Sky/ground blending in images with subjects protruding above the horizon

Sky/ground blending in images with subjects protruding above the horizon

In addition to the mask for the sky, in Nebulb it is also possible to define a mask to improve the blending of those elements that protrude predominantly above the horizon.

How to define the mask for objects protruding above the horizon

Here are the steps to follow to create a specific mask for objects that protrude above the horizon, so that you can then apply different adjustments for the blending of these objects than for the rest of the image in general.

1. Activate mask for objects protruding above the horizon

Pressing the button in the upper toolbar with the image of a lighthouse (the one with the red arrow) activates the mask selection for objects that protrude above the horizon.

2. Select (roughly) the part of the objects that protrudes above the horizon (that which is above the sky)

Secondly, select the normal brush (red arrow) to define the mask for objects that protrude above the horizon (by painting directly with the mouse on the image). To define this mask in an easier and faster way it is often interesting to apply some zoom on the object to be masked.

IMPORTANT: As you can see in the previous image, to define the mask of the objects protruding over the sky you do not have to be very precise (it is a coarse mask). In fact, it is normal that when defining this mask, both the subject and part of the sky are selected. But there is no problem in doing so, because Nebulb has also the information of the sky mask, so that Nebulb can calculate this mask accurately internally.


3. Select (in a more precise way) the part of these objects that is in the ground area (in case the object does not start right at the horizon)

In case part of the object protrudes above the horizon and another part is on the ground, then it is usually convenient to mask the part of the object that is on the ground as well. But, unlike in the previous step, now it is necessary to be more precise in the definition of the mask and just select the object (nothing else).

IMPORTANT: To define the mask in the area where the object is on the ground, it is necessary to be more precise (it is not necessary to be super accurate in the selection, but try to make it close enough). In this way, the blending of this object with the rest of the image will be as natural as possible (both in the part that is on the sky and on the ground).

4. Refresh the masks

Once you have completely masked the objects that protrude above the horizon, press the refresh masks button (red arrow) so that Nebulb can use the new mask during the sky/ground blending adjustment.


Adjust specific blending for objects protruding above the horizon

By defining a mask for objects protruding above the horizon, Nebulb allows you to independently adjust the sky/ground transition on these objects.

To do this, simply press the button on the right (the lighthouse image) at the top of the "Blend" module:



Pressing this button displays the same controls as for general sky/ground blending, but they can be set to different values. That is, different adjustments can be applied for the blending of objects above the horizon than for the general blending of the sky with the ground in the rest of the image.



Example 1: Small objects

The way of adjusting the sky/ground blending when masking some object protruding above the horizon is practically the same as in a normal image, except that it is done in two stages:
  1. First the sky/ground blending of the overall image is adjusted (without taking into account the object protruding above the horizon). Here the idea is that the sky part is well integrated with the ground of the entire image (as if the protruding object did not exist).
  2. And secondly, the blending of objects protruding above the horizon with the sky is adjusted.
By making these two adjustments, all the elements of the image (sky, ground and protruding subjects) are perfectly integrated and the whole image is perceived as natural.

Here is a practical example of how to adjust the sky/ground transition in an image with a (relatively small) object protruding well above the horizon:

1. Result with default settings

In this case, with the default settings you do not get a very good initial result, since both the horizon part and the protruding object do not integrate naturally with the sky. Well, as always, the first thing to do is to start adjusting the general blending of the sky with the ground, for which you have to press the button with the red arrow.

2. General sky/ground blending: Adjusting the sky transition

Increasing the radius and a little bit the hardness of the sky transition enlarges the transition zone of the sky and makes the blending of the horizon look much better.

3. General sky/ground blending: Adjusting the exposure balance

The exposure balance is reduced a little to slightly decrease the brightness in the horizon area to better balance it with the rest of the sky.

4. General sky/ground blending: Adjusting the ground transition

The radius of the transition zone of the ground is reduced to make this zone narrower and thus make the initial part of the coastline maintain a similar brightness to the foreground. At this point, except for the tree trunk that has a weird glow around it, the sky/ground blending in the rest of the image is already perfect (everything looks very natural).

5. Blending of objects above the horizon: Adjusting the sky transition

When enlarging the image around the object protruding above the horizon you can better appreciate the weird glow around it. To start adjusting the blending of this object the first thing to do is to select the particular settings for the blending of objects protruding above the horizon (red arrow).

In this case the adjustment of the sky transition has been limited to simply decreasing the opacity and, with that alone, the blending of this object on the sky has been greatly improved.

ADVICE: When adjusting the sky transition for objects that protrude above the horizon, it is usually very effective to decrease the opacity, since this alone makes the object blend super well into the sky. There are cases in which this may not be the case (because the blending issue depends a lot on each image), but it is something that usually works in many occasions.

6. Blending of objects above the horizon: Adjusting the ground transition

As in this case the object is very thin, the radius is decreased so that the size of the transition is better adapted to the size of the object. In addition, the hardness is slightly increased to highlight a little more the volume of the tree trunk (through these side shadows).

7. Blending of objects above the horizon: Adjusting the exposure balance

Finally, it was decided to decrease the exposure balance a little to darken the trunk slightly so that it is better integrated with the illumination of the rest of the ground.

Final image obtained in which all parts of the image are blended in a very natural way.



Example 2: Large objects

Here is another practical example of how to adjust the sky/ground transition in an image where there is an object (in this case a very large one) protruding above the horizon:

0. Define the mask for objects protruding above the horizon

As in the previous example, you must always first define the mask for objects that protrude above the horizon. Notice how, as before, when masking the tower, it is done roughly in the area above the sky and more precisely in the area where the tower is on the ground.

1. Result with default adjustments

This is the result obtained with the default blending settings and, as you can see, an unnatural glow appears between the ground and sky elements, which we must remove to make the image look natural.

2. General sky/ground blending: Adjusting the sky transition

First of all, the radius of the sky transition is increased to make it larger and also the opacity is decreased to make the blending of the trees in the background more natural (it usually works well to reduce the opacity of the sky when there is vegetation on the horizon).

3. General sky/ground blending: Adjusting the exposure balance

The exposure balance is reduced by half a stop (-0.50) to equalize the brightness of the horizon with the rest of the sky.

4. General sky/ground blending: Adjusting the ground transition

In this case, both the radius and the hardness of the ground transition are increased to make the illumination behind the trees look the same as the rest of the sky.

5. Blending of objects above the horizon: Adjusting the sky transition

Once the adjustments for the general blending of the sky with the ground have been made, the next step is to make the specific adjustments for the blending of the objects that protrude above the horizon (the tower in this case). As always, the sky transition is adjusted first. In this case the radius has been increased and the opacity has been reduced to make a wider and more blurred transition area, so that the tower blends in very well with the sky.

6. Blending of objects above the horizon: Adjusting the ground transition

Finally, the radius of the ground transition is slightly enlarged to make the tower illumination a little softer.

7. Blending of objects above the horizon: Adjusting the exposure balance

In this case it is not considered necessary to apply any change of exposure balance, so the image obtained in the previous step is considered definitely finished.

Also, below you can check in more detail the sky/ground blending obtained, thanks to which the final image is perceived in a very natural way (no lighting discontinuities anywhere).







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