Monday, June 23, 2008
The Battle Between Noise & Sharpness
Shooting at high ISOs and tweaking sharpness in an image can introduce excessive noise. Balancing these two aesthetic elements is an art.
Depending on your camera, it has some sharpening performance; the same is true for imaging software. When sharpening the image, noise will be sharpened along with the image's native details. If you object to the noise level and apply too much noise reduction, your image becomes softer. So be careful about setting your camera and software's sharpening settings. Be alert that your choice can have a dramatic effect on the appearance. Finding the “balance point” in sharpening is key.
Some advise to turn off sharpening in your camera and apply sharpening only in your computer. If you follow that advice, you'll see unsharp pictures on your camera's monitor, and an initial review in your computer will show soft images. Choose RAW files, and make an in-camera sharpness selection to get a good view on the monitor. During editing, if you choose, adjust the original camera setting with an alternative software selection. I use Nikon Capture NX software. It lets me turn off the camera's original base setting and reapply it or use Unsharp Mask or both, all while viewing each tool's effects on the monitor. If I change my mind, I can go back to the original or any other selection. Photoshop CS3's Unsharp Mask and Nik Software's Dfine version 2.0 used for selective image sharpening offer a side-by-side view of before-and-after effects for viewing convenience. This visual aid not only lets you see the sharpening effect, but also allows you to see how it affects attendant noise.
Here's a tip: Take note of where noise appears in the image. Does it appear in an area that doesn't have detail such as the sky? Does it appear in the shadows of the picture, normally with less visible detail? Do you lighten the shadows and see noise gradually appearing? What about noise that appears in the flesh-tone areas or among finer details? When noise is created, it appears throughout the image, but depending on the level of image detail and brightness in each area, the appearance will vary.
Here's another tip: Think about the idea of applying noise reduction and/or image sharpening selectively within an image. Setting up an adjustment layer in Photoshop CS3 allows you to use brushes to selectively apply sharpening or fight noise precisely. Nik Software's Dfine enables the selective application of many levels of sharpening within each image; again, my Nikon Capture NX software provides brush techniques that let me selectively apply Unsharp Mask at different levels throughout an image.
Night Scene In Snow
After this panoramic image was cropped using Photoshop CS3, I used Unsharp Mask to increase Amount (100%), which increased the sharpening effect (Figure 1). Make your selection by visually examining the effect in the preview window. Similarly, increasing the Radius (4.0 here) will spread the effect more widely over the pixels and increase the sharpening effect. Increasing the Threshold (100 here) will diminish the sharpening effect.
Choose a balance point between noise reduction, Unsharp Mask and the selections offered within the tools. Rest comfortably that you have visual access to see the effects from your changes.
For the same image, I applied Unsharp Mask at the indicated levels and uniformly across the image (Figure 2). Using the universal application, I noticed the appearance of some noise in the sky area. Considering that the image was made at ISO 6400 with such minimal available lighting, the low noise level is exemplary of what's possible with the newest imaging engine and attending technologies.
Taking advantage of nondestructive editing, I turned off the originally selected Unsharp Mask selection and replaced it with an Unsharp Mask Selective application (Figure 3). I selected the +Brush tool and applied the Unsharp Mask's settings to the dark areas of the image—the trees, fence and background landscape. Without the application of Unsharp Mask to the sky area, it appears much smoother and with less appearance of noise. Using the +Brush, this window's white area (Figure 4) reveals the underlying mask that illustrates where Unsharp Mask was selectively applied.