Managing Noise

One of the things that has been somewhat challenging with digital photography is noise. Sure, we had grain with film... and while we might have fond memories or even an affection for the look of the grain in high speed films, digital just doesn't have the same aesthetic qualities or appeal.

I don't know... maybe it's like the ticks and pops you got when you listened to a vinyl record... you could live with it. But a let a CD go bad and it's like a visit to the "bad acid tent" at Woodstock. (did I just date myself?) Seriously... even digital television is similar. In the old days, you just got "bad reception." Nowadays, you get freaked out pixelation flashing across your screen and screeching broken-up noise out of your speakers. It just seems that digital, regardless of the format, is either really good, or really bad. Analog gave us a little more room for error.

So... noise at high ISO... what causes it and how can we manage it?

Profile test patternWhile it's fair to compare noise to film grain, it's really more like color artifacts or ugly speckles in your image. Muddy and dirty looking globs tend to collect in the shadow areas. It comes from signal amplification and temperature induced current... basically causing sampling errors in the pixels.

Most cameras start having issues at 400 ISO and higher. Small point and shoot type cameras take it pretty hard... especially with the amount of megapixel manufacturer's seem insistent on cramming onto these small sensors. But even the better DSLRs have issues too.

And it's not just cameras... scanners have been doing this for years too. It just comes with the digital territory.

The folks at Picture Code who produce the software Noise Ninja, explain it this way:

Creating a camera profile.Noise is an inherent property of digital imaging sensors. The laws of physics make it impossible to completely eliminate noise, and they force a tradeoff between noise levels and other properties like sensor size or sensitivity. Photons, for instance, arrive at random intervals, so the simple task of counting them during an exposure-- which is the basic function of a pixel in a sensor -- is subject to sampling error. When the exposure is shortened or the pixel size is reduced, there are fewer photons to "average out" the sampling error, so the noise increases relative to the signal.

Sliders in default positions are relative to the scanned image profile.The small sensors in compact digital cameras are more prone to noise than the large sensors used for digital SLRs. Compact digicams often have as many pixels as their DSLR brethren, but those pixels are packed into one quarter the space -- or even less. So, for any given exposure, many fewer photons reach each pixel in the smaller sensor than in the larger one, and this leads to correspondingly higher noise. So, the noise in a compact camera at ISO 200 might be the same as the noise in a DSLR at ISO 800. By the same reasoning, an 8-megapixel camera might have much higher noise levels than a 4-megapixel camera if both have the same sensor size.

This effects photographers in several ways. When we don't have enough light, we're forced to make trade-offs. Do we shoot slow and risk soft or blurred details in our shot... or do we crank up the ISO and deal with noise? If we're looking to do large prints, both options can be disastrous. We need to keep the noise signal low so as not to have it magnify and spoil the finished look. And we need to keep the detail and edges good and sharp.

While this might not be a problem in a 4x6 snapshot, this isn't a problem. But blow up a nice 20x30 wall mount and it can be a deal breaker.

Save your profile for each camera ISO and quality setting.To give credit where credit is due, some of the new DSLRs are making amazing strides in noise reduction. But, you need to be careful in using it. And, keep in mind, some of this is simply a noise reduction process built into the software imaging engine of the camera as it produces a JPEG. So... you're giving up some control there.

I've seen decent improvements in my Canon XXD series cameras. But I'm hearing the new 50D (even though it will go to higher ISO) is not as good as the 40D at 1600 ISO. The high end Nikon seems to be the benchmark to date.

If you really want to get the best of the situation, there are a few things you can do that will help you stay in control. And the place to start (as with anything we do) is in the camera and when you take the shot.

Applying your camera profile to an image in Noise NinjaIf you're in a situation where you have to push the ISO, don't pussy-foot around. Don't try to creep up on it by underexposing a bit so you don't have to go so high on the ISO. An underexposed image is just going to generate more noise and become visible when you try to bring up the exposure in post processing. In fact, the best thing you can probably do is bump the ISO, set to the correct exposure and give and over expose slightly by +1/3 or so. You'll have a better image to start with once you begin your post process work.

Before Noise NinjaAfter Noise NinjaThere are many noise reduction programs out there. Personally, my choice is Noise Ninja. It does something that appeals to my logic... and it allows me choices without offering so much adjustment that I just get lost in it. I think it does a great job.

Now, "great job" is relative. We're still making trade-offs. After all, we shot the image in a trade-off situation... so fair is fair... don't expect miracles. But do expect images that are far superior to what you started with and tools that help you get the job done.

After Noise NinjaBefore Noise NinjaOne of the keys to Noise Ninja is building camera profiles. Now I know that sounds like something that might be out of reach to your limited software skills. Trust me, it's not. And... the benefits are huge. It only takes a few minutes of your time... and when complete, you're going to feel like a noise reduction guru.

I use the Noise Ninja plug-in for Aperture. But whether you use the Photoshop plug-in or the stand alone version, the process is the same.

Noise Ninja provides a test pattern that you download and open up to display on your monitor. Take your camera, fill the frame with the test pattern on your monitor... make sure it's slightly out of focus, and take a picture.

Now, repeat this step for every ISO setting on your camera and I would suggest you do it both in RAW and high quality JPEG. Do them all.

Before Noise NinjaAfter Noise NinjaNext, download the images to your computer and open each one in Noise Ninja. When you do this, Noise Ninja will automatically scan the image. As it completes its scan of the image it will create a profile and put each of the control sliders at a default setting. Now.. this is important... those slider settings represent the mid-range setting for THAT PROFILE. They are relative ONLY to that profile. You can adjust them to more or less... but either way, it is just a range for that particular profile. I suggest leaving them in the Noise Ninja default.

There is a button that says "Create Profile." By clicking on this, you are saving the profile for that particular test image. It will default to a name like Canon 40D ISO 400 RAW - it derived that name from the EXIF data of that image. Keep it that way. It will be important later.

So... just as you repeated the steps taking your test pattern shots, repeat the process of opening them in Noise Ninja, running the auto profile scan and saving as the default name. Do this for each test image until you've scanned and created a profile for all your settings.

Before Noise NinjaAfter Noise NinjaNow, going forward, when you bring an image from that camera into Noise Ninja it will AUTOMATICALLY apply the proper profile. How? It reads the camera's EXIF and grabs the profile you saved that contains the same EXIF data. Nice? Now you've got the default adjustments and a perfect starting (or finishing) point for Noise Ninja. You can bump the sliders up or down to adjust your image to taste. Piece of cake and GREAT results.

I've been using Noise Ninja with my Leica Digilux 2s. As beautiful as the files from this camera are... it's in agony at 400ISO. Honestly, the JPEGs probably aren't usable. It's four year-old technology. But, shooting in RAW, I can get good images from the camera and finish them off with Noise Ninja. With my Canon gear, I can shoot at will at ISO 1600, knowing with Noise Ninja I can finish them off.

Technology will get better, I'm sure. But in the meantime, it's nice to have good software to help get the job done.