Photoshop.CS.Bible [Electronic resources] نسخه متنی

Image-Editing Theory

Like any image editor, Photoshop enables you to alter photographs and other scanned artwork. You can retouch an image, apply special effects, swap details between photos, introduce text and logos, adjust color balance, and even sharpen the focus of a photograph. Photoshop also provides everything you need to create artwork from scratch, including a suite of vector drawing tools and a highly specialized painting palette. These tools are fully compatible with pressure-sensitive tablets, so you can create naturalistic images that closely mimic watercolors and oils.

Bitmaps versus vectors

Image editors fall into the larger software category of painting programs. In a painting program, you draw a line, and the application converts it to tiny square dots called pixels. The painting itself is called a bitmapped image, but bitmap and image are equally acceptable terms.

What about other graphics applications, such as Adobe's own Illustrator? Appli-cations such as Illustrator, Macromedia FreeHand, and CorelDraw fall into a different category of software called drawing programs. Drawings comprise vector objects, which are independent, mathematically defined lines and shapes. For this reason, drawing programs are sometimes said to be vector-based or object-oriented.

As luck would have it, Photoshop spans the chasm between conventional painting and drawing programs by providing many of the best features of both. In addition to its wealth of image-editing and organic-painting capabilities, Photoshop permits you to add vector-based text and shapes to your photographic images. These features don't altogether take the place of a drawing program, but they help to make Photoshop an increasingly flexible and dynamic image-creation environment.

The ups and downs of painting

As you might expect, painting programs and drawing programs each have their strengths and weaknesses. The strength of a painting program is that it offers a straightforward approach to creating images. For example, although many of Photoshop's features are complex — exceedingly complex on occasion — its core painting tools are as easy to use as a pencil. You alternately draw and erase until you reach a desired effect, just as you've been doing since grade school.

In addition to being simple to use, each of Photoshop's core painting tools is fully customizable. It's as if you have access to an infinite variety of crayons, colored pencils, pastels, airbrushes, watercolors, and so on, all of which are erasable. Doodling on the phone book was never this much fun.

Because painting programs rely on pixels, they are ideally suited to electronic photo-graphy. Whether captured with a scanner or digital camera, an electronic photograph is composed of thousands or even tens of millions of colored pixels. A drawing program such as Illustrator may let you import such a photograph and apply very simple edits, but Photoshop gives you complete control over every pixel, entire collections of pixels, or independent elements of pixels. As witnessed by a quick examination of the pictures in this book, a photograph can become anything.

The downside of paintings and electronic photos is that they are ultimately finite in scale. Because a bitmap contains a fixed number of pixels, the resolution of an image — the number of pixels in an inch, a centimeter, or some other allotted space — changes with respect to the size at which the image is printed. Print the image small, and the pixels become tiny, which increases the resolution of the image. Like the millions of cells in your body, tiny pixels become too small to see and thus blend together to form a cohesive whole, as in the first image in Figure 1-1. Print the image large and the pixels grow, which decreases the resolution. Large pixels are like cells viewed through a microscope; once you can distinguish them independently, the image falls apart, as in the second example in the figure. The results are jagged edges and blocky transitions. The only way to remedy this problem is to increase the number of pixels in the image, which increases the size of the file on disk.

Figure 1-1: When printed small, an image appears smooth and sharp (left). But when enlarged, the image breaks down into jagged transitions and grain (right).

The downs and ups of drawing

The process of creating a vector-based drawing might more aptly be termed "constructing," because you actually build lines and shapes point by point and stack them on top of each other to create a finished image. Each object is independently editable — one of the key structural advantages of an object-oriented approach — but you're still faced with the task of building your artwork one chunk at a time.

Nevertheless, because a drawing program defines lines, shapes, and text as mathematical equations, these objects automatically conform to the full resolution of the output device, whether it's a laser printer, an imagesetter, or a film recorder. The drawing program sends the math to the printer and the printer renders the math to paper or film. In other words, the printer converts the drawing program's equations to printer pixels. Your printer offers far more pixels than your screen — a 600-dot-per-inch (dpi) laser printer, for example, offers 600 pixels per inch (dots equal pixels), whereas most screens are limited to 150 pixels per inch or fewer. So the printed drawing appears smooth and sharply focused regardless of the size at which you print it, as shown in Figure 1-2.

Figure 1-2: Small or large, a drawing prints super sharp. But it's also more work to create. Despite its simplicity, I ended up pouring several hours of labor into this piece.

Another advantage of drawings is that they take up relatively little room on disk. The file size of a drawing depends on the quantity and complexity of the objects the drawing contains. Thus, the file size has almost nothing to do with the size of the printed image, which is just the opposite of the way bitmapped images work. A thumbnail drawing of a garden that contains hundreds of leaves and petals consumes several times more disk space than a poster-sized drawing that comprises three rectangles.

When to use Photoshop

Thanks to their specialized methods, painting programs and drawing programs fulfill distinct and divergent purposes. Photoshop and other painting programs are best suited to creating and editing the following kinds of artwork:

Scanned photos, including photographic collages and embellishments that originate from scans

Images captured with any type of digital camera

Still frames captured from videotape or film

Realistic artwork that relies on the play between naturalistic highlights, midranges, and shadows

Impressionistic-type artwork and other images created for purely personal or aesthetic purposes

Logos and other display type featuring soft edges, reflections, or tapering shadows

Special effects that require the use of filters and color enhancements that you simply can't achieve in a drawing program

When to use a drawing program

You're probably better off using Illustrator or some other drawing program if you're interested in creating more stylized artwork, such as the following:

Poster art and other high-contrast graphics that heighten the appearance of reality

Architectural plans, product designs, or other precise line drawings

Business graphics, such as charts and other infographics that reflect data or show how things work

Traditional logos and text effects that require crisp, ultrasmooth edges

Brochures, flyers, and other single-page documents that mingle artwork, logos, and body-copy text (such as the text you're reading now)

If you're serious about computer graphics, you should own at least one painting program and one drawing program. If I had to rely exclusively on two graphics applications for producing still, two-dimensional images, I would choose Photoshop and Illustrator. Adobe has done a fine job of establishing symmetry between the two programs so that they share common interface elements and keyboard shortcuts. Learn one and the other makes a lot more sense.