Wednesday, October 23rd, 2019

Digital Noise – What Is It? What Causes It? And How Can I Get Rid Of It?

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Digital noise in photos taken with digital cameras is random pixels scattered all over the photo. It is a similar effect as “grain” in film photography and it degrades the photo quality.

Digital noise usually occurs when you take low light photos (such as night photos or indoor dark scenes) or you use very slow shutter speeds or very high sensitivity modes.

When taking pictures with a digital camera an electronic sensor (also known as a CCD) built from many tiny pixels is used to measure the light for each pixel. The result is a matrix of pixels that represent the photo.

As with any other electronic sensor the CCD is not perfect and includes some noise (also know as white noise to hint on its randomness attribute). In most lighting the light is significantly stronger than the noise. However in extreme scenes where the light is very low or when a high amplification is needed noise levels can become significant and result in pixels in the photos that include more noise data than real photo light data. Those pixels usually appear as random dots or stains on the photo (for example white dots scattered randomly on the photo).

Understanding digital noise in various scenes:

low light (night photos or dark scenes): when the scene is dark the amount of light measured by each pixel of the CCD is low. When the light intensity is very low it can become too close to the level of noise naturally found in the CCD. In such cases some pixels can appear as noise because the noise level measured for them is significantly close or higher than the actual light intensity.

slow shutter speeds: when the shutter is kept open for a long time more noise will be introduced to the photo. A slow shutter speed translates to the CCD integrating more light per pixel. The effect can be easily understood as the CCD “accumulating” light in each pixel and measuring the total light over the shutter period of time. However at the same time the CCD is also “accumulating” noise. For that reason in slow shutter speed photos some pixels will appear as noise because for these pixels the amount of noise integrated is significantly close to or higher than the actual light measured.

high sensitivity modes: high sensitivity in digital photography is implemented by mechanisms that result in amplification. The CCD amplifies the measurements it takes. However there is no way to just amplify the actual photo light that falls on the CCD pixels instead the noise and the actual light are both amplified. The result is that the CCD becomes sensitive not only to light but also to its own noise. When too much amplification is applied some pixels will appear as noise.

While it is impossible to completely prevent digital noise there are a few options that allow you to significantly decrease it. When taking photos in low light scenarios such as night photos there are two main parameters to play with: sensitivity and shutter speed. Raising sensitivity creates more internal noise in the CCD while slowing down the shutter allows for more noise to integrate on the CCD. The amount of noise generated by both parameters is different. It is recommended that you set your camera to manual mode and play with a few different sensitivity/shutter speed pairs to find out the one that generates the least noise.

Some cameras include a built-in feature called “noise reduction”. Noise reduction is implemented by sophisticated software that can identify the noise pixels and remove them. For example the software can identify the noise pixels based on their randomness and usually extreme intensity gap between them and their neighboring pixels. Removing the noise can be implemented by interpolating a replacement pixel value based on its neighboring pixels.

If you do not have a built-in noise reduction feature or it does not work properly you can use a PC based software that removes digital noise. Many photo processing software include a combination of automatic and manual digital noise removal. Some software packages can also use a few photos of the same object to “average” them and thus remove the noise (relying on the fact that digital noise is random and the noise pixels will be different in each photo taken).

To conclude digital noise should be understood by any amateur or professional photographer. However for most photographers digital noise is not a practical problem even in low light scenarios usually digital noise is minimal and can be significantly reduced by simply turning on your camera’s noise reduction feature. For professional photographers who shoot in more extreme conditions digital noise can present a real problem and can be dealt with using a combination of optimizing the camera settings and removing noise with professional software.


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Where there is no vision, the people perish.
Proverbs 29:18

The earth is the LORD’s and everything in it, the world, and all who live in it; for he founded it upon the seas and established it upon the waters.
Psalm 24:1-2

He makes springs pour water into the ravines; it flows between the mountains. They give water to all the beasts of the field; the wild donkeys quench their thirst. The birds of the air nest by the waters; they sing among the branches. He waters the mountains from his upper chambers; the earth is satisfied by the fruit of his work.
Psalm 104:10-13

Look at the birds of the air; they do not sow or reap or store away in barns, and yet your heavenly Father feeds them. Are you not much more valuable than they?
Matthew 6:26

How many are your works, O LORD! In wisdom you made them all; the earth is full of your creatures. There is the sea, vast and spacious, teeming with creatures beyond number living things both large and small.
Psalm 104:24-25

Sometimes I do get to places just when God’s ready to have somebody click the shutter.
Ansel Adams

When you photograph people in colour you photograph their clothes. But when you photograph people in B&W, you photograph their souls!
Ted Grant

While there is perhaps a province in which the photograph can tell us nothing more than what we see with our own eyes, there is another in which it proves to us how little our eyes permit us to see.
Dorothea Lange

When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence.
Ansel Adams

Your first 10,000 photographs are your worst.
Henri Cartier-Bresson

You don’t take a photograph, you make it.
Ansel Adams

Beauty can be seen in all things, seeing and composing the beauty is what separates the snapshot from the photograph.
Matt Hardy

Nothing happens when you sit at home. I always make it a point to carry a camera with me at all times…I just shoot at what interests me at that moment.
Elliott Erwitt

Which of my photographs is my favorite? The one I’m going to take tomorrow.
Imogen Cunningham

You’ve got to push yourself harder. You’ve got to start looking for pictures nobody else could take. You’ve got to take the tools you have and probe deeper.
William Albert Allard

If I saw something in my viewfinder that looked familiar to me, I would do something to shake it up.
Garry Winogrand

I always thought good photos were like good jokes. If you have to explain it, it just isn’t that good.
Anonymous

Twelve significant photographs in any one year is a good crop.
Ansel Adams

It can be a trap of the photographer to think that his or her best pictures were the ones that were hardest to get.
Timothy Allen

 


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