Clear The Noise From RGB Channels

Noise Reduction On RGB Channels

Most digital images are a composite of information held in Red, Green, and Blue channels. You can use the RGB channels to help you to see where exactly the noise is causing the most trouble in your picture. If you don’t have the channels window open in Photoshop, click Window and Channels.                                   

                                     

It’s incredibly noisy, and genuinely so: I accidentally had the ISO cranked up on a bright day!

Assess the Image: Evaluate Noise on the RGB Channels

Most digital images are a composite of information held in Red, Green, and Blue channels. You can use the RGB channels to help you to see where exactly the noise is causing the most trouble in your picture. If you don’t have the channels window open in Photoshop, click Window and Channels.   

                     

     

You’ll see your picture broken down into three channels: Red, Green and Blue. You want to evaluate each channel to look for noise. Here is each channel for my sample image:

Red Channel

                     

The red channel is incredibly noisy, pretty much across the whole image.

Green Channel

                          

Green isn’t so bad apart from the trees and riverbank.

Blue Channel

                             

Blue isn’t bad either; mostly the noise is in the water but you can’t see that as much due to the nature of the image.

Apply Noise Reduction on the RGB Channels

You can apply a filter on a particular channel. Taking my Red channel, which was the worst for visible noise, I selected the sky and applied a Surface Blurfrom the Filters list.

                      

Surface blur will take larger areas of the same colour and blur it without ruining your edges too much, so you can try applying it to the whole picture. If it’s a particularly noisy image, like mine, applying this strength of blur to the whole image would soften the details considerably, despite only being on one channel.

So, rather than applying the blur filter to the particular channel, let's use a noise reduction filter instead. Hit Filter > Noise > Reduce Noise:

                        

You’ll see you can check each channel for noise here too. The dialogue will allow you to click on the actual image to see a particular section in the preview. You also have the option to Preserve Details, so you can experiment with moving the sliders to see which works best. 

First, select the channel with the most noise. Now reduce noise using this process:

1. Move the Strength slider to the right, past the level where noise reduction starts to detrimentally effect the image. The image will start to look smudged.
2. Then move the slider slowly to the left, or use the up and down arrow keys, to gently reduce the filter Strength until you return to an acceptable image quality. 
3. Repeat this process with the Preserve Details slider to fine tune the filter. 

Then do the same steps for the remaining two channels.