Digital images taken in certain illumination and camera setting conditions will present a certain amount of digital noise (in the frame noise appears as annoying red, green and blue blocks). If the amount of digital noise in a picture is too much, it will ruin that particular image.
In order to reduce digital noise from the source, when taking a picture, use the lowest available ISO setting in the camera. But there are times when a higher ISO value is required (images taken in low light). In order to maintain the aspect of the picture, but remove the noise, the Photoshop CS2 introduced a new filter, Reduce Noise. This filter can be found in the Filter>Noise menu, It is a powerful tool that reduces noise from grainy images (beware! because it only reduces noise, and does not remove it entirely).
If you take pictures in the RAW file format, use the Camera RAW plug-in to modify the amount of noise.
If you take pictures in different file formats other than RAW, use the Reduce Noise filter.
In the Reduce Noise dialog box there are several sliders. To prevent interference with the actual noise reduction, move the Preserve Details and Sharpen Details to the far left part of the slider.
Modify the Reduce Color Noise sliders for all three colors (red, green and blue) to the right until the wanted result in color noise reduction is visible. Modify the Sharpen Details slider, with 1% at a time until the color noise is back; at this point, back up with 1%.
Use the Preserve Detail slider until the proportion between the details in the image and the luminance noise is according to your needs. Certain non visible elements in the picture can be made seen using this slider after the noise reduction and the sharpening have been performed.
If the amount of noise in one color channel is far greater than others, use the Advanced settings of the Reduce Noise filter, by clicking on the Advanced button which can be found near the top of the dialog box. In the new window opened, modify individually each color channel reduce noise settings, until the desired effect on the image is attained. It is important to have checked the Remove JPEG Artifact check box if the images you save under the JPEG file format suffers from visible problems due to JPEG compression.
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