Photoshop 6 for Windows Bible- P32

Chia sẻ: Cong Thanh | Ngày: | Loại File: PDF | Số trang:30

Thêm vào BST

Báo xấu

43
lượt xem 4
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Photoshop 6 for Windows Bible- P32:If you are reading this foreword, it probably means that you’ve purchased a copy of Adobe Photoshop 6.0, and for that I and the rest of the Photoshop team at Adobe thank you. If you own a previous edition of the Photoshop Bible, you probably know what to expect. If not, then get ready for an interesting trip.

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Photoshop 6 for Windows Bible- P32

Chapter A ✦ Constructing Homemade Effects 11 Figure A-13: To blur more subtly, increase the central matrix value and the Scale value by equal amounts. Edge-detection Many of you are probably beginning to get the idea by now, but just in case you’re the kind of person who believes that friends don’t let friends do math, I’ll breeze through it one more time in the venue of edge-detection. If you really want to see those edges, enter 1s and 2s into the neighboring options in the matrix and then enter a CMV just small enough — it’s a negative value, after all — to make the sum 1. Examples appear in Figure A-14 for your viewing pleasure. Figure A-14: To create severe edge-detection effects, enter a negative CMV just small enough to compensate for the positive values in the matrix.
12 Extra Reading ✦ Photoshop 6 for Windows Bible To lighten the edges and bring out the blur, raise the CMV and enter the resulting sum into the Scale option box. The first example in Figure A-15 pushes the bound- aries between edge-detection and a straight blur. Figure A-15: To blur the edges, increase the central matrix value and then enter the sum into the Scale value. Non-1 variations Every image shown in Figures A-7 through A-15 is the result of manipulating matrix values and using the Scale option to produce a sum total of 1. Earlier in this chap- ter, I showed you what can happen if you go below 1 (black images) or above 1 (white images). But I haven’t shown you how you can use non-1 totals to produce interesting, if somewhat washed-out, effects. The key is to raise the Offset value, thereby adding a specified brightness value to each pixel in the image. By doing this, you can offset the lightening or darkening caused by the matrix values to create an image that has half a chance of printing. Lightening overly dark effects The first image in Figure A-16 uses nearly the exact same values used to create the extreme sharpening effect in the last image of Figure A-8. The only difference is that the CMV is 1 lower (8, down from 9), which in turn lowers the sum total from 1 to 0. The result is an extremely dark image with hints of brightness at points of high con- trast. The image looks okay on screen — actually, it looks pretty cool because of all those little star-like sprinkles in it — but it’s likely to fill in during the printing pro- cess. If the first image in Figure A-16 looks like anything but a vague blob of black- ness, it’s a miracle. Most people would kiss this image good-bye, and rightly so. It’s too darn dark.
Chapter A ✦ Constructing Homemade Effects 13 Figure A-16: Three examples of sharpening effects with sum totals of 0. I lightened the images incrementally by entering positive values into the Offset option box. To prevent the image from filling in, lighten the image using the Offset value. Photo- shop adds the value to the brightness level of each selected pixel. A brightness value of 255 equals solid white, so you don’t need to go too high. As illustrated by the last example in Figure A-16, an Offset value of 100 is enough to raise most pixels in the image to a medium gray. Figure A-17 shows the results of lightening an overly dark edge-detection effect using the Offset value. Figure A-17: Three examples of edge-detection effects with sum totals of 0, lightened incrementally by using progressively higher Offset values.
14 Extra Reading ✦ Photoshop 6 for Windows Bible Darkening overly light effects You also can use the Offset value to darken filtering effects with sum totals greater than 1. The images in Figures A-18 and A-19 show sharpening and edge-detection effects whose matrix totals amount to 2. On their own, these filters produce effects that are too light. However, as demonstrated in the middle and right examples in the figures, you can darken the effects of the Custom filter to create high-contrast images by entering a negative value into the Offset option box. Figure A-18: Three examples of sharpening effects with sum totals of 2. I darkened the images incrementally by entering negative values into the Offset option box. Figure A-19: Three examples of edge-detection effects with sum totals of 2, darkened incrementally with progressively lower Offset values.
Chapter A ✦ Constructing Homemade Effects 15 Using extreme offsets If a brightness value of 255 produces solid white and a brightness value of 0 is solid black, why in blue blazes does the Offset value permit any number between negative and positive 9,999, a number 40 times greater than solid white? The answer lies in the fact that the matrix options can force the Custom filter to calculate brightness values much darker than black and much lighter than white. Therefore, you can use a very high or very low Offset value to boost the brightness of an image in which all pixels are well below black or diminish the brightness when all pixels are way beyond white. Figure A-20 shows exaggerated versions of the sharpening, blurring, and edge- detection effects. The sum totals of the matrixes are –42, 54, and 42, respectively. Without some help from the Offset value, each of these filters would turn every pixel in the image black (in the case of the sharpening effect) or white (blurring and edge-detection). But as demonstrated in the figure, using enormous Offset numbers brings out those few brightness values that remain. The images are so polarized that there’s hardly any difference between the three effects, except that the first image is an inverted version of the other two. The difference is even less noticeable if you lower the opacity of the effect using Filter ➪ Fade, as demonstrated in the sec- ond row of examples in Figure A-20. Figure A-20: You can create high-contrast effects by exaggerating all values in the matrix and then compensating by entering a very high or very low Offset value (top row). When you back off the effect using Filter ➪ Fade (bottom row), these dramatic effects are barely discernible.
16 Extra Reading ✦ Photoshop 6 for Windows Bible Figure A-21: Enter positive matrix values in a horizontal formation (left) or vertical formation (middle) to create slight motion blurs. By positioning positive values in opposite corners of the matrix, you create a vibrating effect (right). Directional sharpening To selectively sharpen edges in an image based on the angles of the edges, you can organize negative and positive matrix values into rows or columns. For example, to sharpen only the horizontal edges in an image, fill the middle row of matrix options with positive values and the rows immediately above and below with negative val- ues, as demonstrated in the left example in Figure A-22. Similarly, you can sharpen only the vertical edges by entering positive values in the middle column and flank- ing the column on left and right with negative values, as shown in the middle exam- ple in the figure. In the last example, I arranged the positive values along a diagonal axis to sharpen only the diagonal edges. You even can combine directional sharpening with directional blurring. Figure A-23 shows the first example from Figure A-22 blurred both horizontally and vertically. To blur the image horizontally, as in the middle example of Figure A-23, I added pos- itive values to the extreme ends of the middle row, thereby extending the range of the filter and creating a sort of horizontal jumbling effect. To blur the image verti- cally, as in the final example of the figure, I added positive values to the ends of the middle column.
Chapter A ✦ Constructing Homemade Effects 17 Figure A-22: Arrange positive values in a row (left), column (middle), or along a diagonal axis (right) to sharpen horizontal, vertical, and diagonal edges exclusively. Figure A-23: The image from Figure A-22 (left) blurred horizontally (middle) and vertically (right).
18 Extra Reading ✦ Photoshop 6 for Windows Bible Embossing So far, we aren’t going very nuts, are we? Despite their unusual formations, the matrix values in Figures A-21 through A-23 still manage to maintain symmetry. Well, now it’s time to lose the symmetry, which typically results in an embossing effect. Figure A-24 shows three variations on embossing, all of which involve positive and negative matrix values positioned on opposite sides of the CMV. (The CMV happens to be positive merely to maintain a sum total of 1.) Figure A-24: You can create embossing effects by distributing positive and negative values on opposite sides of the central matrix value. This type of embossing has no hard and fast light source, but you might imagine that the light comes from the general direction of the positive values. Therefore, when I swapped the positive and negative values throughout the matrix (all except the CMV), I approximated an underlighting effect, as demonstrated by the images in Figure A-25. In truth, it’s not so much a lighting difference as a difference in edge enhancement. White pixels collect on the side of an edge represented by positive values in the matrix; black pixels collect on the negative-value side. So when I swapped the loca- tions of positive and negative values between Figures A-24 and A-25, I changed the distribution of white and black pixels in the filtered images.
Chapter A ✦ Constructing Homemade Effects 19 Figure A-25: Change the location of positive and negative matrix values to change the general direction of the light source. Embossing is the loosest of the Custom filter effects. As long as you position posi- tive and negative values on opposite sides of the CMV, you can distribute the values in almost any way you see fit. Figure A-26 demonstrates three entirely arbitrary arrangements of values in the Custom matrix. Figure A-27 shows those same effects downplayed by raising the CMV and entering the sum of the matrix values into the Scale option box. Figure A-26: You can create whole libraries of embossing effects by experimenting with different combinations of positive and negative values.
20 Extra Reading ✦ Photoshop 6 for Windows Bible Figure A-27: To emboss more subtly, increase the central matrix value and the Scale values by equal amounts. Incidentally, the main advantage of using the Custom filter rather than using Filter ➪ Stylize ➪ Emboss to produce embossing effects is that Custom preserves the colors in an image while Emboss sacrifices color and changes low-contrast portions of an image to gray. Figure A-28 shows the matrix values from the first example of Figure A-26 applied to a color image. It also shows examples of other Custom effects, including variations on sharpening and edge-detection. If you become enthralled with convolution kernels and you feel compelled to explore them in more detail, you may want to check out a $200 plug-in called KPT Convolver from MetaCreations. Although steeply priced, it permits you to explore convolutions using a more intuitive interface and without using any math. Convolver doesn’t do anything that you can’t already do with the Custom filter, but it can simultaneously apply different convolutions to separate color channels, and it permits you to investigate filtering possibilities that you aren’t likely to discover on your own.
Chapter A ✦ Constructing Homemade Effects 21 Figure A-28: Color versions of four Custom filter effects, including (clockwise from upper left) mild sharpening, offset sharpening, edge-detection, and full-color embossing. Displacing Pixels in an Image Photoshop’s second custom effects filter is Filter ➪ Distort ➪ Displace, which enables you to distort and add texture to an image by moving the colors of certain pixels in a selection. You specify the direction and distance that the Displace filter moves colors by creating a second image called a displacement map, or dmap (pro- nounced dee-map) for short. The brightness values in the displacement map tell Photoshop which pixels to affect and how far to move the colors of those pixels: ✦ Black: The black areas of the displacement map move the colors of corre- sponding pixels in the selection a maximum prescribed distance to the right and/or down. Lighter values between black and medium gray move colors a shorter distance in the same direction.
22 Extra Reading ✦ Photoshop 6 for Windows Bible ✦ White: The white areas move the colors of corresponding pixels a maximum distance to the left and/or up. Darker values between white and medium gray move colors a shorter distance in the same direction. ✦ Medium gray: A 50 percent brightness value, such as medium gray, ensures that the colors of corresponding pixels remain unmoved. Suppose that I create a new image window the same size as the scan of the Egyptian temple carving that I’ve used about sixty times now in this chapter. This new image will serve as the displacement map. I divide the image into four quadrants. As shown in the middle example of Figure A-29, I fill the upper left quadrant with black, the lower right quadrant with white, and the other two quadrants with medium gray. (The arrows indicate the direction in which the quadrants will move colors in the affected image. They do not actually appear in the dmap.) When finished, I save the dmap to disk in the native Photoshop format so that the Displace filter can access it. I then return to the Egyptian carving image, choose Filter ➪ Distort ➪ Displace, edit the settings as desired, and open the dmap from disk. The result is the image shown in the last example of Figure A-29. In keeping with the distribution of brightness values in the dmap, the colors of the pixels in the upper left quadrant of the carving image move rightward, the colors of the pix- els in the lower right quadrant move to the left, and the colors in the upper right and lower left quadrant remain intact. Figure A-29: The Displace filter moves colors in an image (left) according to the brightness values in a separate image, called the displacement map (middle). The arrows indicate the direction that the map moves colors in the image (right). Note A dmap must be a color or grayscale image, and you must save the dmap as a flat- tened image in the native Photoshop file format. (If you want to be absolutely sure there are no layers, use the Photoshop 2.0 format.) The Displace command does not recognize PICT, TIFF, or any of the other nonnative file formats. Who knows why? Those programmers move in mysterious ways.
Chapter A ✦ Constructing Homemade Effects 23 At this point, you likely have two questions: How do you use the Displace filter, and why in the name of all that is good would you possibly want to? The hows of the Displace filter are covered in the following section. To discover some whys — which should in turn help you dream up some whys of your own — read the “Using Displacement Maps” section later in this chapter. Displacement theory Like any custom filtering effect worth its weight in table salt — an asset that has taken something of a nose dive in the recent millennium — you need a certain degree of mathematical reasoning skills to predict the outcome of the Displace fil- ter. Though I was a math major in college (well, actually, I double-majored in math and fine arts, and I must admit to paying the lion’s share of attention to the latter), I frankly was befuddled by the results of my first few experiments with the Displace command. Don’t be surprised if you are as well. With some time and a modicum of effort, however, you can learn to anticipate the approximate effects of this filter. Direction of displacement Earlier, I mentioned — and I quote — “The black areas of the displacement map move . . . colors . . . to the right and/or down . . . the white areas move . . . colors . . . to the left and/or up.” Yikes, talk about your fragmented quotations. I think I’ll sue! Anyway, the point is, you may have wondered to yourself what all this “and/or” guff was all about. “Is it right or is it down?” you may have puzzled, and rightly so. The truth is that the direction of a displacement can go either way. It’s up to you. If you like right, go with it. If you like down, don’t let me stop you. If you like both together, by all means, have at it. Beginning to understand? No? Well, it works like this: A dmap can contain one or more color channels. If the dmap is a grayscale image with one color channel only, the Displace filter moves colors that correspond to black areas in the dmap both to the right and down, depending on your specifications in the Displace dialog box. The filter moves colors that correspond to white areas in the dmap both to the left and up. Figure A-30 shows two examples of an image displaced using a single-channel dmap, which appears on the left side of the figure. (Again, the arrows illustrate the direc- tions in which different brightness values move colors in the affected image. They are not part of the dmap file.) I displaced the middle image at 10 percent and the right image at 20 percent. Therefore, the colors in the right image travel twice the distance as those in the middle image, but all colors travel the same direction. (The upcoming section “The Displace dialog box” explains exactly how the percentage values work.)
24 Extra Reading ✦ Photoshop 6 for Windows Bible Figure A-30: The results of applying a single-channel displacement map (left) to an image at 10 percent (middle) and 20 percent (right). However, if the dmap contains more than one channel — whether it’s a color image or a grayscale image with an independent mask channel — the first channel indi- cates horizontal displacement, and the second channel indicates vertical displace- ment. All other channels are ignored. Therefore, the Displace filter moves colors that correspond to black areas in the first channel of the dmap to the right and col- ors that correspond to white areas to the left. (Again, this depends on your specifi- cations in the Displace dialog box.) The filter then moves colors that correspond to the black areas in the second channel downward and colors that correspond to white areas upward. Figure A-31 shows the effect of a two-channel dmap on our friend the pharaoh. The top row shows the appearance and effect of the first channel on the image at 10 per- cent and 20 percent. The bottom row shows the appearance and effect of the sec- ond channel. Brightness value transitions If you study Figure A-31 for any length of time, you’ll notice a marked stretching effect around the edges of the image, particularly around the two right images. This is an effect you want to avoid. The cause of the effect is twofold: First, the transition from gray to black and gray to white pixels around the perimeter of the dmap is relatively quick, especially com- pared with the gradual transitions in the central portion of the image. Second, tran- sitions — reading from left to right, or top to bottom — produce a more noticeable effect when they progress from light to dark than when they progress from dark to light. The reason for this is that these transitions follow the direction of Photo- shop’s displacement algorithm. (I know, when I throw in a word like algorithm, everybody’s eyes glaze over, but try to stick with me.)
Chapter A ✦ Constructing Homemade Effects 25 Figure A-31: The horizontal (top row) and vertical (bottom row) results of applying a two-channel displacement map (left column) to an image at 10 percent (middle) and 20 percent (right). For example, in the light-to-dark transition on the left side of the first-channel dmap in Figure A-31, one gray value nudges selected colors slightly to the right, the next darker value nudges them an extra pixel, the next darker value another pixel, and so on, resulting in a machine-gun displacement effect that creates a continuous stream of the same colors over and over again. Hence, the big stretch. Get it? Well, if not, the important part is this: To avoid stretching an image, make your dmap transitions slow when progressing from light to dark and quick when progressing from dark to light. For example, in the revised dmap channels shown in the left column of Figure A-32, the gray values progress slowly from gray to black, abruptly from black to gray to white, and then slowly again from white to gray. Slow light to dark, fast dark to light. The results are smoother image distortions, as demonstrated in the middle and right columns of the figure.
26 Extra Reading ✦ Photoshop 6 for Windows Bible Figure A-32: Changing the speeds of color transitions in the two-channel displacement map (left column) created smoother image distortions at both the 10 percent (middle) and 20 percent (right) settings. The Displace dialog box When you choose Filter ➪ Distort ➪ Displace, Photoshop displays the Displace dia- log box. (“Displays the Displace” is the modern equivalent of “Begin the Beguine,” don’t you know.) As shown in Figure A-33, the Displace dialog box provides the fol- lowing options: ✦ Scale: You can specify the degree to which the Displace filter moves colors in an image by entering percentage values into the Horizontal Scale and Vertical Scale option boxes. At 100 percent, black and white areas in the dmap each have the effect of moving colors 128 pixels. That’s 1 pixel per each brightness value over or under medium gray. You can isolate the effect of a single-channel dmap vertically or horizontally — or ignore the first or second channel of a two-channel dmap — by entering 0 percent into the Horizontal or Vertical option box, respectively.
Chapter A ✦ Constructing Homemade Effects 27 Figure A-33: Use these options to specify the degree of distortion, how the filter matches the displacement map to the image, and how it colors the pixels around the perimeter of the selection. Figure A-34 shows the effect of distorting an image exclusively horizontally (top row) and vertically (bottom row) at each of three percentage values: 5 percent, 15 percent, and 30 percent. In each case, I used the two-channel dmap from Figure A-32. Figure A-34: The results of applying the Distort filter exclusively horizontally (top row) and exclusively vertically (bottom row) at 5 percent (left column), 15 percent (middle), and 30 percent (right).
28 Extra Reading ✦ Photoshop 6 for Windows Bible ✦ Displacement Map: If the dmap contains fewer pixels than the image, you can either scale it to match the size of the selected image by selecting the Stretch to Fit radio button or repeat the dmap over and over within the image by selecting Tile. Figure A-35 shows a small two-channel dmap that contains radial gradations. In the first column, I stretched the dmap to fit the image. In the second column, I tiled the dmap. To create both examples in the top row, I set the Horizontal Scale and Vertical Scale values to 10 percent. To create the bottom-row examples, I raised the values to 50 percent. Figure A-35: Using a small, two-channel dmap (offset top left), I stretched the dmap to fit (left column) and tiled it (right column) at 10 percent (top row) and 50 percent (bottom row). ✦ Undefined Areas: These radio buttons let you tell Photoshop how to color pixels around the outskirts of the selection that are otherwise undefined. By default, the Repeat Edge Pixels radio button is selected, which repeats the col- ors of pixels around the perimeter of the selection. This can result in extreme stretching effects, as shown in the middle example of Figure A-36. To repeat the image inside the undefined areas instead, as demonstrated in the final example of the figure, select the Wrap Around option.
Chapter A ✦ Constructing Homemade Effects 29 Tip The Repeat Edge Pixels setting was active in all displacement map figures prior to Figure A-36. In these cases, I frequently avoided stretching effects by coloring the edges of the dmap with medium gray and gradually lightening or darkening the brightness values toward the center. Figure A-36: After creating a straightforward, single-channel displacement map (left), I applied the filter subject to two different Undefined Areas settings, Repeat Edge Pixels (middle) and Wrap Around (right). After you finish specifying options in the Displace dialog box, press Enter to display the Open dialog box, which enables you to select the displacement map saved to disk. Only native Photoshop documents show up in the scrolling list. Using Displacement Maps So far, all the displacement maps demonstrated involve gradations of one form or another. Gradient dmaps distort the image over the contours of a fluid surface, like a reflection in a fun-house mirror. In this respect, the effects of the Displace filter closely resemble those of the Pinch and Spherize filters described in the last chap- ter. But the more functional and straightforward application of the Displace filter is to add texture to an image. Creating texture effects Figure A-37 shows the results of using the Displace filter to apply nine of the pat- terns from the DispMaps folder inside the Filters\Plug-Ins folder. Figure A-38 shows the effects of applying four of the patterns to color images. Introduced in Chapter 10, this folder contains repeating patterns that Adobe designed especially with the Displace filter in mind.
30 Extra Reading ✦ Photoshop 6 for Windows Bible 12-sided Crumbles Fragment layers Mezzo effect Random strokes Rectangular tiles Schnable effect Streaks pattern Twirl pattern Figure A-37: These are examples of applying nine patterns from the Displacement Maps folder with the Displace filter at 10 percent horizontally and vertically.