Even with small color and luminosity variations you can get great results!
To realize this photo I took 42 shots using a C8 telescope, a focal reducer (f6.3) and my canon 7d.
These are the shooting condition:
Iso 100, 1/400 sec, raw @ 16bit with every parameters at 0, color profile Adobe RGB.
I deliberately over exposed, without clipping the white, for 2 reasons: to increase the signal to noise ratio (SNR) and to communicate the feeling of high luminosity typical of a full Moon.
In order to further reduce the noise, I made an average of 36 shots with Registax. The noise reduction is equal to the square root of the shots’ number. Thus 36 shots lead to a noise reduction of 6 times (fig1).
Moon average fig1Moon average
These two points are reasonably neutral but it is difficult to find a grey point on Earth’s satellite. I looked on internet for more images of colored Moon in order to find a place where the saturation normally is very low. So I placed a color sample close to Kepler crater (point 3).
These are the RGB reading:
Point 1 (highlight): 242, 241, 239
Point 2 (dark shadow): 21, 20, 19
Point 3 (grey): 200, 197, 191
These values tell us that the shot is affected from a reddish hue likely coming from the light pollution of the city mainly in the quarter tone. After modifying every single channel by means of a layer curve, I got the following result:
Point 1 (highlight): 241, 241, 241
Point 2 (dark shadow): 20, 20, 20
Point 3 (grey): 197, 197, 197
About this choice we can say different things: are the identified terrains really neutral? Is the sky neutral or do I need to leave a bluish hue? I believe that no one knows the right answer, but what is really important is that the final result is pleasing and believable. After the color correction we obtain fig2.
Moon after color correction fig2Moon after color correction
Luminosity and contrast
First I applied two unsharp masks (UM) in order to keep a better control on highlights since I am going to use a curve to improve luminosity and contrast. This is the workflow:
USM mask fig.3USM mask
USM inverted mask fig.4USM inverted mask
This mask will block the pixels with a luminosity higher than 240 coming as a result of the UM.
At this point we are ready to improve luminosity and contrast as follow:
Luminosity curve fig.6Luminosity curve
Boosting colors and creating color variations
To boost the colors and to create color variations I used two well-known technics from Dan Margulis:
The Modern Man from Mars and the Color Boost both launched by the Dan Margulis’s PPW panel (free download from internet).
Boosting colors fig.7Boosting colors
I changed the followings settings in the layer structure that can be seen in fig.7 as result of CB e MMM action:
The idea behind these steps was to create a general harmony in cold and warm hues leaving a natural aspect: a Moon living between a greyscale and a colored image.
To emphasize the lunar seas:
At this point I slightly applied the cutter tool to the lower border and removed an artifact of the UM.
To leave a feeling of neutrality even being a colored image:
Further adjustment can be achieved:
Here is the final result compared to the original file.
A colored moon before-after fig.9A colored moon before-afte
Final thanks go to my friend Salvo Lauricella and to his telescope!!!!! And to the Color Correction Campus group on Facebook.
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!!