Even with small color and luminosity variations you can get great results!

Shooting conditions

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).

Color correction

1. I locate the light point close to Tycho crater placing a 3x3 color sample (point 1)

2. then the shadow point in the sky (point 2).

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.

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:

1. Duplicate the layer background;

2. On the new layer, apply an Unsharp Mask (UM): amount 500, radius 2, threshold 0;

3. Rename the layer UM;

4. Apply a layer mask to it

5. and a new layer threshold: amount 240 in order to put in evidence the pixels with a luminosity higher than 240 (Fig. 3).

1. Apply the inverted merged result to the mask in the layer UM using the command “apply image”

2. With a further Gaussian blur with a 1 or 2 pixel radius;

3. At the end de-select the threshold level (Fig. 4).

This mask will block the pixels with a luminosity higher than 240 coming as a result of the UM.

1. Stamp visible;

2. Repeat the process with a new UM: amount 500, radius 1, threshold 1 (fig.5).

At this point we are ready to improve luminosity and contrast as follow:

1. Apply a layer curve in luminosity mode to move the shadow point to 10,10,10 using only the green channel;

2. Apply a second layer curve in luminosity mode to increase the contrast and reduce the overall luminosity (remember that I overexposed the shots) using a classical S curve on the composite RGB (Fig. 6);

3. The shadow point now measure 0,0,0.

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).

I changed the followings settings in the layer structure that can be seen in fig.7 as result of CB e MMM action:

1. MMM color – mask: density to 30% to increase colors variation;

2. MMM color – mask: with black brush I blocked a blue/magenta halo in the border generated from the chromatic aberration of the telescope;

3. Color boost: opacity to 50% to increase color saturation;

4. Color boost – Mask: created from the b negative channel of Lab to selectively reduce color saturation in the blues.

5. End point adjustment: increasing warm colors by slightly moving the curve in the a and b positive channels.

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.

Last retouch

To emphasize the lunar seas:

1. Stamp visible;

2. Apply an inverted UM or HIRALOAM on the upper layer with: 50 amount, 30 radious, 0 threshold ;

3. Apply a mask created from the inverted Luminosity channel;

4. Blur the mask with a radius of 20-30 pixel;

5. Apply a noise reduction: amount 5 in luminosity and 100% in color;

6. Apply again a mask created from the inverted Luminosity channel;

7. Blur the mask with a radius of 20-30 pixel;

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:

1. Stamp visible;

2. Apply a layer saturation: amount -40;

3. Apply a mask from the inverted luminosity channel (or RGB) in order to de-saturate the lighter areas (fig.8)

Further adjustment can be achieved:

1.  Increasing saturation to the merged layer only into the warm colors.

2. Applying an UM: 250 amount, 1 radius, 10 threshold with a mask (same workflow described in the beginning).

Here is the final result compared to the original file.

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!!

Ciao

Dario