Chapter 10: Corrective Filtering - Photoshop.CS.Bible [Electronic resources] نسخه متنی

Chapter 10: Corrective Filtering

Filter Basics

In Photoshop, filters enable you to apply automated effects to an image. Although named after photographers’ filters, which typically correct lighting fluctuations and perspective, Photoshop’s filters can accomplish a great deal more. You can slightly increase the focus of an image, introduce random pixels, add depth to an image, or completely rip it apart and reassemble it into a murky pile of goo. Any number of special effects are made available via filters.

At this point, a little bell should be ringing in your head, telling you to beware of standardized special effects. Why? Because everyone who has Photoshop — or its cocky young offspring, Photoshop Elements — has access to the same filters that you do. If you rely on filters to edit your images for you, your audience will quickly recognize your work as poor or at least unremarkable art.

Imagine this scenario: You’re wasting away in front of your TV, flipping aimlessly through the channels. Just as your brain is about to shrivel and implode, you stumble across that really cool commercial for an SUV where it keeps rolling along implacably as the background behind it changes something like 17 times. Really eye-catching, unusual stuff, and I would say it was a terrific commercial if only I could remember precisely which SUV it was selling. Ah, well.

The commercial ends, and you’re so busy basking in the glow that you neglect for a split second to whack the channel- changer. Before you know it, you’re midway through an advertisement for a monster truck rally. Like the SUV commercial, this ad is riddled with special effects — spinning letters, a reverberating voice-over slowed down to an octave below the narrator’s normal pitch, and lots of big machines filled with little men filled with single brain cells working overtime. Watching this obnoxious commercial is like being beaten over the head with a sledgehammer and then run over several times by a steamroller for good measure.

You see, in and of themselves, special effects aren’t bad. It’s all in how you use them. The SUV commercial manages to entice your eye and draw you into its constantly morphing world, making the vehicle look very hip and cool. The monster truck rally’s effects are more of the hard-sell, hit-you-over-the-head variety. Not only are these effects devoid of substance, but also, more importantly, they’re devoid of creativity.

This chapter and the next are about the creative application of special effects. Rather than trying to show an image subject to every single filter — a service already performed quite adequately by the manual included with your software — these chapters explain exactly how the most important filters work and offer some concrete ways to use them.

You also learn how to apply several filters in tandem and how to use filters to edit images and selection outlines. My goal is to teach you not so much which filters are available — you can find that out by tugging on the Filter menu — but how and when to use filters.

A first look at filters

You access Photoshop’s special-effects filters by choosing commands from the Filter menu. These commands fall into two general camps: corrective and destructive.

Corrective filters

Corrective filters are workaday tools that you use to modify scanned or otherwise captured images and to prepare an image for printing or screen display. In many cases, the effects are subtle enough that the viewer won’t even notice that you applied a corrective filter. As demonstrated in Figure 10-1, these filters include those that change the focus of an image, enhance color transitions, and average the colors of neighboring pixels. You can find these filters in the Filter Blur, Noise, Sharpen, and Other submenus.

Figure 10-1: A woman getting a facial subject to four corrective filters, including one each from the Sharpen, Blur, Other, and Noise submenus (reading clockwise from upper left).

Many corrective filters have direct opposites. Blur is the opposite of Sharpen, Add Noise is the opposite of Median, and so on. This is not to say that one filter entirely removes the effect of the other; only reversion functions such as the History palette provide that capability. Instead, two opposite filters produce contrasting effects.

Corrective filters are the subject of this chapter. Although they number fewer than their destructive counterparts, I spend more time on them because they represent the functions you’re most likely to use on a day-to-day basis.

Destructive filters

The destructive filters produce effects so dramatic that they can, if used improperly, completely overwhelm your artwork, making the filter more important than the image itself. For the most part, destructive filters reside in the Filter Distort, Pixelate, Render, and Stylize submenus. A few examples of overwhelmed images appear in Figure 10-2.

Figure 10-2: The effects of applying four destructive filters, one each from the Distort, Pixelate, Stylize, and Render submenus (clockwise from upper left). Note that Lighting Effects is applicable to only color images, so I had to convert the image to the RGB mode before applying the filter.

Destructive filters produce way-cool effects, and many people gravitate toward them when first experimenting with Photoshop. But the filters invariably destroy the original clarity and composition of the image. Granted, every Photoshop function is destructive to a certain extent, but destructive filters change your image so extensively that you can’t easily disguise the changes later by applying other filters or editing techniques.

Destructive filters are the subject of Chapter 11. Rather than explaining every one of these filters in detail, I try to provide a general overview.

Effects filters

Photoshop also provides a subset of 47 destructive filters called the effects filters. These filters originally sire from the Gallery Effects collection, developed by Silicon Beach, which was gobbled up by Aldus (of PageMaker fame) and finally acquired by Adobe Systems. Not knowing what exactly to do with this grab bag of plug-ins, Adobe integrated them into Photoshop.

In addition to the Filter Gallery dialog box, most of the effects filters also reside in the Filter Artistic, Brush Strokes, Sketch, and Texture submenus (see Figure 10-3 for some examples). A few have trickled out into other submenus, including FilterDistort Diffuse Glow, Glass, and Ocean Ripple; and Filter Stylize Glowing Edges.

Figure 10-3: The effects filters come from Gallery Effects, a little toy surprise that Adobe accidentally acquired when it purchased Aldus Corporation. Here we see the impact of one filter each from the Filter Artistic, Brush Strokes, Texture, and Sketch submenus (clockwise from upper left).

How filters work

When you choose a command from the Filter menu, Photoshop applies the filter to the selected portion of the image on the current layer. If no portion of the image is selected, Photoshop applies the filter to the entire layer. Therefore, if you want to filter every nook and cranny of the current layer, press Ctrl+D (z -D on the Mac) to cancel any existing selection outline and then choose the desired command.

External plug-ins

Some filters are built into the Photoshop application. Others are external modules that reside in the Plug-Ins folder. This enables you to add functionality to Photoshop by purchasing additional filters from third-party collections. Gallery Effects used to be such a collection. Eye Candy, from Alien Skin, is another popular collection.

If you open the Plug-Ins folder inside the Photoshop folder, you see that it contains several subfolders. By default, Photoshop places the filters in the Filters and Effects subfolders, but you can place additional filters anywhere inside the Plug-Ins folder. Even if you create a new folder inside the Plug-Ins folder and call it No Filters Here, create another folder inside that called Honest, Fresh Out of Filters, toss in one more folder called Carpet Beetles Only, and put every plug-in you own inside this latest folder, Photoshop sees through your clever ruse and displays the exact same filters you always see under their same submenus in the Filter menu. The only purpose of the subfolders is to keep things tidy, so that you don’t have to look through a list of 6,000 files.

Previewing filters

For years, the biggest problem with Photoshop’s filters was that none offered previews to help you predict the outcome of an effect. You just had to tweak your 15,000 meaningless settings and hope for the best. But today, life is much better. Photoshop 3 introduced previews, Version 4 made them commonly available to all but the most gnarly filters, and subsequent versions have had the good sense to leave well enough alone.

Photoshop offers two previewing capabilities:

Dialog box previews: Labeled in Figure 10-4, the 100100-pixel preview box is now a common feature of all filter dialog boxes. Drag inside the preview box to scroll the portion of the image you want to preview. Move the cursor outside the dialog box to get the square preview cursor (labeled in the figure). Click with the cursor to center the contents of the preview box at the clicked position in the image.

Figure 10-4: Most filter dialog boxes let you preview the effects of the filter in both the dialog box and the image window.

Click the zoom buttons (+ and –) to change the view of the image in the preview box. You can even take advantage of the standard zoom tool by pressing Ctrl+spacebar or Alt+spacebar (z -spacebar or Option-spacebar on the Mac), depending on whether you want to zoom in or out.

TipImage window previews: Most corrective filters — as well as a few destructives such as Mosaic and Emboss — also preview effects in the full image window. Just select the Preview check box to activate this function. While the effect is previewing, a blinking progress line appears under the zoom value in the dialog box. In Figure 10-4, for example, you can see that the bottom of the image still hasn’t finished previewing, so the progress line strobes away. If you’re working on a relatively poky computer, you’ll probably want to turn the Preview check box off to speed up the pace at which the filter functions.

Even though a dialog box is on screen and active, you can zoom and scroll the contents of the image window. Ctrl+spacebar-click (z -spacebar-click on the Mac) to zoom in; Alt+spacebar-click (Option-spacebar-click on the Mac) to zoom out. Or you can zoom in and out by pressing Ctrl+plus and Ctrl+minus (z -plus and z -minus on the Mac), respectively. Spacebar-drag to scroll. You can also choose commands from the View and Window menus.

Most destructive filters make no attempt to preview effects in the image window. And six filters continue to offer no previews whatsoever: Radial Blur, Displace, Color Halftone, Extrude, Tiles, and De-Interlace. Of course, single-shot filters — the ones that don’t bring up dialog boxes — don’t need previews because there aren’t any settings to adjust.

Reapplying the last filter

Both techniques work even if you undo the last application of a filter. However, if you cancel a filter in progress, pressing Ctrl+F or Ctrl+Alt+F (z -F or z -Option-F on the Mac) applies the last uncanceled filter.

Nudging numerical values

If the value accommodates decimal values, it’s probably more sensitive to the arrow key. Press an arrow for a 0.1 change; press Shift+arrow for 1.0.

Fading a filter

In many cases, you apply filters to a selection or an image at full intensity — meaning that you marquee an area using a selection tool, choose a filter command, enter whatever settings you deem appropriate if a dialog box appears, and sit back and watch the fireworks.

What’s so full intensity about that? Sounds normal, right? Well, the fact is, you can reduce the intensity of the last filter applied by choosing Edit Fade or by pressing Ctrl+Shift+F (z -Shift-F on the Mac). This command permits you to mix the filtered image with the original, unfiltered one.

As shown in Figure 10-5, the Fade dialog box provides you with the basic tools of image mixing — an Opacity value and a blend mode pop-up menu. To demonstrate the wonders of Edit Fade, I’ve applied two particularly destructive Gallery Effects filters to the woman getting a facial — Filter Stylize Glowing Edges and FilterSketch Bas Relief. The right-hand images show the effects of pressing Ctrl+Shift+F and applying two blend modes, Screen and Vivid Light, with the Opacity value set to 100 and 65 percent, respectively.

Figure 10-5: Press Ctrl+Shift+F (z -Shift-F on the Mac) to mix the filtered image with the unfiltered original. I don’t know about you, but I’d take a Glowing Edges facial over a Bas Relief one any day.

Creating layered effects

Therefore, you may find it more helpful to copy a selection to a separate layer (by pressing Ctrl+J on the PC or z -J on the Mac) before applying a filter. This way, you can perform other operations, and even apply many filters in a row, before mixing the filtered image with the underlying original.

Filtering inside a border

And here’s another reason to layer before you filter: If your image has a border around it — like the ones shown in Figure 10-6 — you don’t want Photoshop to factor the border into the filtering operation. To avoid this, select the image inside the border and press Ctrl+J (Win) or z -J (Mac) to layer it before applying the filter. The reason this works is that most filters take neighboring pixels into consideration even if they are not selected. By contrast, when a selection floats, it has no neighboring pixels, and therefore the filter affects the selected pixels only.

Figure 10-6: The results of applying two sample filters to images surrounded by borders. In each case, only the image was selected; the border was not. Layering the right examples prevented the borders from affecting the performance of the filters.

Figure 10-6 shows the results of applying two filters discussed in this chapter — Unsharp Mask and Motion Blur — when the image is anchored in place and when it’s layered. In all cases, the 2-pixel border was not selected. In the left examples, the Unsharp Mask filter leaves a high-contrast residue around the edge of the image, and Motion Blur duplicates the left and right edges of the border. Both problems vanish when the filters are applied to layered images, as seen on the right.

Even if the area outside the selection is not a border per se — perhaps it’s just a comparatively dark or light area that serves as a visual frame — layering comes in handy. You should always layer the selection unless you specifically want edge pixels to be calculated by the filter.

Undoing a sequence of filters

Okay, here’s one last reason to layer before you filter. Copying an image to a layer protects the underlying image. If you just want to experiment a little, pressing Ctrl+J (z -J on the Mac) is often more convenient than restoring a state in the History palette. After applying four or five effects to a layer, you can undo all that automated abuse by Alt-clicking (Win) or Option-clicking (Mac) the trash icon at the bottom of the Layers palette, which deletes the layer. The underlying original remains unharmed.