Adobe Photoshop CS3 Uživatelský manuál stáhnout pdf (Strana 122)

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PHOTOSHOP CS3

User Guide

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Pattern Dither conversion method, and Diffusion Dither conversion method

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

editedinGrayscalemodemaynotlookthesamewhenyouconvertitbacktoBitmapmode.Forexample,supposea

pixelthatisblackinBitmapmodeiseditedtoashadeofgrayinGrayscalemode.Whentheimageisconvertedback

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

toproduceasinglepixelinthegrayscaleimage.Thisprocessletsyougeneratemultipleshadesofgrayfromanimage

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.

Toconverttoindexedcolor,youmuststartwithanimagethatis8bitsperchannelandineitherGrayscaleorRGBmode.

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

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

Color dialog box.

Palette Type A number of palette types are available for converting an image to indexed color. For the Perceptual,

Selective,andAdaptiveoptions,youcanchooseusingalocalpalettebasedonthecurrentimage’scolors.Theseare

the available palette types:

• Exact Creates a palette using the exact colors appearing in the RGB image—an option available only if the image

uses 256 or fewer colors. Because the image’s palette contains all colors in the image, there is no dithering.

• System (Mac OS) Uses the Mac OS default 8-bit palette, which is based on a uniform sampling of RGB colors.

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