Today’s Question: I would like to know the difference between the long exposure noise reduction option in camera and the noise reduction with Lightroom or Photoshop. What is the best option for long exposure with a 10-stop ND filter?
Tim’s Quick Answer: These two types of noise reduction are actually fundamentally different, with the in-camera option relating to how the camera actually behaves while the post-processing option can only analyze pixel values in the photo. For long exposures I recommend employing both in-camera and post-processing noise reduction.
More Detail: The in-camera noise reduction option provides a unique advantage, in that it is able to compensate for the actual behavior of the image sensor at that specific time under the current conditions.
As you may be aware, there are a variety of factors that can impact overall noise, including the design of the image sensor, the duration of the exposure, and the amount of heat buildup on the sensor. In-camera noise reduction provides the best opportunity to compensate for these various factors. In most cases this function operates by essentially capturing two exposures. First, your actual exposure is captured. Then a “black frame” is captured, where a photo is captured with the same exposure duration, but with the shutter closed to prevent light from reaching the sensor.
This black frame exposure can then be used to determine the noise behavior of the image sensor under the current conditions, so that the camera can then process the actual capture to subtract out the noise. This is, of course, a rather sophisticated operation, and it can be very effective at reducing the noise in the initial capture.
When you are applying noise reduction in post-processing, you only really have the pixel information to work with. Thus, noise reduction software uses a variety of techniques to evaluate and reduce the appearance of noise in the photo.
Since both in-camera and post-processing noise reduction employ a different approach to reducing noise, and since they compensate for different limitations, I recommend using both of them. I generally consider in-camera noise reduction to be the more important of the two, but there will likely be some degree of problematic noise remaining in the image even after in-camera noise reduction has been applied. The careful application of additional noise reduction in post-processing can help ensure the best image possible from the perspective of noise.