When I take photos, I like to be an invisible observer and not interfere with my environment. A vital part of that is to avoid using flash. Using a flash disturbs my environment and screws the natural lighting, as a result I use a number of techniquesto allow myself to capture photos in low light situations.
Reducing Noise By Downsampling
When the ISO performance is compared between cameras it is usually done at 100% blow ups of the original files, while this shows the actual noise in the image files it is misguiding. Most photos aren’t used at their maximum size, especially photos destined for the web will be significantly downsized. By averaging every pixel, the noise is averaged as well and less noise will be visible in the final image. Prints will benefit from this as well since a 300dpi print will work in the same way and average the noise. As a result all noise comparisons should be made at a predetermined target size which could be a 600×400 pixel image for the web or a 20x30cm print at 300dpi. This also means that if the photo will be used for the web or moderate print sizes it usually has about one stop extra ISO available.
A common problem when shooting in low light is the high dynamic range in the scene, thesmall light sources and objects directly lit are very bright and the shadows are dark. In order to extract as much dynamic range as possible without clipping the highlights and introducing excessive noise in the shadows it’s crucial too shoot .raw-files. The 14-bit files of current DSLR cameras can give up to two stops more dynamic range than 8-bit .jpg-files.Thepossibility to adjust the white balance in post production (since few cameras nail the WB in bad light) and the increased latitude to push it without clipping the saturation in individual channels is also important. Since sharpness is done at the target resolution (instead of in the full size .jpg) no halos are produced which degrade the result. A good start to experiment in Lightroom is to set Exposure to-1, Shadows to 0, Brightness to 70, Contrast to -50 and the Contrast Curve to Linear. Of course, the mood, feeling and values of the photo is far more important than one stop of extra dynamic range.
Even if the camera is set to tungsten lighting it often fails in cooling the color temperature enough when shooting indoors in moody, warm lighting. Photos from restaurant visits are easy to fix though, just use the white balance picker and click on a white plate. This will produce a neutral image which often feels sterile (since the lighting is warm from the start) so just drag the color temperature slider a little to the right to introduce some warmth in the picture.
The most visible noise in a photo is the blotches of chroma (color)noise. By keeping the luminosity information detail is preserved while visible noise is reduced. A similar effect and good tradeoff in Lightroom (since a .raw-file is used) is to set the Noise Reduction setting to 25 for Luminance and 75 for Color.Photos that need even more noise reduction can be processed in Noise Ninja or similar software where even more noise can be removed at a cost in detail.
Desaturating Photos and Black and White
The chroma noise can be pushed back even further by simply desaturating the photo or processing it to black and white. The remaining luminosity noise can actually be quite pleasing and give a documentary film kinda look. Of course, there’s limits when the noise just gets too harsh but this will give significant headroom.
The extended ISO range in camera is simply a digital amplification of the signal. A better way to do it is to set the max native ISO, underexpose a stop or two and then lighten the photo in post production since it provides better control. One stop of underexposure equals a doubling of the ISO, so -1 EV at ISO 1600 equals ISO 3200 and a DSLR with a maximum ISO of 1600 suddenly has ISO 6400 at its disposal without resorting to extended ISOs.