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Noise Reduction

When I photograph birds and wildlife, I often use ISO 400 or even 800. Even though the recent Canon cameras are pretty good at high ISO, there is always some noise, in particular in the smooth, out of focus areas. It is not a problem: with Photoshop, it is quite easy to reduce the noise, and I've made excellent print even from photos taken at very high sensitivities. Remember that, while it is possible to reduce the noise, it is not possible to correct the blur created by an excessively slow shutter speed: thus, don't hesitate to use high ISO when it is necessary.

 

Noise reduction with Photoshop CS3

Photoshop CS3 has a powerful noise reduction function that reduces effectively the "grain", keeping as much detail as possible. To open the NR window, click on the menu Filter > Noise > Reduce Noise. You can choose between a "Basic" and an "Advanced" interface; I always use the Basic option, since it is easier to use and faster, and it has all the controls that I need. On the left side of the window there is a large preview; in the right side there are four sliders.

Strength and Preserve Detail work together to determine the intensity of luminance noise reduction. I recommend to set both of them on a high value (I often use Strength 9 and Preserve Detail 90%). Remember that reducing luminance noise led to a more or less pronounced loss of detail: don't use an excessive reduction!

Reduce Color Noise determine the intensity of color noise reduction. The color noise is the most annoying type of noise, but it can be reduced very effectively without any loss detail; the only downside is a diminution of color accuracy (the colors become less vivid and saturated). Depending by the image, I suggest to use a value between 10 and 30.

Sharpen Details allows to apply some sharpening to the image; I suggest to avoid it (set the slider on 0%); it is better to use the much more sophisticated Smart Sharpen. The checkbox Reduce JPEG Artifacts is useful only with images that had been saved with an excessive JPEG compression; since I always use RAW, I let this checkbox deselected.

The Reduce Noise window is an useful tool, but you should learn to use it properly. A common error is to apply an excessive noise reduction; the resulting image is noise free but it has lost a lot of detail and it has a "plastic", artificial look. I am quite "conservative" with noise reduction; it is better to leave a little of noise that to get an over processed image. 

 

Noise reduction workflow

Canon EOS 20D, Canon EF 600mm f/4 L IS USM, Canon 1.4x TC, 1/4000 f/5.6, iso 400, handheld. Captive (Racconigi, Italy).

Even though it is possible to apply to noise reduction on the entire photo, I prefer to use a more advanced technique to preserve the detail of the subject and to get a cleaner image. With the Layer Mask, it is possible to apply the noise reduction only on the background, or to apply different levels of noise reduction on the subject and on the background.

This is a crop from the previous photo, without any adjustment other than the basic enhancements of brigthness and contrast. The photo has been taken at ISO 400 and it was slightly underexposed (when I photograph a white subject, I often set the expsure compesation on -0.3 to preserve the detail into highlights), so there is a little of noise, in particular in the out of focus background.

In the second crop, I applied a slight noise reduction on the entire image (Strenght 9, Preserve Detail 90%, Reduce Color Noise 25%).

With these settings, the photo is looks pretty clean - the chroma noise has disappeared, and there is just a little of luminance noice (the grain-like texture that you see into background). The colors looks slightly less saturate than in previous crop, due to the color noise reduction, but the difference is very slight and the detail is still excellent.

It would be possible to print this photo with excellent results, the noise would be barely visible even in large prints. That said, if you want a 100% noise-free file, it is possible to enhance even more the photo, with a selective noise reduction on background.

The first step is to dublicate the background layer (Layer>Duplicate Layer), to create a copy of the image. Now, you have the original image, in the first layer, that remains untouched, while you can apply a strong noise reduction on the copy.

To remove completely the noise, apply the Reduce Noise filter with very aggressive settings (Strenght 10, Preserve Detail 15%, Reduce Color Noise 0%).

Note that usually the color noise has been already eliminated with the first swipe of noise reduction, and now you are removing only the luminance noise. Set Reduce Color Noise on values higher than 0 only if there is still some color noise - you must not abuse of this control, even though it does not softens the detail: it reduces the color accuracy and it gives flatter, less punchy color.

If necessary, you can apply the filter twice (even though usually one time is enough), while I recommend to avoid Gaussian Blur or Median: they are very effective, but often they create a very artificial-looking bokeh. The photo becomes very clean, noise-free, but of course the detail is completely smudged: to get a good result, you have to apply such strong noise reduction only on the out of focus areas, as the background.

Select the Layer Mask (Layer>Layer Mask>Hide All), and click on the Brush Tool. The Layer Mask is one of the most powerful and versatile tools of Photoshop - if you don't know well what it is and how it works, I recommend to read the article "Layers and Layer Mask".

Now, you have to "paint" on the areas where you want to apply the strong noise reduction. Usually, I select a relatively small brush (Master Diameter 50 or 60px, Hardness 70%) and I magnify the photo to 200% to follow precisely the borders of the subject. Remember than you don't have to touch the borders with the brush - otherwise they becomes a bit fuzzy. It is always better to leave few pixels between the border of the subject the the brush.

When I have finished the fine adjustments, I select a larger brush to apply the noise reduction on the rest of the background, and finally I flatten the layers with Layer>Flatten image. The fourth crop is taken from the final image: the subjecy is sharp and rich of detail, while the backound is nicely smooth and noise-free. This workflow takes a bit of time, so I recommend to use it only on your best images; if you have to edit a large number of photos you can get quite good results even with a moderate noise reduction applied on the entire image.

The Layer palette: the white areas of the layer mask are the areas where I applied the strong noise reduction.
  

 

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