5 Great Ways To Eliminate Image Noise At The Source

Reflection XXXVII

high noise / low noise

Noise happens. There is always some degree of noise present in any electronic device that receives or transmits a signal. Though noise is unavoidable, it can become so small relative to the signal that it is no longer visible. It’s all about a good signal to noise ration (SNR). The image is the signal. The capture and carrier mediums’ biproducts are the noise. (Film grain is noise.)The higher the SNR the more the image overpowers the noise; the lower the SNR the more the image becomes confused with noise. While some noise increases the apparent sharpness of images, the vast majority of noise found in images degrades quality. It’s best to avoid it.

There are a number of things you can do to reduce noise in your digital images at the point of capture.

1       Expose to the right
2       Use lower ISO settings
3       Use bigger sensors
4       Use faster exposure times
5       Keep equipment cool

Start here. Use software to reduce the appearance of noise only when needed. (Of course, reducing noise may not be the only deciding factor when selecting conditions, tools, and techniques. As with all things, you will have to balance many concerns simultaneously. Adhere to the above principles when practical.)

Knowing how noise is produced will help you avoid it.

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avoid the red zone, caution in the yellow zone, go for the green zone

ETTR
Underexposure results in more visible noise. Darker regions contain more noise than lighter regions in digital capture; the opposite is true of film. This is because the darker regions are recorded with fewer photons and less bits of data. It stands to reason that darker regions of images are produced with fewer photons. But why are they recorded with less bits of data? Digital cameras record data in a linear progression. If a digital sensor is capable of recording 14 bits of data (or 16,384 shades of gray) with a dynamic range of 8 stops, the lightest stop contains half the data in the file; the next lightest stop contains half as much data; and so on; it generates this progression from dark to light – 32 / 64 / 128 / 512 / 1024 / 2048 / 4096 / 8,192. This means you want to expose to the right. Avoid the lower 2 stops whenever possible; they contain less than 1% of the total data in the file. With so little data the signal becomes confused with the noise; the signal to noise ratio is very low. What’s more, when these tonal regions are adjusted, brighter or contrastier, the noise contained there quickly becomes more pronounced and with so few bits of data it also has a tendency to posterize. In addition, significant under exposure greatly increases the chances of producing Bayer pattern noise, a type of noise that is seen in larger areas and is more challenging to remove in post-processing. You’re much better off making a light exposure and darkening the Raw file during post-processing; this way your shadows will be represented with much more data and contain less noise. When light becomes challenging, which should you choose – under expose (without clipping) or raise the ISO? The precise cut off point is different for every camera, but in general avoid the lower 20% of the histogram. You’ll get less noise if you boost ISO and move the histogram up.

ISO
Higher ISOs amplify noise. ISO (International Standards Organization) is a descriptor that signifies absolute sensitivity to light. A digital sensor has one native ISO. Higher ISO settings simply boost the resulting signal. This is useful, but not ideal. When the brightness of the image is boosted, the noise is too.

Use “Shorter” Exposure Times
Longer exposures generate more noise. Hot pixels become hotter. All sensors have a few pixels that heat up faster than others, producing brighter than expected values. Some even have a few dead pixels that never fire, producing only black pixels. During longer exposures hot pixels are given more opportunity to heat up, growing brighter still; slightly hot pixels not visible at shorter exposure times become visible. As digital sensors age, hot pixels may become hotter and more pixels may become hot. Hot pixels produce a consistent fixed pattern of noise that can be recorded for given exposure times, making it easy to reduce. There is a duration at which a sensor suddenly produces a lot more noise; in older models this could be seen in exposures lasting only one minute, but with newer sensors this is greatly extended and most users will not encounter this; if you’re making very long exposures it’s useful test this and find the duration at which this happens for a your specific camera.

Use Bigger Sensor Sites
When it comes to noise, bigger is better – theoretically. Bigger sensors have more light gathering capacity, producing a higher signal to noise ratio, or cleaner images. More isn’t necessarily better. Cameras with more photosites (yielding more megapixels) packed into smaller areas tend to produce a lower signal to noise ratio, or noisier images. That said, a stronger signal does not necessarily guarantee lower noise. It’s the relative amounts of signal to noise that determines how noisy an image appears. The way a camera processes the file it makes has a significant impact on the final quality. Consequently, many medium format cameras that produce beautiful files in daylight typically produce noisier files than DSLR’s with smaller sensors in low light.

Stay Cool
High temperatures exacerbate noise. Thermal energy (leakage current) in semiconductors can generate an electrical signal that is difficult to distinguish from the optical signal. Ambient temperature increases leakage current by a factor of 2 for every 8 degrees Centigrade. Whether due to ambient temperature (You might start to see some effect over 90 F / 32 C degrees.) or storage (Don’t leave your camera in the sun, especially on a car seat, for long periods of time.), your camera can get hot and this will increase noise, which you can reduce by cooling off and keeping your camera cooler.

The best way to avoid noise is to produce as little of it as possible during exposure. These five tips will help you do just that.

Noise Reduction With Noiseware – The Best Photoshop Plug-In

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Before & After Noiseware

Who doesn’t have noise? If you don’t run into noise in your digital images, at least once in a while, you may not be pushing the envelope enough. You can photograph long after dark; if you haven’t tried it, you owe it to yourself to experience this—it’s magical. And if you find you don’t have a DSLR on hand, this should be no reason not to make pictures with a point-and-shoot or cell phone.

Whether you’re using a cell phone, a point-and-shoot digital camera or a DSLR at high ISOs or with very long exposures, you’re bound to run into some noise. Noise happens. When you have it, there’s a lot you can do about it. There are many ways you can reduce noise during postprocessing; you could even say there’s an art to it. Learning these techniques can improve good exposures and save others.

If Lightroom and Photoshop fail to adequately reduce noise in your images, it’s time to move to third-party plug-ins. For years, they’ve done a superior job of reducing noise, and they still do. While there are many fine third-party plug-ins for Photoshop (Noise Ninja, Neat Image, Dfine, etc.), one stands out from all the rest: Imagenomic Noiseware Professional.

For me, Noiseware is the most robust noise-reduction software available. Ironically, while it offers the most sophisticated feature set, very often the default settings when you first open an image are all you’re likely to need. In many cases, very little, if any, additional tweaking is necessary.

In part, this is because Noiseware analyzes the images you process and creates “profiles” or saved settings that it uses every time you open a new image. It intelligently learns your needs by tracking your past images and analyzing your new images. You can also use Noiseware’s tools to create your own profiles, which can be saved and reused. You can save your own Preferences for how you’d like Noiseware to behave and learn. Noiseware also offers 13 default settings (like Landscape, Night Scene, Portrait, Stronger Noise, etc.) and allows you to save your own custom settings, which can be created from scratch or by modifying the provided presets.

PresetsGeneric Standard Presets

PresetsCustom

Custom Preset

Noiseware’s ability to target noise reduction to specific aspects of an image is what makes it unparalleled. You can adjust Noise Reduction based on Luminance or Chrominance; higher settings produce stronger noise reduction. You can target Noise Level based on Luminance or Chrominance; higher settings tell the software there’s more noise. You can target Color Range; Noise Reduction and Noise Level can be customized by hue—reds, yellows, greens, cyans, blues, magentas, neutrals. You can target Tonal Range; Noise Reduction and Noise Level can be customized for shadows, midtones and highlights. You can target image areas based on Frequency (or amount of detail); Noise Reduction and Noise Level can be customized to High, Mid, Low and Very Low frequencies. Finally, you can enhance detail, first, by using Detail Protection to reduce the effect based on Luminance or Color, and second, by using Detail Enhancement, which provides Sharpening, Contrast and Edge Smoothening.

TonalColorRange

Defaults

LevelReduction

Noise Level helps prepare the filter by analyzing the image

Noise Reduction is the blurring effect

Detail_Only

Detail Enhancement – turn it off and use Photoshop instead

Frequency_Only

Frequency (of detail) targeting

TonalColorRange_Only

Tonal & Color Range targeting

Noiseware’s ability to provide this level of selectivity is extraordinary. It allows you to easily customize noise reduction for separate areas of an image without making complex masks. You’ll want to do this. Here’s just one example, among many, of why you want to do this. Smooth image areas reveal noise much more readily and they support more noise reduction, while highly textured image areas hide noise, but don’t support as much noise reduction without compromising apparent image sharpness.

Use Noiseware’s sharpening sparingly (if at all) and only for the most modest boosts to image sharpness, as you can create much more sophisticated and selective results in Photoshop—and almost every image can use a little sharpening after noise reduction. Always reduce noise before sharpening.

Combine today’s digital cameras with the latest software, and you’ll find that you’ll rethink many things about when and where you make exposures. You’ll shoot at higher ISOs that you once thought were unusable. You’ll shoot in low levels of light where you once thought it was impossible to get an exposure, much less a usable one. You’ll look at your digital files, and where once you thought noise was a deal-breaker, you’ll find it no longer is. Noise-reduction skills and noise-reduction tools are essential to any photographers skill set and toolkit. Master them, and liberate yourself.

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Reducing Noise with Adobe Camera Raw and Lightroom

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Lightroom’s Detail panel

Reducing noise in Adobe Camera Raw and Lightroom (the controls and results are identical) is easy.

The Detail panel provides tools to reduce two kinds of noise – Luminance (light and dark) and Color. Results can be targeted with the Detail slider into smoother (low setting) or more textured (high setting) areas. The effects for luminance noise reduction can be further modified by adjusting the Contrast slider; a higher setting affects only high contrast noise, while a lower setting affects even closely matched values. And finally, the effects for color noise an be further modified with the Smoothness slider, a higher setting creates a more aggressive effect.
Zoom into an image at 100% magnification and move the sliders until noise is reduced, but image quality isn’t compromised. Use restraint. In a majority of situations, it’s better to preserve a little noise than to blur the image substantially.

All noise reduction blurs images. Sharpening after noise reduction during RAW conversion is recommended. Knowing that you’ll sharpen an image after noise reduction, you may reduce noise slightly more aggressively initially.

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no noise reduction

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appropriate noise reduction

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excessive noise reduction

There are limits to how far you’ll want to go. Noise can be so aggressively reduced that surfaces within images become textureless and begin to seem synthetically rendered with software rather than optically captured photographically. This effect may become more pronounced if contours are strongly exaggerated during sharpening. While sharpening, take care not to accentuate noise further. Develop a sensitivity to texture and contour, and use your best judgment. You know what things look like. Make your images look convincing to you, and you’ll quickly convince others.

RAW converter tools have limits. RAW converter tools do a good job with moderate amounts of color noise. Even high settings don’t tend to compromise image quality; sharpness, saturation and hue variety are all preserved. But sometimes they don’t go far enough. For aggressive noise reduction, especially for larger noise produced by Bayer pattern demosaicing, turn to Photoshop and possibly third-party noise-reduction software.

RAW converter tools do a reasonable job with luminance noise, but aggressive applications may compromise sharpness (some, but not all of this can be compensated for with RAW converter sharpening tools), and at times they don’t go far enough. When you encounter situations like this, turn to Photoshop and third-party noise-reduction software.

Most images can benefit from a little noise reduction and sharpening during RAW conversion. For many situations, this is all the noise reduction you’ll need. Many exposures don’t require substantial post-processing. However, some exposures require more power and finesse than these tools can deliver. When you encounter these, move to more sophisticated tools found in Photoshop and third-party plug-ins. But always start here.

Resurrecting Detail In Challenging Images With Photoshop

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Before channel blending

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After channel blending

Big problems call for big solutions. Blending channels is a powerful color adjustment strategy that can handle even the biggest challenges.
Color adjustment occurs by modifying the tonal structure of individual grayscale channels. Typically, the information within them is adjusted. Less typically, the information within them is replaced.
Blending channels is one way of replacing them. Blending channels takes information from one channel and combines it with information from another. Rather than simply enhancing existing tonal values, blending channels reshapes one channel’s tonal structure with another’s. Consequently, in a most cases, blending channels calls for a substitution of information by percentage not a wholesale replacement of the deficient channel. You usually blend channels from different versions of the same image because blending channels from different compositions produces a highly altered effect.
Blending channels is complex. It often produces additional unintended color affects that may require further correction, such as shifts in hue that aren’t uniform across the tonal scale. Blending channels is neither the simplest nor the most direct path to color adjustment, but in certain situations (files that are exceptionally problematic) it may be the best path. The resulting benefits can be dramatic.
When is blending channels appropriate? In extreme cases. Blending channels is designed to correct major color deficiencies. It’s recommended if a channel is severely deficient, either globally or in select areas. For example, by being extremely light or dark or having very low contrast, a channel may be lacking desired detail. That detail can be found in another channel. Fine-tuning color is best left to more traditional methods of color adjustment.
Many Methods
There are several ways to blend channels; Channel Mixer, Apply Image, Calculations, and using channels as layers. Let’s review the options in detail.
1_ChannelMixer_1
The Channel Mixer (Layer: New Adjustment Layer: Channel Mixer) blends percentages of channels within a single document. It can be applied as an adjustment layer and so corrections made this way can be changed or masked indefinitely. It cannot be used to blend channels from two documents. The Channel Mixer is an excellent choice for making global (the same percentage of channels for the whole image) color to black-and-white conversions. If you want to control black-and-white conversions locally (different percentages of channels for different image areas), use channels as layers instead.
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3_Calculations
The commands Calculations (Image: Calculations) and Apply Image (Image: Apply Image) can also be used to blend channels. With these two commands you can combine any two channels, from different documents, from any layer, at any opacity, with most blend modes. With Apply Image you target the channel you wish to change. With Calculations you blend to create a new document, a new channel, or a new selection. Neither Calculations nor Apply Image can be used as adjustment layers or layers, consequently corrections you make with either of these features are made permanently to an image. With Apply Image and Calculations you can take advantage of two less frequently used blending modes not found with other tools (Add and Subtract) but you cannot take advantage of four frequently used blending modes (Hue, Saturation, Color, and Luminosity) – even if you use the Fade command.
For the greatest control and flexibility use channels as layers. How do you do this? Copy any channel and paste it into any destination as a layer. (Target a channel (click on it); copy it (Select: All; Edit: Copy); then target the master channel (RGB) and paste (Edit: Paste).) You can activate, deactivate, mask, change, or replace this new layer indefinitely. Use Layer Styles (double click on the layer icon in the Layers palette) to determine Blend Mode, Opacity, Advanced Blending (to select which channel is affected) and Blend If options (to determine how This Layer affects the Underlying Layer or which values of the overlying layer affect the values of the underlying layer). What’s more, you get a dynamic preview of any changes you make while you make them. The adjustments you make are flexible, so you can remove them or fine-tune any of the settings future editing sessions. You can even blend two or more channels first, as layers, and then use the resulting new layer to blend with the Background layer. By turning channels into layers, you can achieve everything that the other methods achieve and more.
One File, Many Channels
You may be surprised to find that every file has at least ten channels to choose from. How do you get so many? Consider the file in different color spaces – RGB, CMYK, and LAB. Convert a duplicate file into another color space and you can use any and all of the resulting channels. In fact, you can choose between many, many more channels when you consider that when converting to CMYK there are five different options for generating a Black Plate (None, Light, Medium, Heavy, and Maximum) with two styles for each with two Separation Types (UCR and GCR). But, for the vast majority of situations, I recommend you try to keep things as simple as possible and stick with the standard three.
Be cautious with older files and lower end scanners when blending with the blue channel as it often contains significant amounts of noise. In fact, in some instances, blending channels can be used to replace some or all of the blue channel and thereby remove unwanted noise. Unlike blurring or despeckling, this method of removing noise will not compromise sharpness, but it may produce unwanted color shifts that will require subsequent correction.
A Good Preview
The possibilities are staggering. Is there anything that can help with the decision making process? Yes. A good preview. You’ll want to have multiple documents of the same image in different color modes (RGB, CMYK, LAB) visible at one time to simultaneously see the blended and the blendee. You may even want to make a side-by-side comparison of the component channels of a single document. To do this, use the Split Channels option in the Channels palette submenu. This command will break a single multi-channel document into multiple single-channel documents. (If a file has layers it must be flattened first to use Split Channels.) While doing this with several documents will quickly fill a screen, having the channels separated makes evaluating their relative merits infinitely easier.
Classic Strategies
With so many possibilities, how do you choose one channel as the best candidate to blend with another and how do you use it?
First, identify the channel causing the problem. Then, find the channel with the best contrast in the areas you wish to enhance (at a low opacity) or replace (at 100% opacity). (Stronger adjustments require higher opacities.) Finally, deal with any unintended side effects.
There are several tried and true strategies for dealing with classic problems. First, create detail where there was none before. Second, create contrast that wasn’t there before. Third, add more contrast to existing tonal relationships, if the values can’t be adequately enhanced using Curves.
Look to the Luminosity channel in LAB. Look to the black plate in CMYK. Look to complementary colors. Complementary colors often contain the best possibilities for increasing contrast (Red and Cyan, Green and Magenta, Yellow and Blue), in highly saturated values.
What are you looking for? Better detail in shadows or highlights, better contrast, and a similar tonal distribution. If you change the relative distribution of tones in a channel, you’ll create a non-uniform color shift where some colors will shift more dramatically than others.
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Sometimes channel blending produces unintended side effects.

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In most cases, these side effects can be cured.

Blending channels can produce unintended side effects. There are times when it’s better to achieve the necessary effect with this technique and accept its side effects, if the side effects are easier to cure than the initial problem. Typically, all that’s required is a little dose of additional tonal enhancement, either to the master channel (tone and contrast) or a single channel (color). If you find this is not the case, take this as a sign that this is not the right technique for the problem you face.
BlendModes

Layers offer many Blend Modes 

Control The Mix With Blend Modes
As well as controlling the amount channels are blended you can control the way they are blended, by using blending modes. Blend modes determine how new values are mixed with old values. There are dozens of blend modes to choose from.
As color adjustment is achieved by altering the luminance (light and dark) values of select channels (Channels create but don’t contain color or saturation.), when it comes to blending channels, you can limit the number of blend modes you use to those that affect tone; five are particularly useful – Lighten, Screen, Darken, Multiply, and Luminosity.
Lighten displays the lightest values of both This Layer and the Underlying Layer; its neutral color is black (you can’t lighten with black).
Screen multiplies the inverse values of the pixels lightness or darkness. It’s like registering same image in the same location from two projectors. Think of it as industrial strength lightening. Its neutral color is black (you can’t lighten with black). Screen can do wonders for opening up deep shadows. It has a tendency to blow out highlights. Use a contrast mask to remove the effect from highlights.
Darken displays the darkest values of both This Layer and the Underlying Layer; its neutral color is white (you can’t darken with white).
Multiply multiplies the values of the pixels on both layers and then divides by 255. It’s like registering two identical transparencies on a light table. Think of it as industrial strength darkening. Its neutral color is white (you can’t darken with white). Multiply can do wonders for reclaiming subtle highlight detail. It has a tendency to block up shadows. Use a contrast mask to remove the effect from shadows.
Luminosity combines the luminance values of This Layer with the hue and saturation of the Underlying Layer; it has no neutral color.
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Enhance The Blend
You can enhance a channel before (or if you use channels as layers after) blending it with another. Use any adjustment method that makes the data better to blend with. As you’re blending with black-and-white images, Curves is usually all you need for it offers the most precise control of tone. For instance, you might increase the contrast of an image before using it to blend with. If you’re using the channels as layers method, all you have to do is group a Curves adjustment layer to the new layer being used to blend with. The contrast of overlying layer can then be fine-tuned as the blend with the underlying layer is occurring. This way you don’t have to guess how much contrast needs to be added before blending, instead you see how much contrast to add while the blend is occurring.
Constraining The Effect
While blending channels may solve problems that other adjustment methods can’t, they may also produce new problems.
In a great many cases, if the tonal distribution of a single channel is substantially altered using another channel, color may shift in an unintended manner. If this happens simply make an additional adjustment to eliminate any side effects. There are times when the color shifts you encounter will be non-uniform (more in some areas than others), which may lead you to making more complex corrections than you had anticipated.
If the problem solved with channel blending and the resulting side effects lie in different areas of the image, consider masking away the side effects rather than correcting them. There are several ways of masking the side effects of channel blending from selected areas. One, simply brush them away by painting with a black brush on a layer mask. Two, use a contrast mask to hold back the effect from highlights or shadows. Three, use the Blend If function in Layer Styles; by sliding the black arrow to the right or the white arrow to the left you drop out the effects from values below or above them – by holding the Option key (Command on PC) you can split the sliders to fade the effect more smoothly.
If you think you’re not used to blending channels, think again. Every time you turn a color image into a black-and-white image you blend channels. In a grayscale conversion three channels are blended to create a single channel while when using either Hue/Saturation or Channel Mixer three channels are blended to equal RGB values. But, when it comes to color adjustment, blending channels is used infrequently, perhaps because it’s so little known. Blending channels is a sophisticated adjustment method. In a majority of cases you don’t need a method that’s this complex. Blending channels is best used in exceptional situations for enhancing originals with substantial problems. If you find that you use this technique frequently, you’re probably not addressing the real problem, the quality of your originals. Nevertheless, when you run into files with severe problems, blending channels will often save the day.
Read more on Color Adjustment here.
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