While editing some landscape shots with stars, I tried to use darkframes to reduce the noise.
More precisely, my approach was to take a series of shots, then firstly to subtract dark frames from each shot, secondly to use the mean of the series for the foreground to further reduce noise, and thirdly to use an astro stacking tool (Sequator) to stack the sky.
Instead of reducing noise, the darkframe subtraction:
- increased the noise- or rather, added some dark/monochrome noise.
- changed the white-balance/tinted the image.
I do not understand why this is happening/What I am doing wrong.
All photos were shot in succession, with the same settings (15sec, @ISO6400, in-camera dark frame disabled).
All photos were shot with the same white balance.
While shooting the darkframes, both the lens cap and the viewfinder cover were applied.
Photos were imported from my Pentax K1ii, converted to DNG in LR, and exported to PS without any editing/import presets applied.
I used PS, placed the darkframe layer(s) above my picture, and used the subtract blending mode.
I followed basic instructions found here/in various videos on dark frame subtraction in photoshop. Note that basically, all of those cover dark frame subtraction with one frame (or use tools other than photoshop). I have tried both using one, and 3 frames. The results are similar, albeit more pronounced with 3.
I used the free tool "sequator" to subtract darkframes instead (and to align stars). Adding the dark frames here made absolutely no difference.
A crop of the first picture, with (3) dark frames subtracted:
A crop of the second picture, without dark frames subtracted: