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Changing Color Modes

Before converting your file to a different color mode, it's a good idea to save a "master" version of your photo first. That way, no matter what changes you make to your image, you always have an untouched backup version, just in case.

To convert an image to grayscale:

  1. From the Image menu, select Mode > Grayscale ( Figure 3.5 ).

    Figure 3.5 Choose Image > Mode > Grayscale to convert an RGB image to grayscale. A grayscale image is only about 1/3 the size of an RGB image.

    A message appears asking "Discard color information?"
  2. Click OK ( Figure 3.6 ).

    Figure 3.6 In order to convert from RGB to grayscale, you will discard the color information. Before you convert an image to grayscale, you may want to save a separate version to preserve the colors in the original image file.

    The conversion discards all color information, resulting in an image with up to 256 shades of gray. (See the color plate section of this book for a full-color example.)

To convert an image to bitmap:

  1. From the Image menu, select Mode > Bitmap ( Figure 3.7 ).

    Figure 3.7 Choose Image > Mode > Bitmap to convert an image to bitmap (black and white) mode.

  2. Click OK to convert the image to grayscale ( Figure 3.8 ).

    Figure 3.8 Before converting to bitmap mode, your image is converted to grayscale.

    The Bitmap dialog box appears ( Figure 3.9 ).

    Figure 3.9 The Bitmap dialog box.

  3. If desired, enter a value for the output resolution. The default value is the current resolution of the image, which is usually fine for most purposes, and need not be changed during this conversion.
  4. From the Use pop-up menu, choose from one of the following three conversion methods to complete the bitmap conversion:
    • 50% Threshold converts pixels above medium gray to white, and below medium gray to black, resulting in a high-contrast image ( Figure 3.10 ).

      Figure 3.10 50% Threshold results in a high-contrast image.

    • Pattern Dither converts areas of gray into geometric patterns ( Figure 3.11 ).

      Figure 3.11 Pattern Dither creates geometric patterns based on areas of gray.

    • Diffusion Dither results in a grainy, graphic look ( Figure 3.12 ).

      Figure 3.12 Diffusion Dither results in a grainy, posterized look.

  5. Click OK to convert the image to bitmap mode.

To convert an image to indexed color:

  1. From the Image menu, select Mode > Indexed Color ( Figure 3.13 ).

    Figure 3.13 Choose Image > Mode > Indexed Color to convert an RGB image to indexed color.

    The Indexed Color dialog box appears.
  2. Choose Palette, Dither, and other options displayed in the dialog box ( Figure 3.14 ).

    Figure 3.14 The Indexed Color dialog box includes options for choosing colors, palettes, and dithering. This figure shows the dialog box on a Macintosh.

    Palette options allow you to choose the best color palette, taking into account where the image will ultimately be viewed. See the sidebar "Indexed Color Palette Options" for a summary of the different Palette options. The Forced option lets you lock in specific colors so that they are not changed in the conversion process. You can choose to lock in Black and White, which is particularly useful if you have a large area of white or black in the background, as well as Primaries (white, red, green, blue, cyan, magenta, yellow, and black). Choosing the Forced Web option protects all 216 "Web-safe" colors in the palette from being altered.
  3. Click OK to confirm your choices.

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