Adobe Photoshop CS3 Manual de usuario descargar pdf (Pagina 195)

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101

PHOTOSHOP CS3

User Guide

188

Invert colors

The Invert command inverts the colors in an image. You can use this command as part of the process of making an

edge mask to apply sharpening and other adjustments to selected areas of an image.

Note: Becausecolorprintfilmcontainsanorangemaskinitsbase,theInvertcommandcannotmakeaccuratepositive

images from scanned color negatives. Be sure to use the proper settings for color negatives when scanning film.

When you invert an image, the brightness value of each pixel in the channels is converted to the inverse value on the

256-step color-values scale. For example, a pixel in a positive image with a value of 255 is changed to 0, and a pixel

with a value of 5 is changed to 250.

Do one of the following:

• Choose Image > Adjustments > Invert.

• Choose Layer > New Adjustment Layer > Invert. Click OK in the New Layer dialog box.

Create a two-value black and white image

The Threshold command converts grayscale or color images to high-contrast, black-and-white images. You can

specify a certain level as a threshold. All pixels lighter than the threshold are converted to white; all pixels darker are

converted to black.

1 Do one of the following:

• Choose Image > Adjustments > Threshold.

• ChooseLayer>NewAdjustmentLayer>Threshold.ClickOKintheNewLayerdialogbox.TheThresholddialog

box displays a histogram of the luminance levels of the pixels in the current selection.

2 Drag the slider below the histogram until the threshold level you want appears at the top of the dialog box, and

click OK. As you drag, the image changes to reflect the new threshold setting.

Posterize an image

The Posterize command lets you specify the number of tonal levels (or brightness values) for each channel in an

image and then maps pixels to the closest matching level. For example, choosing two tonal levels in an RGB image

gives six colors: two for red, two for green, and two for blue.

This command is useful for creating special effects, such as large, flat areas in a photograph. Its effects are most

evident when you reduce the number of gray levels in a grayscale image, but it also produces interesting effects in

color images.

If you want a specific number of colors in your image, convert the image to grayscale and specify the number of levels

youwant.Thenconverttheimagebacktothepreviouscolor mode, and replace the various gray tones with the colors

you want.

1 Choose Image > Adjustments > Posterize.

2 Enter the number of tonal levels you want, and click OK.

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