Reduce Noise With Multiple Shots

Magazine - Digital Photo Pro, Software - Photoshop  Comment
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Got noise in one exposure? Make a bunch of exposures and watch the noise disappear.
You can reduce noise in an image by combining multiple exposures of the same composition in Photoshop. Photoshop can search for the differences between the separate exposures and then blend them, keeping what stays the same and eliminating what changes. Random noise between separate exposures of the same composition will be substantially, even dramatically, reduced or disappear altogether. (This technique won’t eliminate fixed noise, hot pixels, or column and row noise. There are other techniques for that, like using dark slides.)
You’ll find having this option will greatly reduce any reluctance you have toward using high ISOs. This means two things. You’ll be able to make images in lighting situations you thought you couldn’t, and you’ll be able to make handheld exposures in conditions you ordinarily wouldn’t be able to without severely compromising quality.
So how do you do this? Use the following steps.
1. Shoot multiple exposures.
Try to minimize camera motion as much as possible. It’s not necessary to use a tripod, but it’s helpful2
2. In Photoshop, go to File > Scripts > Load Files into Stack.
3. Click Browse and select the exposures to be used in the Stack and check Attempt to Automatically Align Source Images and Create Smart Object after Loading Layers.
This will create a single Smart Object from the multiple exposures. Double-clicking on this Smart Object will allow you to see the layers separately.
4. Go to Layer > Smart Objects > Image Stack Mode > Median to blend the separate exposures.
You’ll see that the noise is re-duced substantially.
5. Optionally, compare Image Stack Mode > Mean.
This works best for exposures containing no movement.
Read more about this technique at Digital Photo Pro.
Learn more about noise here.
Learn more in my digital printing workshops.

Noise – Reduce It At Capture

Magazine, Magazine - Digital Photo Pro, Technique - Exposure  Comment
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noise-capture
Noise comes in three types or patterns:
1) Random noise 2) Fixed-pattern noise 3) Banding noise
Noise often has two components—brightness and color:
4) Image noise 5) Luminance noise 6) Chrominance noise
Knowing the type and kind of noise produced will help guide you to solutions to reduce it. There are three types of noise: random noise, fixed-pattern noise and banding noise.


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Dave McDonell on Noise

Interviewed, Technique - Exposure  Comment
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noise1
Dave McDonell, cofounder of Imagenomic, the company that makes Noiseware, my favorite noise reduction software weighs in on noise.
JPC    Where does noise come from?
DM    There are several factors in a digital camera capture process that contribute to noise. The most prevelant are temperature, the actual capture circuitry, sensor size, and the process of sub-sampling which induces errors between adjacent pixels.
JPC    Why is chrominance noise so much easier to reduce than luminance noise?
DM    It’s really not in application. It’s just that you perceive changes in luminosity or brightness much easier than you do in color.
JPC    Fine color noise is easier to reduce than coarse color noise, like the color patterns created by demosaicing bayer patterns. When are you most likely to encounter this type of noise? How should you treat it differently? How far can you go?
DM    There are no hard and fast rules for any of the above questions as all are dependent on the capture situation and subsequent output medium.


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Layering Noise

Magazine, Software - Photoshop  Comment
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Here’s an excerpt from my column in the current issue of Digital Photo Pro.
“When adding noise to digital files, keep noise separate from the image so you can control both independently of one another. This way you’ve got extraordinary control and flexibility. When noise is placed on its own layer you can eliminate or change it at any time in the future, reduce its opacity, localize it, desaturate it, target it into specific channels, move it, scale it, blur it and much more …”
Read more in the current issue of Digital Photo Pro.
Learn out more in my digital printing workshops.