449 Chapter 10 ✦ Corrective Filtering Figure 10-14: The original Ike is a bit soft (left), a condition I can remedy with Unsharp Mask. Leaving the Threshold value set to 0 brings out the film grain (middle), but raising the value results in equally unattractive artifacts (right). While we wait for Photoshop to give us a better Threshold— one with a Fuzziness slider or similar control— you can create a better Threshold using a very simple masking technique. Using a few filters that I explore at greater length throughout this chapter and the next, you can devise a selection outline that traces the essen- tial edges in the image — complete with fuzzy transitions — and leaves the non- edges unmolested. So get out your favorite old vintage photograph and follow along with these steps. STEPS: Creating and Using an Edge Mask 1. Duplicate one of the color channels. Bring up the Channels palette and drag one of the color channels onto the little page icon. Ike is a grayscale image, so I duplicate the one and only channel. 2. Choose Filter ➪ Stylize ➪ Find Edges. As I explain in Chapter 11, the Find Edges filter automatically traces the edges of your image with thick, gooey outlines that are ideal for creating edge masks. 3. Press Ctrl+I. Or choose Image ➪ Adjust ➪ Invert. Find Edges produces black lines against a white background, but in order to select your edges, you need white lines against a black background. The Invert command reverses the lights and darks in the mask, as in the first example in Figure 10-15. Soft Sharpened, Threshold: 0 Sharpened, Threshold: 20 450 Part III ✦ Selections, Masks, and Filters Figure 10-15: I copy a channel, find the edges, and invert (left). I then apply a string of filters to expand and soften the edges (middle). After converting the mask to a selection outline, I reapply Unsharp Mask with winning results (right). 4. Choose Filter ➪ Noise ➪ Median. You need fat, gooey edges, and the current ones are a bit tenuous. To firm up the edges, choose the Median filter, enter a value of 2 (or thereabouts), and press Enter. 5. Choose Filter ➪ Other ➪ Maximum. The next step is to thicken up the edges. The Maximum filter expands the white areas in the image, serving much the same function in a mask as Select ➪ Modify ➪ Expand serves when editing a selection outline. Enter 4 for the Radius value and press Enter. 6. Choose Filter ➪ Blur ➪ Gaussian Blur. Unfortunately, the Maximum filter results in a bunch of little squares that don’t do much for our cause. You can merge the squares into a seamless line by choosing the Gaussian Blur command and entering 4, the same radius you entered for Maximum. Then press Enter. The completed mask is pictured in the second example of Figure 10-15. Though hardly an impressive sight to the uninitiated eye, you’re looking at the perfect edge mask — soft, natural, and extremely accurate. 7. Return to the standard composite view. Press Ctrl+tilde (~) in a color image. In a grayscale image, press Ctrl+1. 8. Convert the mask to a selection outline. Ctrl-click the mask name in the Channels palette. Photoshop selects the most essential edges in the image without selecting the grain. Find Edges, Invert Find edge mask Sharpened edges 451 Chapter 10 ✦ Corrective Filtering 9. Choose Filter ➪ Sharpen ➪ Unsharp Mask. In the last example in Figure 10-15, I applied the highest permitted Amount value, 500 percent, and a Radius of 2.0. 10. Whatever values you use, make sure the Threshold is set to 0. And always leave it at 0 from this day forward. In case Figures 10-14 and 10-15 are a little too subtle, I include enlarged views of the great general’s eyes in Figure 10-16. The top eyes show the result of using the Threshold value, the bottom eyes were created using the edge mask. Which ones appear sharper and less grainy to you? Figure 10-16: Enlarged views of the last examples from Figures 10-14 (top) and 10-15 (bottom). A good edge mask beats the Threshold value every time. Using the High Pass filter The High Pass filter falls more or less in the same camp as the sharpening filters but is not located under the Filter ➪ Sharpen submenu. This frequently overlooked gem enables you to isolate high-contrast image areas from their low-contrast counterparts. When you choose Filter ➪ Other ➪ High Pass, Photoshop offers a single option: the familiar Radius value, which can vary from 0.1 to 250.0. As demonstrated in Figure 10-17, high Radius values distinguish areas of high and low contrast only slightly. Low values change all high-contrast areas to dark gray and low-contrast areas to a slightly lighter gray. A value of 0.1 (not shown) changes all pixels in an image to a single gray value and is therefore useless. 452 Part III ✦ Selections, Masks, and Filters Figure 10-17: The results of separating high- and low-contrast areas in an image with the High Pass filter set at eight different Radius values. Applying High Pass to individual color channels In my continuing series of color plates devoted to adding a bit of digital color to the ages-old game of chess, Color Plate 10-5 shows the results of applying the High Pass filter set to a Radius value of 5.0 to the various color channels. This application is a pretty interesting use for this filter. When applied to all channels at once, High Pass 100.0 50.0 35.0 20.0 10.0 5.0 3.5 2.0 1.0 453 Chapter 10 ✦ Corrective Filtering has an irritating habit of robbing the image of color in the low-contrast areas, just where the color is needed most. But when you apply it to a single channel, there’s no color to steal. In fact, the filter adds color. For example, because there is almost no contrast in the dark shadows, High Pass elevates the black to gray in each of the affected color channels. The gray in the red channel appears red, the gray in the red channel mixed with the gray in the green channel appears yellow, and so on. As a result, the filter imbues each image with a chalky glow. I enhanced the High Pass effect slightly in Color Plate 10-5 by increasing the contrast of each affected color channel using the Levels command. Using the Input option boxes at the top of the Levels dialog box, I changed the first value to 65 and the third value to 190, thereby compressing the color space equally on both the black and white sides. Had I not done this, the images would appear a little more washed out. (Not a lot, but I figure that you deserve the best color I can deliver.) For detailed information on the Levels command, read Chapter 17. Converting an image into a line drawing The High Pass filter is especially useful as a precursor to Image➪ Adjust ➪ Threshold, which converts all pixels in an image to black and white (again, covered in Chapter 17). As illustrated in Figure 10-18, the Threshold command produces entirely different effects on images before and after you alter them with the High Pass filter. In fact, applying the High Pass filter with a low Radius value and then issuing the Threshold command converts your image into a line drawing. In the second row of examples in the figure, I followed Threshold with Filter ➪ Blur ➪ Gaussian Blur (the subject of the next section). I set the Gaussian Blur Radius value to 1.0. Like the Threshold option in the Unsharp Mask dialog box, the Threshold command results in harsh transitions; Gaussian Blur softens them to produce a more natural effect. Why change your image to a bunch of slightly different gray values and then apply a command such as Threshold? One reason is to create a mask, as discussed at length in the “Building a Mask from an Image” section of Chapter 9. (In Chapter 9, I used Levels instead of Threshold, but both are variations on the same theme.) You might also want to bolster the edges in an image. For example, to achieve the last row of examples in Figure 10-18, I layered the images prior to applying High Pass, Threshold, and Gaussian Blur. Then I monkeyed around with the Opacity setting and the blend mode to achieve an edge-tracing effect. I should mention that Photoshop provides several automated edge-tracing filters— including Find Edges, Trace Contour, and the Gallery Effects acquisition, Glowing Edges. But High Pass affords more control than any of these commands and permits you to explore a wider range of alternatives. Also worth noting, several Gallery Effects filters — most obviously Filter ➪ Sketch ➪ Photocopy — lift much of their code directly from High Pass. Although it may seem at first glance a strange effect, High Pass is one of the seminal filters in Photoshop. Note Note 454 Part III ✦ Selections, Masks, and Filters Figure 10-18: Several applications of the High Pass filter with low Radius values (top row), followed by the same images subject to Image ➪ Adjust ➪ Threshold and Filter ➪ Blur ➪ Gaussian Blur (middle). I then layered the second row onto the first and modified the Opacity and blend mode settings to create the third row. 5.0 2.5 1.0 Threshold and Gaussian Blur Opacity: 45%, Overlay mode 455 Chapter 10 ✦ Corrective Filtering 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 incre- mentally, 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. 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 discern- ing 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? Unfortunately, I don’t have any images of actresses adorned in futuristic go-go boots, so Constantine cum Rambo will have to do in a pinch. The following steps explain how to make the colossal head glow as demonstrated in Figure 10-20. STEPS: The Captain Kirk Myopia Effect 1. Press Ctrl+A to select the entire image. If you only want to apply the effect to a portion of the image, feather the selection with a radius in the neighborhood of 5 to 8 pixels. 2. Choose Filter ➪ Blur ➪ Gaussian Blur. Enter some unusually large value into the Radius option box — say, 8.0— and press Enter. 3. Press Ctrl+Shift+F to bring up the Fade dialog box. To achieve the effects shown in Figure 10-20, I reduced the Opacity value to 70 percent, making the blurred image slightly translucent. This way, you can see the hard edges of the original image through the filtered one. 456 Part III ✦ Selections, Masks, and Filters 4. You can achieve additional effects by selecting options from the Mode pop-up menu. For example, I created the upper-right example in the figure by selecting the Screen option, which uses the colors in the filtered image to lighten the original. I created the two bottom examples in the figure by applying the Darken and Lighten options. Figure 10-19: The results of blurring an image with the Gaussian Blur filter using eight different Radius values, ranging from slightly out of focus to Bad Day at the Ophthalmologist’s Office. 0.3 0.6 1.0 1.5 2.0 3.5 5.0 10.0 50.0 457 Chapter 10 ✦ Corrective Filtering Figure 10-20: After blurring the image, I chose Edit➪ Fade Gaussian Blur and changed the Opacity value to 70 percent. Then I applied the labeled blend modes to alter the image further. Color Plate 10-6 shows an image that’s more likely to interest Captain Kirk. It shows a young agrarian woman subject to most of the same settings I applied earlier to Constantine. Again, I applied the Gaussian Blur filter with a Radius of 8.0. Then I used Edit ➪ Fade Gaussian Blur to adjust the Opacity value and blend mode. The upper-left image shows the Normal mode, but the upper-right image shows the Luminosity mode. In this case, the Screen mode resulted in a washed-out effect, whereas Luminosity yielded an image with crisp color detail and fuzzy brightness values. As a result, there are some interesting places where the colors leap off her checkered dress. As in Figure 10-20, the bottom two images show the effects of the Darken and Lighten modes. 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. Normal Screen Darken Lighten 458 Part III ✦ Selections, Masks, and Filters 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 Blur Blur More 0.3 0.7 [...]... the colors of individual pixels Gaussian, 6. 25% Gaussian, 12.5% Gaussian, 18.75% Uniform, 6. 25% Uniform, 12.5% Uniform, 18.75% Figure 10-37: The Gaussian option produces more pronounced effects than the Uniform option at identical Amount values Chapter 10 ✦ Corrective Filtering Gaussian, 6. 25% Gaussian, 12.5% Gaussian, 18.75% Uniform, 6. 25% Uniform, 12.5% Uniform, 18.75% Figure 10-38: The upper-left... percentage is based on 2 56 brightness values per channel if you’re working with a 24-bit image and 32, 768 brightness values for 16- bit images So with a 24-bit image (8-bit channels), the default value of 12.5 percent is equivalent to the Photoshop 5.5 default of 32 brightness levels, which is 12.5 percent of 2 56 For example, if you enter a value of 12.5 percent for a 24-bit image, Photoshop can apply any... Noise Shown in Figure 10- 36, the Add Noise dialog box features the following options: Photoshop ✦ Amount: This value determines how far pixels in the image can stray from their current colors The value represents a color range rather than a brightness range 6 In previous versions of Photoshop, the Amount value was measured in brightness values Now, you enter a percentage value for Amount You can enter... Gaussian Blur and other Blur filters are equally as 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... adjustments on-screen, instead of relying on the seldom-helpful marching ants For example, suppose that you want to establish a buffer zone between a foreground image and its background You’ve managed to accurately select the foreground image — how do you now feather the selection exclusively outward, so that no portion of the foreground image becomes selected? Although you can pull off this feat using... Maximum and Gaussian Blur filters to feather an existing selection outline outward so that it doesn’t encroach on the foreground image 469 470 Part III ✦ Selections, Masks, and Filters STEPS: Adding a Soft Edge in the Quick Mask Mode 1 Select the foreground image As shown in Figure 10-33, my foreground image is the layered television that figured so heavily into Chapter 12 I convert the layer’s transparency... 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 465 466 Part III ✦ Selections, Masks, and Filters Select a Quality option to specify your favorite time/quality compromise The Good and Best Quality options ensure smooth results by... Threshold For example, take a look at Figure 10-31 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 actually 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 5.0, 10.0 20.0, 10.0 60 .0,... If you enter 400 percent, Photoshop theoretically can go 1024 brightness values lighter or darker But that results in colors that are out of range; therefore, they get clipped to black or white The result is higher contrast inside the noise pixels Figure 10- 36: The Add Noise dialog box asks you to specify the amount and variety of noise you want to add to the selection ✦ Uniform: Select this option... while 20.0 and 60 .0 are more 5.0, 10.0 20.0, 10.0 60 .0, 10.0 5.0, 30.0 20.0, 30.0 60 .0, 30.0 5.0, 80.0 20.0, 80.0 60 .0, 80.0 Figure 10-31: 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 467 468 Part III ✦ Selections, Masks, and Filters The Quality settings control the smoothness . outline. Enter 4 for the Radius value and press Enter. 6. Choose Filter ➪ Blur ➪ Gaussian Blur. Unfortunately, the Maximum filter results in a bunch of little squares that don’t do much for our cause is equal to about half the threshold. 5.0, 10.0 20.0, 10.0 60 .0, 10.0 5.0, 30.0 20.0, 30.0 60 .0, 30.0 5.0, 80.0 20.0, 80.0 60 .0, 80.0 468 Part III ✦ Selections, Masks, and Filters The Quality settings. Radial Blur filter, incidentally, qualifies as one of Photoshop s most time-consuming operations. Spin, Draft Spin, Best Zoom, Draft Zoom, Best 466 Part III ✦ Selections, Masks, and Filters Select