If you have minor defects in your picture, some kind of noise or grains, Photoshop has a few filters, called Noise filters, to help you get rid of this problem.
1. Add Noise
This filter simulates the effect of shooting pictures on high-speed film. The effect is achieved by applying random pixels to an image. You can also use this filter to reduce banding in feathered selections or graduated fills or to give a more realistic look to heavily retouched areas.
To use it, open Filter>Noise>Add Noise, where you'll find the following settings:
Amount - determines the amount of the added noise (I used 2.5).
Distribution - can be Uniform and Gaussian. The first one distributes color values of noise using random numbers between 0 and plus or minus the specified value, so a subtle effect is created. The latter distributes color values of noise along a bell-shaped curve, creating a speckled effect (I applied the Uniform).
Monochromatic - if checked, applies the filter to only the tonal elements in the image without changing the colors (I used unchecked).
And here is my first beauty:
2. Despeckle
The filter is used to get rid of grain. It functions like the Unsharp Mask filter with a maximum value of 5. That means it slightly smudges the areas of homogeneous color and does not affect the contrast edges.
So, open the image and go to Filter>Noise>Despeckle. As the filter has no settings, you'll get something lie this:
3. Dust & Scratches
This filter removes the monochrome noise as well as scratches and traces of dust.
Start from opening the image. Select Filter>Texture>Diffuse. You'll see the following settings:
Radius - sets the radius of the filter (I used 1).
Threshold - specifies the threshold, over which the filter starts to operate interpolating the neigbouring pixels ( I set it to 1).
And this is what I got:
4. Median
This filter is used to get rid of color noise. It averages the colors of pixels lying within the set radius. At the same time, it ignores those pixels that differ radically from the average color in the circle. This way only the areas of comparatively uniform color get averaged, and the contrast edges remain intact.
Having opened the image, select Filter>Noise>Median. There is only one parameter to be set there:
Radius - determines the radius for the averaging of pixels (I used 1).
Look at what I got:
5. Reduce Noise
The filter reduces noise, but preserves edges due to the user setting that affects the overall image or individual channels.
You can get to this filter though Filter>Noise>Reduce Noise. These are its settings:
Strength - determines the amount of luminance noise reduction applied to all image channels (I used 8).
Preserve Details - preserves edges and image details such as hair or texture objects. The higher the value (100 is highest), the more image detail is preserved, but the less luminance noise is reduced. (15% is how much I used).
Reduce Color Noise - Removes random color pixels. A higher value reduces more color noise ( I set it to 40%).
Sharpen Details - Removing noise reduces image sharpness. This option is there to sharpen it back. Use the sharpening control in the dialog box ( I used 30%).
Remove JPEG Artifacts - Removes blocky image artifacts and halos caused by saving an image using a low JPEG quality setting.
Advanced button - lets you select between color channels. If luminance noise is more prevalent in one or two color channels, you can click this button and then choose the color channel from the Channel menu. Use the Strength and Preserve Details controls to reduce noise in that channel.
Settings - you can save/load your settings here for later use.
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