Digital Darkroom; Photoshop Noise Reduction

The Digital Darkroom is a series of posts aimed at beginners and those interested in Digital Photography and Editing. In previous weeks we have looked at basic adjustments, curves, editing colour with the HSL/Color panels, black and white toning, split toning, local adjustments, sharpening, noise reduction and Lens Correction and Camera Calibration in Lightroom and Adobe Camera Raw. Moving into Photoshop we have looked at the program’s layout,basic adjustments to light, basic adjustments to colour, basic black and white adjustments, Basic Sharpening and this week Noise reduction with the Noise reduction filter, using surface blur on channels and stacking images to reduce noise.
If you wish to check out previous posts in the series you can do here.

Camera Noise is a by-product of using a digital camera and all images will have digital noise to some degree; some noise is less noticeable in some images than others due to a combination of factors.
Noise is more prevalent in images shot with; a high ISO, a small sensor size, a long lens and even longer exposures. Noise tends to stand out more in the shadows than in the highlights and will be more obvious in images that have been heavily edited especially if the shot was under exposed to begin with.
When we talk about removing noise we should not think about nuking noise out of an image, more reducing it to a level that is acceptable.

The first steps of noise reduction can be done when taking the picture; making sure the best ISO is set; do you really need to be shooting at 1/2000 of a second with the 50mm lens maybe turn down the ISO to get a short shutter speed and less noise. Also getting the best exposure that you can will help to remove noise, even when shooting raw; check the histogram on the back of the camera and preview the image, zooming in when doing so.

Too Much Noise Reduction

Noise Reduction Just Right

In the image on the right, the noise reduction has been too aggressive. The tones feel smooth and look ok. Compared the second image though you can see a lot of detail has been lost from the graffiti as well as the womans hair. Taking into consideration that the second image is darker and contrasted the noise in the image helps emphasise the detail. 

As I mentioned in the Lightroom Noise Reduction post a few weeks ago there are different types of noise. The main noise we are looking at reducing is Colour Noise as well Luminance noise, as these are the most common.
In Photoshop noise reduction is one of my first steps after an image has been opened, unless I have edited the shot first in Lightroom or Adobe Camera Raw. I do this even before sharpening as I don’t want to sharpen noise. Sometimes an image will look fine with no to little obvious noise, zoom in at 100% and you can see the grainy effect of noise.

A visual comparison of noise. Print size on the left and 100% zoom on the right.

Reduce Noise Filter (Basic)

Reduce Noise is Photoshop’s singular noise reduction tool and it can do an ok job (not brilliant but ok) in reducing noise.
In basic mode you can adjust the strength of the filter. This filter will reduce both colour and luminance noise.

You use the strength slider to adjust how much luminance noise is reduced and the preserve detail slider will help preserve edges. The luminance noise reduction will be stronger if you set the preserve detail slider to 0; using the preserve details slider you can inadvertently add artefacts to an image but also setting a 0 value will also make the image seem softer.
The colour noise slider allows you to reduce colour noise separately.

When reducing noise using this filter, I would suggest reducing colour noise first and then seeing how much luminance noise is left. This is because colour noise can be easily mistaken as luminance noise.
Once all the noise has been removed the image can seem soft. You can sharpen it a bit with the sharpen details slider. I would advise caution when using this slider because too much sharpening can add more artefacts into the image.

Advanced Mode allows you to target noise more accurately by adjusting the noise in each colour channel separately.  When doing so, if the blue channel contains more noise you may over do the adjustment on the other two channels. In adjusting each channel individually you can protect details in each channel while removing noise more aggressively in another channel.
Normally the red and green channel contains less noise than the blue channel. I would adjust the blue channel first and then tackle the others. The Strength and Preserve detail sliders work the same as in Basic mode.

The amount of noise reduced does not seem so much but there is evidence of a generally smoothing of the noise. Viewing the image at print size not shows a much more printable image.

 

Reduce Noise Comparison Before and After. Before on the Left after on the right.

 

Surface Blur On Channels (A Bit More Than Basic)

Taking a hint from the noise reduction filter and using the advanced setting to reduce noise on a channel by channel basis, you can do something similar with surface blur and Channels.
In CS5 you could apply surface blur to the channels with the image layer as a smart object. In CS6 and CC if your layer is a smart object, you will need to duplicate the layer and rasterize it or create a new layer and use the shortcut Shift+Ctrl+Alt+E. Then apply the filters to the channels with this new layer active.

To start you need to click on the channels pallet, which is next to layers where your image is. When you do this and the image is in RGB colour mode you will have 4 channels; the combined information channel – RGB, then one for each colour, Red, Green and Blue. You can edit each channel individually and this is the next step.

Zoom in at 100% and view the channels. Select the first channel and go Filter-Blur-Surface Blur. Surface Blur is a blur filter that blurs an image while preserving edges.
The filter has two options Radius and Threshold. Radius controls the size of the blur.
Threshold in this case helps to control what will not be blurred. The setting of threshold is in levels; the lower the setting the effect of the blur is less preserving more edges, moving the threshold higher preserves only the larger edges.

This has worked really well in remove noise from the shadow areas that was quite strong, and as I would expect there is still some noise but once again at print size it is not distracting. The method has softened the image more than using the Reduce noise filter.

Before and after of surface blur filter applied to channels. Before on the top after on the bottom.

 

Reduce Noise With Multiple Exposures (A Bit More Advanced)

For moving subjects or scenes where there is a lot of movement this next method will not be too helpful. But if you have a stationary scene with little movement a bit of forethought, then this method may save your bacon.

 

Either in Adobe Camera Raw or Lightroom select the series of images taken, right click and open them as layers in Photoshop.
Select all layers and align the layers (edit auto align layers).
Set the back ground layer’s opacity to 100% and set the next layer’s opacity to 50%; half the opacity for each layer after eg Layer 1-100 Layer 2-50 Layer 3-25 Layer 4-13. When I get to An opacity of 1 each image after I set the opacity to 1.
The more images you have the more noise will be reduced. The reason this works is because noise is random and in each image the noise will be in a different place. Reducing the opacity works by letting only part of the information of that image through smoothing noise but leaving repetitive detailed areas sharp.

On the right is the noise from the original photo and on the left the reduced noise from stacking exposures.

 

 

This process can be done by automatically by Photoshop itself an produces a much cleaner image.

Just as in the previous process you need to open a group of images as layers and have them aligned.
Select all layers, right click and convert to a smart object.
Remove noise via Layers-Smart Object- Stack Mode- Median.

On the left the manual stacking process and the on the right median stack mode.

 

What Method Should I Use?

Which method you use is up to you. If you are new I would try just to use the Reduce Noise filter and practice in advance mode and see what results you get. I do find that with medium ISO images this filter works really well.
Surface blur on channels I find works well on images with a lot of shadow noise but you need to be careful that you don’t blur details to much. This may take some experimentation.
The stacking method is something I will use often with high ISO or pictures taken on my phone, as I said this needs forethought but if the scene looks incredible, shoot in burst mode.

There are many third party plugins and filters you can buy that are better than Photoshop’s noise reduction methods for single images. Topaz Labs and Nik Soft both have very powerful noise reduction filters that work great with high ISO images. Personally if you are looking for something to seriously tackle noise, I would invest in a third party plugin.

Emo Girl

Fish in Aquarium

Noise Reduction Just Right

 

If you have any questions or comments please use the comment box below, all are welcome as this series is designed to help people learn how to use Photoshop and Lightroom.

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