A small side-step from the main path
The tutorial "A colored Moon" described how to improve colors and luminosity when shooting at the full Moon. If you follow every single step it would be easy to achieve more or less the same result I illustrated.
In that case, the Moon lived in the quarter of tone and was easy enough to apply a luminosity curve adding contrast only to the Moon but not to the background (fig.1)
contrast curve fig6
Infact, the background lives on the left side of the histogram and the Moon on the right side; nothing stays in the middle where the curve starts its effect (fig.1)
When you shoot at the a "not Full Moon", things get more difficult since the areas close to the terminator tends to get darker and darker until they fade into the background.
This means that it is not possible to isolate the sky from the Moon any more. As can be seen inside the red circle of fig.2, there is no gap between the dark pixels of the sky and the ones of the Moon.
luminosity curve without mask fig.2 - Luminosity curve applied to the moon without luminosity mask fig.2
In this case, if we apply a "S" curve to reduce luminosity and to add contrast, as we have done in fig.1, there could be the risk to close the shadow and reduce the contrast losing a lot of important details (see fig.2 getting darker on the left side). Not to close the shadows means, in such a situation, not to move the shadow point. This will result also in a less deep curve in the 3/4 of tone (look at the curve inside the red circle of fig.2). We remember that: "the deepest the curve, the more the contrast!"...and vice versa.
Then, to achieve our goal, that is to increase the overall contrast without losing important details, we need to protect the darkest area with a mask.
It should be dark in the darkest area and light in the lightest area. Despite the fact that it could appear as a joke, this is the reason why we need a mask right from the luminosity channel whose result, along with the luminosity curve effect, can be seen in fig.3!!!!
Luminosity curve applied to the moon with luminosity mask fig.3 - Luminosity curve applied to the moon with luminosity mask fig.3
Now the overall contrast is improved but we have not lost details close to the terminator. Even the histogram (inside the green circle) show us that the curve will not modify the darkest areas.
At this point, we are ready for the Color Boost and MMM action of Dan Margulis's PPW and the result is shown here after removing the mask in the MMM color Layer and increasing the opacity up to 50% (fig.4).
Moon MMM and CD fig.4 - Modern Man from Mars applied to the moon from dan Marguilis's PPW
Now we need a saturation mask to protect the "Moon" from this explosion of colors:
1. Create a white mask in the MMM color layer
2. Apply the a channel from the merged layer
3. Apply the b channel from the merged layer in lighten mode
4. Apply the inverted a channel from the merged layer in lighten mode
5. Apply the inverted b channel from the merged layer in lighten mode
6. Auto tone
7. Invert the result and apply a curve to modify the contrast
8. Blur the result
this is the final saturation mask (fig.5) which is dark where the saturation is higher:
saturation mask fig.5 - saturation mask
At this point, by moving the mask density, you can decide how much color and color variation should be applied in your workflow (fig.6).
mask density fig.6 - mask density
The Moon needs final adjustments such as: removing the cyanish halo, adjust the detail with unsharpening process and so on. This is already described in the first tutorial.
Do not forget that even the best shot you can do will not compete with the nature show itself!!
If you think that this Tutorial could be useful to other astronomy and astrophotography amateurs, please feel free to share it!!
Paint the Sky, Share your Knowledge!!
Ciao
Dario