Noise filters (Photoshop)

The Noise filters add or remove noise, or pixels with randomly distributed color levels. This helps to blend a selection into the surrounding pixels. Noise filters can create unusual textures or remove problem areas, such as dust and scratches, from an image.

Add Noise

Applies random pixels to an image, simulating the effect of shooting pictures on high-speed film. The Add Noise filter can also be used to reduce banding in feathered selections or graduated fills or to give a more realistic look to heavily retouched areas. Options include noise distribution: Uniform distributes color values of noise using random numbers between 0 and plus or minus the specified value for a subtle effect; Gaussian distributes color values of noise along a bell-shaped curve for a speckled effect. The Monochromatic option applies the filter to only the tonal elements in the image without changing the colors.

Despeckle

Detects the edges in an image (areas where significant color changes occur) and blurs all of the selection except those edges. This blur-ring removes noise while preserving detail.

Dust & Scratches

Reduces noise by changing dissimilar pixels. To achieve a balance between sharpening the image and hiding defects, try various combinations of radius and threshold settings. Or apply the filter on selected areas in the image.

To use the Dust & Scratches filter:

1. Choose Filter > Noise > Dust & Scratches.
2. If necessary, adjust the preview zoom ratio until the area containing noise is visible.
3. Drag the Threshold slider left to 0 to turn off the value, so that all pixels in the selection or image can be examined.

The Threshold determines how different the pixels' values should be before they are eliminated.

Note: The Threshold slider gives greater control for values between 0 and 128--the most common range for images--than for values between 128 and 255.

4. Drag the Radius slider left or right, or enter a value in the text box from 1 to 16 pixels. The radius determines how far the filter searches for differences among pixels.

Adjusting the radius makes the image blurry. Stop at the smallest value that eliminates the defects.

5. Increase the threshold gradually by entering a value or by dragging the slider to the highest value possible that eliminates defects.

Median

Reduces noise in an image by blending the brightness of pixels within a selection. The filter searches the radius of a pixel selection for pixels of similar brightness, discarding pixels that differ too much from adjacent pixels, and replaces the center pixel with the median brightness value of the searched pixels. This filter is useful for eliminating or reducing the effect of motion on an image.