How to Fake Noise Reduction: Black and White Conversion

Restys-Que Caro-Josh Netsky, Valentines, Albany NY

I checked out a show at Valentines with Restys, Josh Netsky, and Que Caro, bringing the camera mainly so Mikey wouldn’t feel so self conscious about having his. I’ve shot there before so I knew what to expect: lots and lots of dark. If you don’t bring your own light (i.e., a flash), you’re going to need a lens with a wide maximum aperture to get usably fast shutter speeds. Where normally I’d grab the Canon 50mm f/1.8, this time I threw on an old manual Pentax SMC 50mm f/2.0, from an old film camera, using an adapter. Yes, it’s about a half stop slower, but I also knew that in the low light my autofocus would be stubborn, and I’d end up manually focusing. The old lenses were made for manual focus in ways the newer ones aren’t, specifically with a nicely generous long throw on the focus ring.

I ended up in manual exposure mode, pushing the ISO as far as my camera can go (to 3200), leaving the lens wide open, and dialing in at 1/30th of a second shutter speed. This is still a very slow shutter, but when shooting bands there are usually plenty of moments when people are standing relatively still — or holding onto a note, like Caroline is above. The slight motion blur at other times can actually be pretty pleasing. Now, to give you an idea of how dark this place is, you can usually shoot on a sunny day at f/16, ISO 100, 100th of a second shutter speed. The difference between f/16 and f/2 is six stops, ISO 100 to 3200 is five stops, and 1/100th to 1/30th is just shy of two stops. That’s a thirteen stop difference — in other words, you could say this was darker than a bright day by a factor of thirteen, or 169 “times” darker. Without the ability to go to high ISO sensitivities or wide apertures, you have to keep dropping the shutter speed, which is why many cameras just can’t give results in low light. If my lens were f/5.6 at the widest, the shutter speed would drop to an unusable 1/4th of a second.

Restys-Que Caro-Josh Netsky, Valentines, Albany NY
a little motion blur won’t hurt anyone

That’s not what I really want to talk about though. You’ve seen the kind of noise I get from ISO 400. 3200 is really not pretty, people look like they have a rare skin disease, large regions of black look like tiny gnomes are setting off tiny fireworks everywhere, it’s a disaster. Even the best noise reduction software struggles to correct it, and when it does some sharpness is lost. But there’s a sneaky way around this; it doesn’t totally solve the problem but it makes otherwise trash photos usable.

It has to do with the fact that there are two types of digital noise: chroma and luminance. Chroma noise is random bits of color thrown in somewhat evenly throughout the photo, most noticeably red and blue. Sometimes it’s not much of an issue, but when you have areas of fairly solid color and especially skin tone it quickly damages a photo’s quality. Luminance noise is a simple lightening or darkening of color information, and even at moderate levels it’s doesn’t degrade quality too much. In fact, luminance noise is often compared to monochrome film grain (in a good way), which is where our trick comes in.

Yep, since black and white film grain is usually seen as wholly acceptable, we’re going to make this noise look as much like it as possible. That means converting to black and white.

There are a lot of different ways to convert to B&W, and I’m not going to get into all of them. Most importantly for my purposes here is to make the conversion a very late step in overall processing. A typical quick processing flow for me goes something like this: correct exposure and white balance plus any cropping in RAW, export, adjust curves for contrast and saturation, desaturate individual color channels and touch up errors (sensor dust, etc.) if necessary, denoise if necessary, sharpening and save. In the case of B&W conversion, it’s almost identical except that when denoising, I’ll first only correct chroma noise. Even though I’m turning it grainlike, I want it under control, and correcting chroma noise doesn’t hit sharpness too hard. I then convert to B&W by using the channel mixer, selecting monochrome, and adjusting the color channel sliders individually. I then denoise again, this time bringing luminance noise down to strike a balance between “grain” and sharpness. I’ll skip a sharpening filter here because that will tend to simply re-emphasize the noise I removed.

The result isn’t going to win any awards, but it’s way better than having no photo at all because of really ugly noise all over everyone’s face. I don’t hate anyone enough to push out photos of them looking like that, let’s be a little bit kind to our subjects, right? I had a lot of trouble focusing, and for me the end lo-fi, grainy, soft, sometimes slightly blurry result works alright.

Anyway, it was a great show, Valentines is really doing good things by bringing in these more obscure bands for $5. Even if it’s not exactly your thing, that’s what, two cups of coffee? Here’s a couple more and there’s a short slideshow.

Restys-Que Caro-Josh Netsky, Valentines, Albany NY Restys-Que Caro-Josh Netsky, Valentines, Albany NY
Restys-Que Caro-Josh Netsky, Valentines, Albany NY Restys-Que Caro-Josh Netsky, Valentines, Albany NY Restys-Que Caro-Josh Netsky, Valentines, Albany NY

PS: I’m glad I gave Mikey the backup. The audience was apparently afraid to get any closer than twelve feet from the stage, so we were these guys with big cameras walking around, picking our angles, and generally being in front of things whereas I’m used to being in the crowd, a part of it. In this case, you just gotta be confident, and be conscious of annoyingly blocking anyone’s view for too long or getting in the way of anyone else taking photos or recording video. So there’s that.


One thought on “How to Fake Noise Reduction: Black and White Conversion

  1. Raj

    I found this post because I use the same trick and was looking to see if it was fairly well known or suggested on the Internet. Yours is a great workflow for this effect. I hadn’t considered denoising chroma and luma separately to maintain sharpness, that’s a genius insight. I had been denoising both channels, and living with the extreme softness as an artistic choice.

    The lighting difference you talk about is also a lot worse than you think; 13 stops isn’t 13^2 times less light, it’s 13 halvings of light, which is 2^13, or 8192 times less light!

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s