TE RI AL Working with Digital Images C TE D MA amera film and photographic prints are not yet things of the past, and hopefully, there will always be a place for these beloved mediums. But humans continue to be endowed with certain irresistible compulsions, not the least of which is the pursuit of convenience. The instant gratification of digital imaging, along with the improvement of its quality, has contributed to making it the standard of today.
Part I Welcome to Adobe Photoshop CS4 FIGURE 1.1 Some of the individual pixels in an image are magnified and shown here. Color and lightness qualities of digital images The following terminology is helpful to know when learning about the types of digital images: n Tonal range (or dynamic range). This term refers to the range of dark to light values in an image, usually referred to as shadows, midtones, and highlights.
Working with Digital Images Hue, Saturation, and Brightness The Hue, Saturation, and Brightness (HSB) color model is not a color mode that can be assigned to an image in Photoshop, but it is a useful way of organizing color components. The HSB model is helpful in understanding the meaning of the terms Hue, Saturation, and Brightness. In the HSB model, the hue is specified as an angle from 0° to 360° that corresponds to a location on the color wheel.
Part I Welcome to Adobe Photoshop CS4 Overview of the main types and characteristics of digital images Following are basic descriptions of digital image types and characteristics: n Bit depth. The higher an image’s bit depth, the more colors each of its pixels can be; therefore, the more colors and degrees of brightness the image can contain. n Bitmap (raster) and vector. A bitmap, or raster, image gets its detail from the number of pixels it contains.
Working with Digital Images Bit depth is measured in bits per channel (bpc): n 1 bit/channel. An image with a bit depth of 1 has pixels with only two possible values, black or white. A Bitmap mode image has one channel with pixels that can be either black or white. There is no 1 Bit/Channel option that can be selected in Photoshop, but Bitmap mode images are 1-bpc images. n 8 bits/channel. An image with a bit depth of 8 has 28, or 256, possible values per channel.
Part I Welcome to Adobe Photoshop CS4 Eight-bpc RGB images are sometimes called 24-bit images (8 bits x 3 channels = 24 bits of data for each pixel). This can be confusing. For example, sometimes 8-bpc RGB images are called 8-bit images and sometimes they are called 24-bit images. CAUTION Thirty-two-bpc HDR images can represent the entire dynamic range of the visible world, unlike the lower bit depths, which can represent only a portion of it.
Working with Digital Images Following are the steps to convert from 32-bpc HDR to 16- or 8-bpc: 1. Choose Image ➪ Mode ➪ 16 Bits/Channel or 8 Bits/Channel. 2. Make sure the Preview box is checked and choose one of the following four methods for adjusting the brightness and contrast in the image until the image’s appearance and tonal range meets your requirements: n Exposure and Gamma. Move the Exposure slider to adjust the gain, and move the Gamma (midtone) slider to adjust the contrast.
Part I Welcome to Adobe Photoshop CS4 Bitmap (raster) and vector A bitmap, or raster, image gets its detail from the number of pixels it contains, which is called resolution. Since they depend on the number of pixels for detail, bitmap images are said to be resolution-dependent. Resolution is commonly expressed in Photoshop as the number of pixels per inch (ppi). Choose Image ➪ Image Size to see the resolution of an image.
Working with Digital Images Images that are made up of some combination of solid colors, simple gradations between colors, distinct shapes, and lines can be constructed as vector images. Simple logos and cartoon-type illustrations often have these characteristics, but some complex illustrations do, too.
Part I Welcome to Adobe Photoshop CS4 The type of layer shown is a shape layer, a layer completely filled with a color (in this case, black) and that has a vector layer mask that hides part of the color on the layer, leaving visible what looks like a shape. White areas on a vector mask allow the color on the layer to be visible; gray on a vector mask hides the layer’s color. The layer name is “Shape Layer-Black,” and the vector layer mask is immediately to the left of the layer name.
Working with Digital Images Figure 1.5 shows a vector-only image with four colors. The layers are linked so that they resize together. Figure 1.6 shows a combination vector and bitmap image. The type layer contains vector information, the Star Shape Layer contains the star shape in the vector layer mask, and the Background layer contains a bitmap image. FIGURE 1.5 A vector-only image with four colors. Vector information is contained in the vector layer masks. FIGURE 1.
Part I Welcome to Adobe Photoshop CS4 While the vector parts of the image are still resolution-independent and can be resized with no worries, the image must have enough resolution to describe the detail in the bitmap photo. Printing an enlarged bitmap image that doesn’t have enough resolution to describe the detail in the enlarged size often results in a pixilated look, shown in Figure 1.7. CROSS-REF Part IV explains how to create vector paths, type, and shapes. FIGURE 1.
Working with Digital Images Color mode The color mode of an image specifies which basic set of colors is used to make up an image. You can specify the color mode in the Image ➪ Mode menu. Colors within most color modes are stored in color channels. You can view the channels in the Channels palette. The color modes available in Photoshop are: n RGB color mode. Red, Green, and Blue are used to make up the image’s color.
Part I Welcome to Adobe Photoshop CS4 FIGURE 1.10 CMYK mode channels FIGURE 1.11 Lab mode channels n Grayscale mode. Black, white, and shades of gray are used to make up the “colors” in an image (no hue is present). In 8-bpc images, there can be 256 brightness values. Grayscale images’ values can be measured in a range from 0 (black) to 255 (white) or with 0 percent–100 percent of black ink coverage. Grayscale mode (see Figure 1.12) can be used when preparing images to be printed with one color of ink.
Working with Digital Images n Duotone mode. In Duotone mode, one to four custom inks can be used to make up the colors in an image. Figure 1.14 shows Duotone-mode channels, options, and curves. A dutone can be used to add a color tint to a black-ink photo printed in a brochure that uses only black ink plus one other color. A quadtone with custom inks can give a rich and uniquely colored look to a photograph.
Part I Welcome to Adobe Photoshop CS4 The Duotone-mode images can be referred to as monotones, duotones, tritones, or quadtones. Their values are typically measured with 0%–100% of ink coverage. Duotone mode is used when two, three, or four custom ink colors (other than the typical CMYK combination) are used in printing.
Working with Digital Images n Multichannel mode. Multichannel mode uses only spot channels (see Figure 1.16), channels that store parts of an image that you want to print in custom-selected inks (sometimes called spot colors), such as inks from the Pantone color library. In Multichannel mode, you can put certain parts of an image on each spot channel and assign custom-selected inks to the spot channel.
Part I Welcome to Adobe Photoshop CS4 Before you begin working on an image, you can specify the color spaces (also called color profiles or gamuts) for various types of images, such as RGB, CMYK, Grayscale, and Spot Color. This enables Photoshop’s color management functions, which attempt to keep colors accurate across devices, such as a monitor, a desktop printer, and a printing press. To specify color spaces, choose Edit ➪ Color Settings (see Figure 1.17).
Working with Digital Images CROSS-REF More about color management is discussed in Chapter 23. File format Various destinations for an image, such as other software or a computer screen display, require certain file formats because of the software language or properties of the device. Some common file formats are JPEG and GIF, usually used for Web page display, and TIFF, often used for page layout programs and printing. The file formats supported by Photoshop CS4 are listed in Table 1.2.
Part I Welcome to Adobe Photoshop CS4 TABLE 1.2 (continued) Format Extension EPS with PICT Preview .eps EPS with TIFF Preview .eps Filmstrip .flm Google Earth 4 .kmz JPEG .jpg, .jpeg, .jpe JPEG 2000 .jpf, .jpx, .jp2, .j2c, .j2k, .jpc Kodak Photo CD .pcd Large Document Format .psb MacPaint .mpt, .mac OpenEXR .exr PCX .pcx PDF .pdf, .pdp Photoshop .psd, .pdd Photoshop DCS 1.0 and 2.0 .eps Photoshop Raw .raw PICT .pct, .pict PICT Resource .rsr Pixar .pxr PixelPaint .
Working with Digital Images Low versus high resolution Bitmap images, as opposed to vector-only images, depend on the number of pixels in the image to describe the image’s detail. In Photoshop, image resolution is measured in pixels per inch (ppi) and can be seen and changed in the Image Size dialog box (choose Image ➪ Image Size), shown in Figure 1.18. If an image does not have enough resolution for its purpose, it may look blurry or pixilated.
Part I Welcome to Adobe Photoshop CS4 CROSS-REF For more about image resolution and resizing, see Chapter 5. Getting Images into Photoshop It’s great to know a lot about Photoshop, and if you’ve read the previous sections in this chapter, you have already gained knowledge that, believe it or not, many Photoshop users have not taken the time to learn. But to apply that knowledge, you need to know how to get images from their sources onto your computer and ready to open in Photoshop.
Working with Digital Images FIGURE 1.19 USB connectors FIGURE 1.20 FireWire connectors FireWire You can also contact the manufacturer to find out what kind of cable you need for your camera model. The major manufacturers, like Canon and Nikon, have Web sites with lots of information, including downloadable camera operation manuals. You can also take the camera to an electronics store, such as Circuit City, for help finding the right cable.
Part I Welcome to Adobe Photoshop CS4 CROSS-REF Adobe Bridge provides a useful visual interface to find, open, and process files on your computer. Using Bridge is discussed in Chapter 3. FIGURE 1.21 An example of a file path from a camera’s memory card to the images: NO NAME ➪ DCIM ➪ 101CANON ➪ images After you connect your camera or memory card to your computer, you can use Adobe Bridge’s Photo Downloader by following these steps: 1. In Photoshop: Choose File ➪ Browse (opens Bridge). 2.
Working with Digital Images FIGURE 1.22 The Adobe Bridge Photo Downloader Scanners You can scan negatives, slides, and other transparencies with a film scanner, or you can scan prints with a flatbed scanner. Some film scanners will do batch scans, which can save loads of scanning time. If you have a lot of slides or negatives, you may also find reasonably priced services on the Web that offer mass film scanning.
Part I Welcome to Adobe Photoshop CS4 You can be confident that images for print will have enough resolution if they are scanned at 300ppi resolution or larger than their final printed size in inches. Images for on-screen display need to have 72ppi resolution at their final size in pixels. Web pages are often constrained to an 800 wide x 600 tall pixel area, so that should give you some idea of the pixel dimensions your images for the Web need to be. If in doubt, scan at a larger size.
Working with Digital Images There may also be a download button in the e-mail program, which may not give you an opportunity to choose a location on your computer. If you can’t choose a location, you will need to know where your computer auto-saves downloaded files or make a note of the image name and search your computer for it after it is downloaded.
Part I Welcome to Adobe Photoshop CS4 FIGURE 1.23 iMovie lets you capture and save a still frame by navigating to the frame within the movie clip and choosing Edit ➪ Create Still Frame, then File ➪ Save Frame. Typical steps to get video from a digital camcorder onto your computer include: 1. Make sure any recording media (MiniDV tape, MiniDVD disk) is in the camcorder. 2. Open Windows Movie Maker or iMovie. 3. Turn on the camcorder and make sure it is set to the video mode rather than the camera mode.
Working with Digital Images FIGURE 1.24 iMovie detects a connected video camera and lets you import the video by clicking the Import button. If these steps don’t work for your camcorder and media, keep the following tips in mind: n MiniDVD disks cannot be put into slot-loading DVD drives and require tray-loading DVD drives (which can be purchased inexpensively).
Part I Welcome to Adobe Photoshop CS4 Storing Digital Images It’s easy for digital images to accumulate to an unmanageable number, and storing and backing up images is often a concern. External hard drives are relatively inexpensive and offer large amounts of storage space. They can be used to regularly back up not only your images but also your entire internal hard drive.
