Post Processing » Correcting Noise and Artifacts in Digital Images
My fine art printing work at The Center for Photography at Woodstock brings all manner of photographic work my way, from quiet still lifes to clamorous abstracts. It is, after all, Woodstock, NY and all Zen-like, I try to create a place of calm to do my printing. My walls are painted soothing 18% gray. My monitors are calibrated to a state of harmonious color balance and, if someone hadn’t stolen my favorite Enya tape, it would be playing right now.
But even with all my careful preparations, there are still times when my senses are attacked by shrieking sirens coming out of the darkness. Looking into the shadows I see only noise. It burns my eyes with apparitions of shape-shifting hue specters that wished nothing more than to torment my printers. Demonic digital artifacts taunt my mind's desire for smooth tonal transitions. Don't we all want smooth tonal transitions? I felt a need to cast out this offending noise from both my head and from fine art photographer Jared Handelsman's image, seen here:
As we stared at our first test strip under the D50 lights of our GTI Color Viewing Station, Jared Handelsman (an artist whose earlier work in photograms can be felt in his current work using a Canon Rebel to capture shadow play) and I stood transfixed like Quasimodo at the call to vespers. There it was, all over the dense shadows of his undulating, sinuous studies of shadow and form - Noise and Artifacts. I finally had to look Jared in the eye and ask him the question we both feared and embraced, “What ISO did you shoot this with, oh mighty Jared?” The artist returned my accusing gaze with steely conviction, “1600, I think.” Low light, long exposures and high ISO, a veritable breeding ground for shadow noise; Jared un-apologetically stated, “I needed it to capture the light.” These artists and their damn light, when I was his age we didn't need light. Shoulder to shoulder we strode into the clamorous fray.
Noise is there in most all of your digital images. You may not want to admit it, but it is. It is the nature of the electronic capture. When your sensor captures light, it creates this backdrop of noise, like the hiss you hear underneath a piece of recorded music or the snow on your television. In digital photography noise appears 3 separate ways - fixed, banding and random.
The Fix Is In
The noise in Jared’s symphony was primarily random. To heal this image, we would turn to the amazing filters of Adobe Photoshop's Creative Suite 5 (CS5). Certainly it would have been better if Jared had shot his work with a low ISO setting on his camera (the higher the ISO the more noise or digital ‘gain’ we see), or if he didn’t use such long exposures. Obviously we should shoot as we want, but, if I am forced to shoot at a very high ISO, I will keep that in mind as I compose my shots, allowing the grain or noise to become part of the mood of the image. If the noise is truly insurmountable, I find converting to black and white can heal a multitude of color sins. Deep in Photoshop's filter arsenal is the Noise Reduction filter.
Jared's pieces are nearly black and white, with vague hints of colors seeming to come and go like the shadows themselves. The noise was there and certainly converting the images to monochrome would heal them, but Jared did not want to convert to straight B&W. I couldn't blame him, the colors in his image are seductive hints of light that may or may not be there. The greater problems were my printer, a Canon ipf 6100, and my paper profile, Museo Portfolio Rag. They were picking up every little blotch and blemish the color gods threw up in the image file. I needed to reduce the color noise but not the tint. In the Noise Filter dialog box are 4 sliders; Strength, Preserve Details, Reduce Color Noise and Sharpen Details. I wish I could tell you the golden ratio that will exorcise all color demons, but each shooting situation can result in different intensities of noise. When I work with this filter, I work WYSIWYG - what you see is what you get. In this instance, I set Strength: 2, Preserve Details: 20, Reduce Color Noise: 75 and Sharpen Details: 50. I also checked Remove JPEG Artifact.
We held hands, chanted, “By all that is sacred and profane, I cast you out,” and applied the filter. The raging in my eyes and in my head subsided. Glorious silence. We still held the wisps of color that inhabited Jared's image, but the hellish hue hounds were heeled.
Now some of you may be looking at the images above and feel there is not much difference, well you’re just plain wrong. The image on the left screams, it rages, it is an affront to all that is holy. Its tinted taunts torture me.
I think I need to lie down now.