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Working with Color in Photoshop

About the different color modes (Photoshop)

    Color models describe colors numerically. There are different methods of describing colors numerically, and a color mode determines which method or set of numbers to use to display and print an image. Photoshop bases its color modes on the color models that are useful for images used in publishing. You can choose from RGB (red, green, blue); CMYK (cyan, magenta, yellow, black); Lab Color (based on CIE L*a*b*), and Grayscale. Photoshop also includes modes for specialized color output such as Indexed Color and Duotone.

    Note: ImageReady only uses the RGB mode to work with images, since its documents are primarily intended for the Web. For more information about color models,

    In addition to determining the number of colors that can be displayed in an image, color modes affect the number of channels and the file size of an image.

 

Adjusting the monitor display

Although the RGB color model used by computer monitors is capable of displaying much of the visible spectrum, the video system sending data to a given monitor often limits how many colors can be displayed at once. By understanding how color data is measured in digital files and on-screen, you can better adjust color display settings to offset the limitations of your video system. For critical work, your monitor should be calibrated and characterized for use in a color management system. At the very least, your monitor should be calibrated to display colors as accurately as possible. For more information on calibrating your monitor and creating a display profile,

 

Channels and bit depth (Photoshop)

A working knowledge of color channels and bit depth is key to understanding how Photoshop stores and displays color information in images.


Converting between color modes (Photoshop)

Photoshop lets you change an image from its original mode (source mode) to a different mode (target mode). When you choose a different color mode for an image, you permanently change the color values in the image. For example, when you convert an RGB image to CMYK mode, RGB color values outside the CMYK gamut (defined by the CMYK working space setting in the Color Settings dialog box) are adjusted to fall within gamut. As a result, some image data may be lost and will not be recovered if you were to convert the image from CMYK back to RGB.

 

Converting images to Bitmap mode (Photoshop)

Converting an image to Bitmap mode reduces the image to two colors, greatly simplifying the color information in the image and reducing its file size.

 

Converting to indexed color (Photoshop)

Converting to indexed color reduces the number of colors in the image to at most 256--the standard number of colors supported by the GIF and PNG-8 formats and many multimedia applications. This conversion reduces file size by deleting color information from the image.

To convert to indexed color, you must start with an image that is 8 bits per channel and either grayscale or RGB.

To convert a grayscale or RGB image to indexed color:

  1. Choose Image > Mode > Indexed Color.

    Note: All visible layers will be flattened; any hidden layers will be discarded.

    For grayscale images, the conversion happens automatically. For RGB images, the Indexed Color dialog box appears.

  2. Select Preview in the Indexed Color dialog box to display a preview of the changes.
  3. Specify conversion options.

 

Conversion options for indexed-color images (Photoshop)

When converting an RGB image to indexed color, you can specify a number of conversion options in the Indexed Color dialog box.

 

Customizing indexed color tables (Photoshop)

The Color Table command lets you make changes to the color table of an indexed-color image. These customization features are particularly useful with pseudocolor images--images displaying variations in gray levels with color rather than shades of gray, often used in scientific and medical applications. However, customizing the color table can also produce special effects with indexed-color images that have a limited number of colors.

Note: To shift colors simply in a pseudocolor image, choose Image > Adjustments, and use the color adjustment commands in the submenu. For a summary description of these commands,

 

Using the Adobe Color Picker

The Adobe Color Picker lets you select a color by choosing from a color spectrum or by defining colors numerically. The Adobe Color Picker can be used for setting the foreground color, background color, and text color. In Photoshop, it is also used for setting target colors in some color and tonal adjustment commands, the stop colors in the Gradient Editor, the filter color in the Photo Filter command, and the color in a fill layer, certain layer styles, and shape layers.

When a color is selected in the Adobe Color Picker, the numeric values for HSB, RGB, Lab, CMYK, and hexadecimal numbers are simultaneously displayed. This is useful for viewing how a color is described by the different color modes.

 

Using other color pickers

In addition to the default Adobe Color Picker, you can use the built-in color pickers on your system or a plug-in color picker to select colors. Any plug-in color pickers you install appear under Color Picker in the General section of the Preferences dialog box. For information on installing and using a plug-in color picker, see the documentation that came with the plug-in.

To use the Windows Color Picker (Windows):

  1. Choose Edit > Preferences > General.
  2. Choose Windows from the Color Picker menu, and click OK.

    For more information, see your Windows documentation.

To use the Apple Color Picker (Mac OS):

  1. Do one of the following:
    • (Photoshop) Choose Photoshop > Preferences > General.
    • (ImageReady) Choose ImageReady > Preferences > General.
  2. For Color Picker, do one of the following:
    • (Photoshop) Choose Apple and click OK.
    • (ImageReady) Choose System, and click OK.

    For more information, see your Mac OS documentation.

To return to the Adobe Color Picker after using another color picker:

  1. Do one of the following:
    • In Windows, choose Edit > Preferences > General.
    • (Photoshop) In Mac OS, choose Photoshop > Preferences > General.
    • (ImageReady) In Mac OS, choose ImageReady > Preferences > General.
  2. Choose Adobe from the Color Picker menu, and click OK.
     
Using the color wheel

When working with color, there are numerous ways to achieve similar results in color balance. It's useful to consider the type of image you have and the effect you want to produce. If you're new to adjusting color components, it helps to keep a diagram of the standard color wheel on hand. You can use the color wheel to predict how a change in one color component affects other colors and also how changes translate between RGB and CMYK color models.

    Color wheel R. Red Y. Yellow G. Green C. Cyan B. Blue M. Magenta

    For example, you can decrease the amount of any color in an image by increasing the amount of its opposite on the color wheel--and vice versa. Colors that lie opposite each other on the standard color wheel are known as complementary colors. Similarly, you can increase and decrease a color by adjusting the two adjacent colors on the wheel, or even by adjusting the two colors adjacent to its opposite.

    In a CMYK image, you can decrease magenta either by decreasing the amount of magenta or by increasing its complement (by adding cyan and yellow). You can even combine these two corrections, minimizing their effect on overall lightness. In an RGB image, you can decrease magenta by removing red and blue or by adding green. All of these adjustments result in an overall color balance containing less magenta.

 

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