Exposure stacking of a moonlit landscape - a challenge in Photoshop

 

You may have tried this yourself, trying to photograph a nice landscape with the moon during the twilight hours in the evening or morning. For a landscape like this you need a tripod and a long exposure time. The moon being many times brighter needs a very short exposure time. In cases with such brightness differences you normally make an exposure series as shown here (with tripod!) and use high dynamic range techniques and exposure stacking which is nowadays quite straightforward to use. However with the moon and a bright planet (Mars, or Venus) below the moon this does not work for several reasons:

• The long exposure gives 'stripes' for the stars, planets and the moon as well, because the earth moves
• Even more problematic for the same reason is that the moon, stars and palnet change position across the image between exposures
  
• The exposure difference is too extreme. Even stacking the cropped moon alone with over 10 images does not yield a nice image

As I will explain here, there is a 'dirty' solution to this problem, which is not as realistic as exposure stacking, but gives a result that is quite true to the experience of the viewer. In short: the washed out moon needs to be cleaned (and not as bright), as well as planets and stars visible as stripes. From the end of the exposure series you copy in a layer and set it to blend mode 'lighten'.

I choose the second image of the stack to start with because it has the nicest landscape exposure. I do not need more highlights or better exposure in any other region than the moon and other bright objects.
For the moon I use the elliptical marquee tool to select the area that is too bright. With the patch tool I drag it to the blue area next to it and Photoshop tries to cancel it out. Here I did it twice, and you may also want to darken it more and change the color balance from blue to yellow (I did it as final tweak in the end). The spot needs to be darker than the moon from the last image in the exposure series. Similarly I used the lasso tool and patch tool for the bright stripe below the moon. On the right image above you see the corrected version.

With this challenging exposure series, before continuing with our 'main image' we need to combine the last two images of the exposure series as well. We take the second last and do the same for the moon as before (the planet is a dot already, no change needed), resulting in the image on the right (note that I did not brighten the image, this is an optical illusion! Left and right are equally bright).

From the last image I copy the moon and paste it as a new layer in the edited image. I set the blend mode to 'lighten' separating the moon nice and clean. Now I select (from the merged image) the moon and the planet and go back to the main image.

I paste the moon now as a new layer and set the blend mode to 'lighten'. In this case it works for the planet, but not for the moon. Therefore I copy the layer again and use masks to separate the moon and the planet. I need to lighten the moon to make it work. The result is in the right image. As a final touch I lightened with masks close around the moon.

The final image

I have another example that was considerably easier to do, with only two exposures needed.

The workflow is the same. In this case I did not have a planet, stars or a complicated exposure series. Here the technique makes a nice moon-haze that is dark enought to bring in the well exposed moon. Exposure series with a tripod have the advantage that the size of the moon is exactly right. Although it is not 'exactly as seen', because a part of the haze is fake, all other parts of the image were taken at the same place and time.

The resulting image!