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Noise Reduction Guide for Digital Photos

Photo & Video

Even though the image quality of digital cameras keep getting better and better with every generation, there’s still room for improvement in the high ISO noise department. As long as the cameras allowme to take photos that’ll show noise, I’ll do it if it means thatI can use natural lighting and sufficiently freeze the subjects movements. The highest selectable ISO setting will usually result in photos that are close to unusable, the next highest in photos that are usable but containing clearly visible noise and two stops down from the max ISO the camera takes photos which are essentially free from noise.This guide will show how to make the noisiest photos usable and make the ones on the border worthy of large prints.

Luma vs. Chroma Noise

The most visible noise in a photo is the blotches of chroma (color) noise. Luminosity noise is usually seen as less ugly and visible. By using a weaker luma noise reduction and stronger chroma setting the detail from the luminosity information is preserved while visible noise is reduced.

Shadow Noise

Noise is most visible in dark areas where any lighter spots (especially colored) will stand out against the background. There’s a clear trade-off between shadow noise and detail retention, the details in dark areas are often barely visible and applying strong noise reduction often kills them. The choice is to keep the details and the noise or getting rid of the noise along with the details. If detail loss is acceptable in the darker areas an additional stronger noise reduction layer can be created which is masked in, it can also be applied to only some of the dark areas.

Workflow

I use Adobe Lightroom to import, develop and export my photos. I import as DNG since I believe that it’s a format that’ll live a little longer than the propriety manufacturer RAW-formats. Since I started using Lightroom my postprocess work has speeded up immensely compared to using Canon DPP or Photoshop and then some other kind of browser (like Picasa). Exporting to a new resolution for print or web is a matter of a few seconds instead of a couple of minutes of browsing, opening, rezising and saving somewhere. Apples Aperture works in a similar way but I’m not using a Mac so it’s not choice for me.

As a result I need a software solution which is compatible with Lightroom. The built in noise reduction works well with moderate amounts of noise (think clean up and not rescue) and it allows me to open a 16-bit copy of the photo in Photoshop by pressing Ctrl-E in the Develop module. Inside Photoshop I can apply filters, work with layers and anything else I want to do and once I’m ready the new image shows up in Lightroom ready for exports.

Comparison Between Noise Reduction Software

There are two major standalone software packages to reduce noise; Noise Ninja from Picturecode and Neat Image. All major RAW-converters also feature noise reduction algorithms (and settings) as well as Adobe Camera Raw found in Lightroom and Photoshop. Just like the cameras can allow excessive noise amounts, these software packages also allow excessive noise reduction will will destroy details and smear colours which makes the photos look very artificial and really not acceptable. In this comparison I’ve reduced noise until smearing and detail loss becomes unacceptable, although this approach isn’t very scientific I can’t think of any other method since there are to many unknown parameters and algorithms in the software.

Canon DPP

Many say that themanufacturers own RAW-converters are the best ones to use since they have all the intricate knowledge of the sensor, camera and file format. The examples used here are from a Canon EOS 40D which means that the natural processor is the Canons Digital Photo Professional. The fact that the program is somewhat unintuitive to workin and tough to use in any managed workflow makes it a no-go, but it’s good as a reference.

Adobe Lightroom

Lightroom is capable of cleaning up this ISO1250 and 1600 photo nicely, by setting Luma and Chroma noise reduction to 25/75 detail is preserved while most of the noise is removed. Once stronger noise is found it has a harder time. The big benefit is that it’s available along every the other develop setting in my main postprocessing package.



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