Adobe Photoshop CS3 Manual de usuario descargar pdf (Pagina 214)

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PHOTOSHOP CS3

User Guide

207

Reduce image noise and JPEG artifacts

Image noise appears as random extraneous pixels that aren’t part of the image detail. Noise can be caused by photo-

graphing with a high ISO setting on a digital camera, underexposure, or shooting in a dark area with a long shutter

speed. Low-end consumer cameras usually exhibit more image noise than high-end cameras. Scanned images may

have image noise caused by the scanning sensor. Often, the film’s grain pattern appears in the scanned image.

Image noise can appear in two forms: luminance (grayscale) noise, which makes an image look grainy or patchy, and

color noise, which is usually visible as colored artifacts in the image.

Luminance noise may be more pronounced in one channel of the image, usually the blue channel. You can adjust the

noiseforeachchannelseparatelyinAdvancedmode.Beforeopeningthefilter,examineeachchannelinyourimage

separatelytoseeifnoiseisprevalentinonechannel.Youpreservemoreimagedetailbycorrectingonechannelrather

than making an overall correction to all channels.

1 Choose Filter > Noise > Reduce Noise.

2 Zoom in on the preview image to get a better view of image noise.

3 Set options:

Strength Controls the amount of luminance noise reduction applied to all image channels.

Preserve Details Preserves edges and image details such as hair or texture objects. A value of 100 preserves the most

imagedetail,butreducesluminancenoisetheleast.BalancetheStrengthandPreserveDetailscontrolstofine-tune

noise reduction.

Reduce Color Noise Removes random color pixels. A higher value reduces more color noise.

Sharpen Details Sharpens the image. Removing noise reduces image sharpness. Use the sharpening control in the

dialog box or use one of the other Photoshop sharpening filters later to restore sharpness.

Remove JPEG Artifacts Removes blocky image artifacts and halos caused by saving a image using a low JPEG quality

setting.

4 If luminance noise is more prevalent in one or two color channels, click the Advanced button and then choose the

color channel from the Channel menu. Use the Strength and Preserve Details controls to reduce noise in that

channel.

Adjusting image sharpness and blur

Sharpen images

Sharpening enhances the definition of edges in an image. Whether your images come from a digital camera or a

scanner, most images can benefit from sharpening. The degree of sharpening needed varies depending on the quality

of the digital camera or scanner. Keep in mind that sharpening cannot correct a severely blurred image.

Notes and tips about sharpening:

• Sharpen your image on a separate layer so that you can resharpen it later if you need to output it to a different

medium.

• If you sharpen your image on a separate layer, set the layer’s blending mode to Luminance to avoid color shifts

along edges.

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