Adobe Photoshop CC 2014 v.14.xx - Manual (Page 212)

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Palette Type
Convert a color photo to Grayscale mode
1. Open the photo you want to convert to black-and-white.
2. Choose Image > Mode > Grayscale.
3. Click Discard. Photoshop converts the colors in the image to black, white, and shades of gray.
The technique above minimizes file size but discards color information and can convert adjacent colors to the exact same shade of
gray. Using a Black & White adjustment layer increases file size but retains color information, letting you map colors to shades of gray.
Convert a Bitmap mode image to Grayscale mode
You can convert a Bitmap mode image to Grayscale mode in order to edit it. Keep in mind that a Bitmap mode image edited in Grayscale mode
may not look the same when you convert it back to Bitmap mode. For example, suppose a pixel that is black in Bitmap mode is edited to a shade
of gray in Grayscale mode. When the image is converted back to Bitmap mode, that pixel is rendered as white if its gray value is above the middle
gray value of 128.
1. Choose Image > Mode > Grayscale.
2. Enter a value between 1 and 16 for the size ratio.
The size ratio is the factor for scaling down the image. For example, to reduce a grayscale image by 50%, enter 2 for the size ratio. If you
enter a number greater than 1, the program averages multiple pixels in the Bitmap mode image to produce a single pixel in the grayscale
image. This process lets you generate multiple shades of gray from an image scanned on a 1-bit scanner.
Convert a grayscale or RGB image to indexed color
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 in either Grayscale or RGB mode.
1. Choose Image > Mode > Indexed Color.
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
When converting an RGB image to indexed color, you can specify a number of conversion options in the Indexed Color dialog box.
A number of palette types are available for converting an image to indexed color. For the Perceptual, Selective, and Adaptive
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