likely to notice a difference only if you’re working on a large image. But because Radial Blur doesn’t have a preview, you might find that you have to apply the filter repeatedly, undoing each time, to arrive at the right settings for your image. In that case, you’ll probably want to use Draft until you get the settings the way you want them, then switch to Best.
When we see lines drawn radiating from the back of an object or a person in a drawing, 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 moving subject. The image’s subject appears blurred against the background because it kept moving 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 cameras’ shutter speeds were slow and film was less sensitive, and therefore, required a longer exposure. Today motion blur in snapshots is unusual; you’re more likely to see it when 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. You don’t need to mess with shutter speed to achieve this effect in your pictures, however; in the Motion Blur filter, Photoshop gives you a tool that can do it.
The Motion Blur filter (choose Filter, Blur, Motion Blur) can simulate the appearance of motion by adding a directional blur to an image. In the Motion Blur dialog, shown in Figure 15.13, you can set both the Distance and the Angle of the blur according to how fast and in what direction you want the object to appear to be traveling. The Distance slider controls how far each pixel in the original image or selection is “moved” to create the blur effect; the Angle value sets the direction of the blur. The trick to getting a realistic result, however, is to select the right area to which to apply Motion Blur. To get a convincing blur, you need to blur either the subject of the photo or its background, but not both. Whatever remains unblurred in the image seems to be stationary, in contrast with the moving elements of the picture.
The Motion Blur filter doesn’t do much for most photos. After all, blurring the whole image with this filter replicates the blur caused by the camera shaking, and that’s the kind of thing we usually try to avoid, not add. But for some special effects, and for doing tricks with type, it has interesting possibilities. Figure 15.14 shows one possible use. First, I carefully selected the background of the image, around both vehicles, and then I applied Motion to the selected area.
The Lens Blur filter attempts to reproduce 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 a pentagon. Photoshop takes it a step further, letting you choose to have anywhere from three to eight sides on the highlight and specify how much of the image is involved. You can apply this filter to the entire photo, to a selection, or to a layer.
The most important thing to know about lens blur is that it can vary the amount of blur in different parts of the image based on the current selection or, if you prefer, on an alpha channel. 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.
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.
If you have some time to play around, 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 areas of the shape. This results in a very subtle effect—for 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.
I’m really not sure what Adobe intended Photoshop users to do with this 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. The esteemed technical editor of this book, Doug Nelson, likes to use Box Blur for removing dots from scanned newspaper images. If you’ve got another favorite use for this filter, drop me an email!
The Noise filters (choose Filter, Noise and pick one from the submenu) are useful for adding and removing noise from your images. What’s noise? Well, zoom way in on one of your photos. When you get to an area that should be a solid color, do you see random specks of black, white, and other colors? That’s noise; the extraneous colors are color noise, and the variance in brightness levels within a color is luminance noise. If there’s too much of it, your image looks grainy. When there’s not enough, pictures can look flat and fake. Adding noise helps blend in edits, and it can be an interesting special effect, particularly if you’re going for a vintage or distressed look. Figure 15.15 shows the Noise filters.
When you want to make your picture noisier, this is where you should head. The Add Noise filter inserts random dots throughout your image, either randomly colored or all shades of gray (if you check the Monochromatic box). The Amount slider determines just how much noise Photoshop adds, with settings ranging from 0.1% to 400%. The only other thing you have to decide is whether you want to use the Uniform or Gaussian setting for Distribution; the former creates randomly colored noise, while the latter is more likely to use colors similar to those in your picture, creating a more natural effect.
The Add Noise filter is a great starting point for experimenting with filters, most of which need to have some kind of image to work on. (Render Clouds, for example, is an exception to this rule.) If you want to create a background texture, Add Noise is usually the first filter to apply—you can get creative from there (see Figure 15.16). Add Noise also has a tremendously useful application; if your prints are showing bands of colors in areas that should be smooth, apply a tiny bit of noise before printing to tone those bands down.
Want an easy filter to apply? Here you go. Despeckle has no options and no dialog; it just does its job. And what is that? Despeckle detects the edges of objects in your picture and blurs all of the selected area or image except those edges. So if you’ve got a noisy picture that’s full of sharp color transitions, give Despeckle a try. On the other hand, if you apply Despeckle to an image that contains a lot of similarly colored objects that don’t contrast strongly with each other, the whole thing will end up blurry.
This filter is specifically designed for dealing with flaws in scanned images and vintage photos; you’ll probably never need to use it for an image shot with a digital camera. It’s like the Despeckle filter, but it offers slightly more control; you can set the blur Radius and Threshold, just as you can when using the Smart Blur filter.
Threshold controls how different pixel colors must be for the filter to affect them. Radius, on the other hand, determines how far around each pixel Photoshop looks for unusual specks or scratches. For the maximum change, you’d drag Threshold down to 0 and Radius all the way up to 16, its highest value. In the real world, however, you don’t do that, because you’ll blur the image beyond recognition. Here’s the typical procedure to follow with Dust & Scratches:
Drag the Threshold slider all the way left, to 0. This turns it off so that the filter affects the entire image.
Now drag the Radius slider left or right, or enter a value between 1 and 16. Keep adjusting it until you find the lowest value that gets rid of the objects you want to clean up.
Finally, drag the Threshold slider slowly to the right and stop at the highest value at which the image’s problems are still fixed, according to the preview (see Figure 15.17).
As you can see, using Dust & Scratches requires that you perform a balancing act, and it’s not perfect; it won’t do magic. But it’s an incredibly useful tool to anyone who’s using Photoshop to restore older photos.
If you need to smooth out a photo of a moving object, Median is the filter for you. It reduces image noise by averaging out the brightness of the pixels in the image or selection. Its only control is a Radius slider (see Figure 15.18).
If you’ve got a particularly noisy photo, or one that you want to get just right, try the Reduce Noise filter (choose Filter, Noise, Reduce Noise). It has a range of controls so you can be very precise, and you can choose to apply its changes to each color channel at a different level for the most subtle effect. Reduce Noise is the best filter for removing noise without losing image detail, and it’s the only way you can address color noise and luminance noise separately.
You’ll find four different sliders and a check box in the main section of the Reduce Noise dialog, all with interlocking effects on the noise in your image:
Strength controls how much luminance noise reduction the filter applies to the image or selection.
Preserve Details attempts to keep the filter from blurring edges and fine image details. The higher the value, the more detail you preserve, but the less noise you allow the filter to remove.
Reduce Color Noise removes color noise to a greater or lesser degree, depending on the slider setting.
Sharpen Details applies sharpening to the image after the noise-reduction process. If you prefer, you can leave this setting at 0 and sharpen the image using any of the Sharpen filters when you’re done with the Reduce Noise filter.
Remove JPEG Artifacts attempts to remove halos around objects caused by low-quality JPEG compression (see Figure 15.19).
Tip: Change the Channel
Color noise, obviously, shows up in all of a picture’s color channels. Luminance noise, on the other hand, tends to be worse in one channel, which usually turns out to be the blue channel. By using the Reduce Noise filter’s Advanced mode, you can apply noise reduction only to that channel, which helps keep image details from being blurred because they’re still completely clear in the other color channels. First, check each of the color channels in the Channels panel and decide which one you want to work on. Then choose Filter, Noise, Reduce Noise and click the Advanced radio button. Then click the Per Channel tab and choose that channel from the pop-up menu. Finally, adjust the Strength and Preserve Details sliders to produce the best results.
In this hour, you looked at some Photoshop filters that can help you rescue a bad photo or bad scan. The Sharpen filters can salvage out-of-focus photographs by increasing contrast between adjacent pixels. The most powerful of these is the Unsharp Mask filter, which lets you set the parameters for how it finds and adjusts contrasts.
Blur filters are most useful for putting unwanted parts of the picture out of focus and for softening hard edges. The Motion Blur filter enables you to create the illusion of movement in stationary objects, and the Radial Blur filter is a fun special effect.
Finally, we looked at the Noise filters, which either increase or reduce the amount of color noise and luminance noise in an image. Noise is a fact of life with today’s digital cameras, so knowing how to reduce its effect on an image is a useful skill. Adding noise to an image, on the other hand, is a great start for a variety of special effects, and the Add Noise filter can even be used on a blank canvas as a starting point for creating textures.
Find or shoot a picture of yourself or a friend, and open it in Photoshop. (If you don’t have a digital camera or scanner, download a news photo from the Web or a portrait from the book’s website—see the Introduction for the URL.) Use the Blur and Sharpen filters to improve it. Find and remove wrinkles, eye bags, uneven complexions, and any other flaws. (In Hour 21, “Repairing Black-and-White Photos,” you’ll learn more techniques for improving photos.)