Photoshop cs5 by steve Johnson part 29 ppsx

ptg Chapter 8 Understanding Colors and Channels 181 The CMYK color mode is the color mode of paper and press. Printing presses (sometimes referred to as a 4-color press) convert an image's colors into percentages of CMYK (Cyan, Magenta, Yellow, and Black), which eventually become the color plates on the press. One at a time, the plates apply color to a sheet of paper, and when all 4 colors have been applied, the paper contains an image similar to the CMYK image created in Photoshop. The CMYK color mode can take an image from a computer monitor to a printed document. Before converting an image into the CMYK mode, however, it's important to understand that you will lose some color saturation during the conversion. The colors that will not print are defined as being out of gamut. To view the areas of an RGB image that will lose saturation values, click the View menu, and then click Gamut Warning. Photoshop will mask all the areas of the image that are out of gamut. Understanding the CMYK Color Mode Convert an Image to CMYK Color Open an image. Click the Image menu, point to Mode, and then click CMYK Color. Photoshop converts the image into the CMYK color mode. 2 1 CMYK color mode 1 See Also See “Using Curves and Color Adjustments” on page 200 for more information on adjusting the color of an image. From the Library of Wow! eBook ptg 182 Chapter 8 The Grayscale color mode utilizes an 8-bit pixel (8 on/off light switches) to generate 1 black, 1 white, and 254 shades of gray. Although scanning and working on old black and white images might seem the obvious reason to use the Grayscale color mode, the speed and power of Photoshop, combined with faster computer systems, has prompted most photo restorers to switch to the RGB color space because of its greater versatility and ability to generate millions of colors (or shades of gray). Yet despite the move to RGB, the Grayscale color mode is still used extensively with black and white images, where file size is a con- sideration (grayscale images are two-thirds smaller than RGB images), and when output to rag-style papers, such as newsprint, fail to produce the detailed information available with RGB. Understanding the Grayscale Color Mode Convert an Image to Grayscale Open an image. Click the Image menu, point to Mode, and then click Grayscale. The image is automatically converted into the Grayscale color mode. 2 1 Grayscale color mode 1 Did You Know? You can colorize a grayscale image. Convert the image into the RGB mode, and then select a color, brush, and brush size on the Options bar. The trick is to change the blending mode of the brush on the Options bar to Color. Then, as you paint on the image, the selected color will replace the original grays. Colorizing a Grayscale Image If you're planning on colorizing a grayscale image, you can increase your control of the image by creating a layer directly above the image layer, and painting in the new layer. Leave the blending mode of the brush at Normal and change the blending mode of the new layer to Color. When you paint, the color is applied and controlled in the new layer, and you have the additional option of using layer opacity to control the intensity of the effect. For Your Information From the Library of Wow! eBook ptg Chapter 8 Understanding Colors and Channels 183 Bitmap images consist of two colors: black and white. Bitmap images are sometimes referred to as 1-bit images. Think of a bitmap as a light switch with two positions, on and off. Each pixel in a bitmap image is either on or off, black or white. Because they are only 1 bit, the file size of a bitmap image is typically very small. Bitmap images have limited use, but often are employed for black and white ink drawings, line art, sketches, and for creating halftone screens. Understanding the Bitmap Color Mode Convert an Image to Bitmap Open an image. Click the Image menu, point to Mode, and then click Bitmap. IMPORTANT Before converting an image into a bitmap, it must first be in the Grayscale color mode. Enter a value for Output Resolution. Click the Use list arrow, and then select from the available options: ◆ 50% Threshold. Converts pixels with gray values above the middle gray level (128) to white and below to black. The result is a high-contrast, black-and-white image. ◆ Pattern Dither. Converts an image by organizing the gray levels into geometric patterns of black and white dots. ◆ Diffusion Dither. Converts pixels with gray values above the middle gray level (128) to white and below to black using an error- diffusion process. The result is a grainy, film-like texture. ◆ Halftone Screen. Simulates the effect of printing a grayscale image through a halftone screen. ◆ Custom Pattern. Simulates the effect of printing a grayscale image through a custom halftone screen. This method lets you apply a screen texture, such as a wood grain, to an image. Click OK. 5 4 3 2 1 5 3 4 Bitmap color mode 50% Threshold Diffusion Dither From the Library of Wow! eBook ptg 184 Chapter 8 The Indexed Color mode gives you two advantages. You can create images as small as grayscale (8-bit pixels), and you get color instead of shades of gray. Its small file size and ability to generate color make it a winning color mode for images displayed on web pages, as well as graphics used in computer-generated presentations. Its one drawback is the number of colors generated; Indexed Color images generate a maximum of 256 colors (the same number as the steps of gray in a grayscale image). The good news is that you get to choose the colors. When you convert an image into the Indexed Color mode, Photoshop creates a color lookup table (CLUT) to store the image's color informa- tion. When a color in the image cannot be found in the lookup table, Photoshop substitutes the closest available color. Understanding the Indexed Color Mode Convert an Image to Indexed Color Open an image. Click the Image menu, point to Mode, and then click Indexed Color. Select from the following Indexed Color Mode options: ◆ Palette. Click the list arrow to choose from the available color panels, or click Custom and create your own palette. ◆ Colors. Select the number of colors for the lookup table (9 to 256). ◆ Forced. Force the lookup table to hold specific colors. Black and White adds a pure black and a pure white to the color table; Primaries adds red, green, blue, cyan, magenta, yellow, black, and white; Web adds the 216 web-safe colors; and Custom allows you to specify your own colors. ◆ Transparency. Select the check box to preserve transparent areas of the image (if there are no transparent areas, this option is disabled). 3 2 1 3 From the Library of Wow! eBook ptg Chapter 8 Understanding Colors and Channels 185 Select from the following options: ◆ Matte. Click the list arrow to fill transparent areas of the original image with a specific color. ◆ Dither. Click the list arrow, and then select a pixel-mixing (dither) scheme. Dithering helps transitional areas of the image (shadows, light to dark) appear more natural. ◆ Amount. If the Dither option is selected, the Amount instructs Photoshop how much color information to use in the dithering process (0% to 100%). ◆ Preserve Exact Colors. Select the check box to hold exact color measurements in the lookup table. Click OK. 5 4 5 4 Indexed color image Indexed color mode From the Library of Wow! eBook ptg 186 Chapter 8 The Lab color mode is an old color measuring system. Created in France, its purpose was to measure color based on visual perception. Since personal computers had not been created at that time, the Lab mode is not based on a particular computer or operating system, and so Lab color is device independent. The Lab mode measures color using a lightness channel, an "a" channel (red to green), and a "b" chan- nel (blue to yellow). Lab Color works well for editing images obtained from Photo CDs or DVDs, moving images between operating systems (Photoshop Mac to Photoshop Win), and for printing color images to PostScript Level 2 or 3 devices. Because of its ability to separate the gray tones of an image into an individual channel (lightness), the Lab color mode is excellent for sharpening, or increasing the contrast of an image without changing its colors. Just convert the original RGB image to Lab color, select the Lightness channel, and perform sharpening or Levels and Curves adjustments directly to the channel. Understanding the Lab Color Mode Convert an Image to Lab Color Open an image. Click the Image menu, point to Mode, and then click Lab Color. Photoshop converts the image into the Lab color mode. 2 1 1 Lab color mode Did You Know? You can use the Lab color mode to archive RGB color images. Since the Lab color space is device- independent, and RGB is device- dependent, archiving RGB images in the Lab color mode stabilizes the image's color information and insures color accuracy, no matter what editing application is used. From the Library of Wow! eBook . Indexed Color mode, Photoshop creates a color lookup table (CLUT) to store the image's color informa- tion. When a color in the image cannot be found in the lookup table, Photoshop substitutes. editing images obtained from Photo CDs or DVDs, moving images between operating systems (Photoshop Mac to Photoshop Win), and for printing color images to PostScript Level 2 or 3 devices. Because. Image to CMYK Color Open an image. Click the Image menu, point to Mode, and then click CMYK Color. Photoshop converts the image into the CMYK color mode. 2 1 CMYK color mode 1 See Also See “Using