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Noise Reduction for Digital Photos

One of the great advantages of digital over film photography is the ability to select your ISO on the fly. By increasing the ISO, you are able to retain reasonable shutter speeds even in low light environments. Cameras such as the Canon 10d provide ISO equivalents as high as ISO 3200. As the sensor's gain is increased to provide higher sensitivity, digital noise becomes more apparent. While the Canon 10d has little noise below ISO 800, it becomes progressively more apparent with higher settings. The newer Canon 20d has much better noise reduction built-in, reducing the work to be done in post-processing on the computer.

Even with onboard noise reduction, there will always be a need for post-processed noise reduction. In fact, it is better (although more time-consuming) to reduce noise on a computer because reduction settings can be tuned to the particular image content, rather than trying to apply the same settings across all images. Fine details (eg. natural noise-like features, such as sand, asphalt, etc.) might be mistakenly removed by an automated reduction algorithm.

There are a number of products available to reduce noise, and a quick summary is shown below.

The two most notable stand-alone solutions to noise reduction are: NeatImage and Noise Ninja. Even in the absence of a stand-alone noise-reduction tool, Photoshop itself provides some decent means of noise reduction as well.


Neat Image Pro+

Offering very extensive fine-grained control over the noise-reduction process, NeatImage is certainly amongst the top tools in terms of features and performance. One is also able to create a set of profiles for your particular digital camera, that can be the basis for future noise reduction work.

Trying to decide between NeatImage and NoiseNinja was difficult, as they both are well-respected tools. However, NeatImage is the only one (as of November 2004) that offers a Photoshop Plugin. This requires a purchase of their "Pro+" version, the most expensive choice, but I feel it is well worth the money. NoiseNinja had been beta-testing a Photoshop plugin over the last few months, and I believe it is now available in a released form (December 2004).

The advantages of having NeatImage integrated directly into your Photoshop workflow (as a plugin) are plentiful. In particular, one often wants to adjust noise reduction variables on a picture-by-picture basis. Noise reduction is a process that is not well suited to complete automation.

The computer has no idea what you have taken a photo of, so it cannot determine what truly is noise and what is simply texture. With our innate ability to perform advanced image recognition, we can easily recognize a pattern as being asphalt or speckled sand, whereas the computer might simply assume it to be noise. If the computer were allowed to remove these natural "noise-like" regions from photos, many textures would be destroyed, leaving a "plastic" look in its place. Therefore, it is important that the user is still involved to some degree in the reduction process.

Therefore, it is generally less desireable to apply the same degree of noise-reduction to all images, which makes a standalone batch tool less useful.

More importantly, however, is the fact that a tight integration within Photoshop allows for localized noise reduction, practically impossible with a standalone tool. Once can simply create a duplicate layer that contains the results of the noise reduction, and then apply a layer mask with opacity to blend varying degrees of reduction across the image.

It should be noted that noise reduction is a compute-intensive task, and the speed of your processor will be the deciding factor in how long you'll need to wait for the reduction tool to complete a single photo. For my test example, I am running NeatImage Pro+ on a 6 megapixel photo, shot at ISO 800 on a Canon 10d digital SLR camera (the actual file size is 2.67MB). In my tests, the initial noise "auto profile" analysis takes 8 seconds, the actual noise reduction process when applied across the entire photo takes 31 seconds. This is on a 2.5GHz AMD Athlon XP processor with 768 MB RAM. Obviously, if you are running an older or slower machine, you can expect moderate wait times.

The better noise reduction tools provide many adjustments that allow the removal of digital noise or scanner noise without losing much detail or sharpness. The example below demonstrates the "out-of-the-box" quality that is achieved with NeatImage without any tuning whatsoever (or sharpening). It should be realized that better results can be achieved with minor adjustments to the profile.

Before Noise Reduction ( 100% Crop from Canon 10d, ISO800 )

After Noise Reduction ( 100% Crop from Canon 10d, ISO800 )

Noise Removed by NeatImage ( Enhanced difference between before & after )

Workflow with the NeatImage Pro Photoshop Plugin

The first step in using the plugin is to select a layer in Photoshop and then invoke the plugin from Photoshop's Filter > Neat Image > Reduce Noise... option..

Neat Image 4.32
  Home Home+ Pro Pro+
Cost: U$29.90 U$49.90 U$59.90 U$74.90
Features: 8bit, 10 batch. 8bit, 10 batch, Plugin. 16bit, Unlm batch. 16bit, Unlm batch, Plugin.
Vendor: AB Soft
Web: www.neatimage.com
Prices as of November 2004

Photoshop CS

Photoshop CS doesn't really provide any decent built-in functionality, but a number of photoshop actions exist that perform some degree of reduction. Most notable are the actions offered by Fred Miranda. He has a series of actions that target various needs of digital photographers: noise reduction, sharpening, resizing, etc. Most of these are far better than the built-in methods provided directly from within Photoshop. It should be noted, however, that these are essentially scripts that perform numerous steps that a person could do within Photoshop, but with far more ease.

 


Reader's Comments:

Please leave your comments or suggestions below!
2008-08-13DDT
 MartianBachelor's point of view is a good example of how our left hemisphere can be so wrong.

FOR HUMANS

If noise reduction makes you think that noise is gone, then noise IS gone because your perception is more important than theory.. at least for arts.

FOR MATHEMATICIANS

For you math lovers, I state that noise reduction can actually improve the signal to noise ratio. Just shoot a plain white sheet of paper, then apply noise reduction. Whoo hoo ! The signal to noise has been improved (where the signal is the original light that entered the lens). Noise has NOT been "moved around", it's actually GONE.
In order to do that, the plugin "contains" information about the image which the sensor did not capture... what is this information is left as an exercise for the reader ! It is very simple.

Close your math books and use your own neurons once in a while, I tried it and it's fun ;)

P.S. Great site, keep on the good work.
2008-05-22ahsan khan
 its wonderful i already use it on professional level
2007-02-13Tim Macking
 I use Noise Ninja, it's an awesome product. Worth the price $$$. Tim Macking - MCSE
 I think one can't go wrong with either NN or NI -- both are excellent.
2005-12-21Vitaly
 new algorithm jpeg noise reduction

My name is Vitaly Bursuk. I am from Russia.

I suggest your experts to familiarize with results of work of new algorithm which deletes jpeg artefacts of the image. I think it it will be interesting. Results of work are located at Dejpeg .

I Shall is glad if you will state wishes or remarks in this occasion.
If there are questions and the comment shall be glad to you to answer.

Best regards Vitaly.
 
2005-10-11MartianBachelor
 

I think it's somewhat misleading to go along with the manufacturer's claims that code such as Neat Image performs "noise reduction". It doesn't. I really just moves the noise around. Claiming one has reduced true (random) noise is something like claiming one has invented a perpetual motion machine.

Anything one does to a digital image can only *reduce* the signal-to-noise ratio, not improve it. This is especially true where only 8 bits per channel (i.e., 24-bit color) are being saved out because then one is adding quantization noise to the image.

Does this mean the image doesn't *look* better after applying Neat Image? No. But it's not because the noise has been reduced any.

 

Absolutely! Yes, refering to it as noise reduction might very well be a bit of a misnomer, but it will be forever be engraved in laymans' minds that this is what it is doing. Most people do, however, recognize that one does lose detail in the process. You can't increase the signal to noise as you point out. But in limited quantities, tools such as NeatImage or Noise Ninja do a great job at reducing the appearance of visible artifacts of color noise that plague high-ISO digital images. This is also very useful in reducing image file size of these images while still retaining decent aesthetic quality. Any noise tool taken too far will leave an unnatural plasticky appearance.

2005-03-16Anonymous
 

can you do a comparison with noise ninja from picturecode.com? i've also heard that this was pretty good software.

 

Yes... I plan to add a comparison between these two, especially now that NoiseNinja has a Photoshop Plugin available

 


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