How can I avoid grid noise / read noise

Question

I have read a bit about this subject (Read Noise) and to be honest I rather shoot at ISO 100 for the finest detail and maintain the scene as I see it. Example .. I shot a fishing pier after sunset with a 3 stop ND filter and a clear night filter on a nikon D800e f/11 and started at about 2 1/2 minutes, and as it got darker I increased exposure time.the idea was to covert the image to B&W and leave it dark as My eye's saw it. there was some moon light and a couple lights on the pier which gave it some interesting contrast. I made 7 images with out moving the camera or focus, just longer exposures. The results when importing them into lightroom were interesting but when I zoomed in at 1-1 or 2-1 there were the faint grid lines, vertical seemed more pronounced, also had hot white pixels but dust and scratches filter in PS took care of those. I understand the concept of letting in more light/longer exposure and maybe a higher ISO say 800 or 1000 and then once in lightroom drop the exposure and maybe work the noise slider a bit. I will have to try this and see how it turns out. Any suggestions would be greatly appreciated. TY

Answer 1

There are really only two viable options to your problem:

• Increase the amount of light entering the camera in amounts proportionally higher than the amount of read noise introduced by thermal issues associated with longer exposures

or

• Use a different camera that produces lower read noise for the same exposure conditions

If you allow more light into the camera which makes your image brighter than you wish, then you can reduce the brightness in post-processing which also reduces the amount of read noise by the same proportion.

Many movies that show "dark" scenes are shot in brighter conditions and then darkened in the post-processing phase of production. Even with chemical film the development could be altered to make the rendered scene darker than it was shot, or they could even develop the original normally and then darken the positives that were made from the original edited (edited in the sense of cutting out and splicing lengths of film to remove parts of the footage and to sequence the final result differently than the order in which it was shot) film. This question here at Photo SE addressed that very topic:

Why are my low light photos noisy /blurry, but Alien is perfect?

Using low ISO doesn't have much of an effect on noise if you let only the same amount of light into the camera as you would have at a higher ISO and using the higher ISO is not blowing out any highlights. When you boost the exposure in post, you'll also boost the noise. Noise reduction algorithms are getting better and better, but they still have a problem with fixed pattern noise because it looks like image details instead of randomly distributed darker and lighter pixels.

Answer 2

Typically this grid effect is worked around using an technique used often in astrophotography. The technique is called "stacking", and gathering bias frames will allow specialized software (some of which is free) to subtract this noise from your image.

The benefit here is that you may be able to rescue your images by taking a series of frames following the guide linked above.

• Use the fastest shutter speed possible (often 1/8000″)
• Keep the lens cap on your camera or telescope (and cover the viewfinder)
• Use the same ISO as your light frames
• Capture about 20-40 bias frames

Load these into software - I prefer DeepSkyStacker - and let it chug through your images. There's a slight learning curve here but the end result is almost always a completely noiseless image with high detail.

Answer 3

The proverbial elephant in the room regarding read noise is of course the 3 stop ND filter. The recipe for "less read noise" is "more light", and an ND filter makes for the opposite.

Touching anything else is a distraction and putting lipstick on a pig regarding your current setup.

Of course, ISO100 as the lowest ISO for a 36MP CMOS-sensor camera (from 2012) means that the camera will have a higher photon noise level to start with than some other cameras designed with lower noise in mind. Particularly since your camera has no antialiasing filter, reducing the resolution for reducing noise should also be a workable option. I have no idea whether this camera's sensor uses microlensing to increase the photon yield.