Ditching Dark-Frame Subtraction for Manual Noise Reduction

Even with the more modern cameras and advanced sensors, noise is still a big issue when it comes to dark long exposures.

Most cameras have Dark-frame subtraction – a mechanism which should handle noisy photographs. The way DFS works is by capturing a second photograph right after the exposure with similar conditions (ISO, shutter speed) so it can detect noisy pixels and adjust them.

Ditching Dark-Frame Subtraction for Manual Noise Reduction

But, as Jim Goldstein says, sometimes the camera cannot do that extra exposure. Either because it is a time lapse / star trail shoot where you don’t want to create gaps, or because the exposure is too long and the battery cannot handle another exposure.

…taking advantage of Dark-Frame Subtraction (DFS) isn’t always possible. If you’re shooting a sequence of images either for a night time-lapse or startrail photo DFS will introduce unwanted gaps or breaks. If you’re shooting extremely long exposures then your camera battery might not last long enough to complete your exposure, the dark-frame exposure and record the exposure to your memory card

Jim shares a technique where he uses a noise reduction technique in post. By overlaying two layers: the first is the original and the second is an almost identical layer but with Dust & Scratches filter applied. He then sets the blending mode to darken. The results are pretty impressive.

Ditching Dark-Frame Subtraction for Manual Noise Reduction

You can read the full process over at JMG-Galleries.

  • Hernan Zenteno

    Many thanks, this post was really useful for me.

  • thomas

    why not insted of one image create shorter multipul shots an use star-trails program to combine?

  • MikeN

    Why not use a dedicated dark frame instead. Cap the lens and viewfinder and do another exposure. This is then a record of sensor noise only. It can be done at any point before or after the primary exposure(s). This dark frame can then be subtracted from the primary image. It can be done in PS or any astro program such as Deep Sky Stacker.

  • kassim

    I prefer image averaging. In fairness, that’s the only technique that I know, hahahaha.

  • Debi

    Thank you! This is really helpful. Can’t wait to try it out.