The Median filter noise reduction technique (covered in the previous article) works well with images that have primarily luminance noise. However, it does not work as well with images that have color noise. Luckily, the technique can be modified by adding one additional layer that will handle color noise.
Figure 1 shows an image of a doll. A 100% crop of the image reveals a problem with luminance and color noise (see Figure 2). In this image, the color noise is particularly noticeable as blue specks.
The Reduce Noise filter offers another option for dealing with noise. One of the advantages of this filter is its ease of use due to the fact that both luminance and color noise can be handled by the same filter.
Figure 14 shows an image that was shot with a high ISO. A 100% crop of the image reveals the resultant noise (see Figure 15). The Noise Reduction filter will be used to improve the noise problem in this image.
Next, the Reduce Noise filer is launched (choose Filter/Noise/Reduce Noise). The Reduce Noise dialog box appears as seen in Figure 17. In the basic mode, there are five controls:
A couple of things should be kept in mind when using this filter. First, the Strength and Preserve Details settings work against each other. Higher Strength settings will remove more noise, but it will also remove more detail. Higher Preserve Details settings will preserve more detail, but it will also preserve more noise. It is necessary to play with these two settings to find the best combination that reduces the noise but leaves as much detail as possible. Second, it may be best to leave the Sharpen Details setting at 0. That way, the noise reduction and sharpening can be handled independently.
This particular image had quite a bit of luminance noise, so the Strength setting was set very high. Conversely, the image does not have much detail; thus, the Preserve Details setting was set very low. The Reduce Color Noise was set to a moderate level. Lastly, the Sharpen details was set to zero and the Remove JPEG Artifact was turned off.
Figures 18 and 20 show crops of the image before the noise removal steps. Figures 19 and 21 show the same crops after these steps.
My opinion is that this technique is not as thorough in removing noise as the previous two techniques. However, it is quick and easy.
The noise reduction on this image was done with the Basic Noise Reduction Dialogue Box. Clicking the Advanced option brings up more alternatives (see Figure 22). Once in the Advanced mode, moving to the Per Channel tab allows the Strength and Preserve Details controls to be applied to each channel independently.
This ability is of value when there are different amounts of noise in the three channels. However, this option will not be used with the current image.
If one wants the maximum amount of detail, the edge technique can be used to add more detail back into the image.