Shooting at high ISO can result in noise. Most of the time noise both color and luminance are found at dark areas of the photos. Applying noise reduction to the photos will also result in reduction of details. I've devised a method in selectively reducing noise on my photos shot at high ISO. Below is step by step guide to my selective noise reduction work flow on photoshop. (Click on the images to view full size)
1. Open the file
2. Create a duplicate layer of the file
3. Apply Noise reduction to the entire photo. You may use any noise reduction filter you like. I prefer the Reduce Noise Filter.
4. Apply desired amount on the noise reduction. Since my photo has a lot of visible chroma noise on the dark areas and contains visible luminance noise I choose to put the amount to full. I can adjust the amount of noise reduction on the dark areas later.
5. Since there are still some visible chroma noise in the photo I applied some blur to further reduce the visibility of the chroma noise. If by this point your photos are already free of luminance and chroma noise you can skip this step.
6. I picked smart blur to further reduce the chroma noise.
7. After applying the blur I selected everything on the photo and copied it.
8. I created a layer mask on the cleaned image
9. Went to the channels tab and pasted the copied image on the alpha channel tab.
10. After pasting the photo on the alpha channel I then inverted the alpha channel. The invert command is located on the menu Image>Adjustement>Invert
11. If by this point the photo is still a bit blurry you can select the alpha channel of the clean layer and adjust the levels. I usually drag the middle button to the right to increase the darkness of the midtones thus reducing the visibility of the clean image on the final image.
12. Save file and that is it.
For comparison I have attached the before and after image of the file
Before
100% crop
After
100% Crop
