I want to take a picture of a very dark scene with the help of all the noise reduction tricks you would use when shooting stars: stacking multiple exposures, using dark frames, bias frames an so on.

In other words: I want to do manually what Deep Sky Stacker does (appart from the alignment which is not necessary); but cannot use DSS because there are no stars in the image..

What are the steps it takes to combine multiple frames into one shot (with better SNR) and how do you perform those in PS?

  • \$\begingroup\$ Hey Smow, I don't generally shoot astro and not sure about the dark frames, frame bias, or anything about Deep Sky Stacker. From what I gather Deep Sky Stacker is a stand-alone app. Now you want to be able to do noise reduction in Photoshop? Would that be correct? If so I can make a tutorial that may help you. But before I take time to do that (I'd have to also shoot some noisy shots to use) could you let me know exactly what you're going to be looking for. \$\endgroup\$ Commented Jan 23, 2017 at 14:37
  • \$\begingroup\$ @RyanFromGDSE: Suppose I have two underexposed images in two layers and aligned. What type of blending would you use to enhance SNR and brightness? \$\endgroup\$
    – Crowley
    Commented Jan 23, 2017 at 17:39
  • \$\begingroup\$ What Crowley said, also: What type of blending would you use to utilize dark frames and bias frames to further enhance SNR? (as far as I understand, dark frames are to reduce fixed pattern noise, bias frames can reduce read noise, layering of multiple light frames aims to reduce random shot noise.) \$\endgroup\$
    – smow
    Commented Jan 23, 2017 at 22:38

2 Answers 2


Assuming all the layers are aligned correctly, if you select them all and create a smart object, then with it selected select layer/smart objects/stack mode/median.

For dark frames use blending mode subtract for the layer, but you would need to do this for each image before stacking them.

With modern DSLR you probably don't have much need of dark frames though, just stacking will be enough.

Hope that helps.


I would suggest layer/smart objects/stack/summation, rather than median.

  • 1
    \$\begingroup\$ Can you expand on this answer? The OP asked for what steps to take to combine multiple frames, and then clarified in the question comments that they also wanted to use dark frames / bias frames to further reduce SNR. \$\endgroup\$
    – scottbb
    Commented Dec 16, 2017 at 13:57

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