We see and photograph reflections of light from the surfaces surround us. If objects did not reflect light we would not see them. Upon reflection, however, the quality of the light may change with undesirable side effects for photography. Before it reflects from a surface, light wave moves in all directions very much like a pipe cleaner with its bristles coming out in all directions. When it reflects from a surface, depending on the angle, reflective surface qualities, our angle of observation, the part of all of the light may become polarized. A polarized light wave no longer moves in all directions but in one direction much like a recording tape, flat.

What is a polarizing filter

When polarized light hits the camera lens, and consequently the film or the digital sensor, it records only as a shiny reflection and we do not see the surface from which it reflects. In order to see the surface, we need to remove the polarized light so the non-polarized light could record an image of the actual surface, say water or display window. A polarizing filter performs this task depending on many factors. By rotating it, we bring its “light grill” so to speak perpendicular to the polarized light direction and it cannot pass through the filter, the lens and record the reflection on the photograph. To visualize the concept, hold your hand out with fingers close to each other but not touching, call this the polarizer. Then, take a crisp dollar bill, call it the polarized light, and slide it through your fingers. Now, hold the angle of the dollar bill and rotate your hand, presto, you have created a “dollar polarizer.”

How does it work

Now, this is how it works. But it does not work all the time and at all angles. First, it only works for light that reflects off nonmetallic surfaces. It is not going to do much to remove the reflections from the stainless-steel kitchen sink. Second, it depends on the angle of the light hitting the surface. Light gets polarized when it hits a surface at a particular angle. (I am not a physicist, so I am probably sticking my neck out here, but I think that angle is 26 degrees.) The effect of a polarizing filter depends on the angle of rotation with respect to the camera lens, thus, the incoming light. If the angle is perfect, it may totally remove the reflection and you could see the fish swimming under water. Otherwise, the effect will be partial or even nonexistent.

How to use it

A polarizing filter is very useful in many photographic situations but it really comes to its own in outdoor, nature, and landscape photography where lighting cannot be controlled. Under outdoor lighting practically everything reflects the blue sky and thus lose part of their color depth. A polarizer may remove the reflections on the leaves and make the foliage really show its true color. Reflections on water could be very dramatic if planned or they could be very distracting if polarized light interferes with the photograph. Again, a polarizing filter could remove some or all of the unwanted reflections.

Perhaps, the most common use of a polarizing lens is to deepen the color of bright blue sky, like those you would see on a crisp day. Here, there is literally a “rule of thumb” to use to figure out where the maximum polarizing will occur in the blue sky. As you stand outdoors, under the big blue sky, hold your hand out with only the index finger and the thumb extended. Now, make the index finger and the thumb form a right angle as if you are imitating holding a gun and point your thumb at the sun. Now, when your rotate your hand around the axis of your thumb, your index finger will draw an arc in the sky where maximum polarizing effect will show. The effect will be quite dramatic if the sky happened to have a few decorative white clouds against the blue sky.

May your light always come from the optimum angle.

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How it works

Digital polarizer works by mimicking the features of a real polarizer. The technique works best with photographs with blue skies or blue ocean and some unwanted reflections on water. I have successfully used it to achieve richer colors even without any part of the sky showing. The reason it works is very simple. Even though the sky may not be visible as part of the image, its reflection on most surfaces is there as a slight cast of cyan. So, by removing it we can clean other colors of this invisible haze.

Step-by-step

I will start with an image with a large area of what was supposed to be blue ocean. Feel free to copy this image and practice in Photoshop. I photographed the swan at a nearby cove and the water was indeed a nice shade of blue.

I roughly adjusted the curves to get the swan image I wanted. I did not do any color correction in red, green, or blue channels. Now comes the fun part. When I look at this photograph, I want to see the water as blue rather than bluish gray. This tells me I need to work with the “neutrals” and the “blues.”. Now is the time to add a “Selective color” adjustment layer. Either use the shortcut from the bottom of the “Layers” panel or follow the menu options “Layer/New adjustment layer/Selective color.” Using the drop-down color channel selector, click on “Neutrals” and move the sliders as shown below. You may write the numbers if you wish.

Figure 2 Neutral Channel

Each slider here represents primaries and their opposites. Cyan-Red, Magenta-Green, Yellow-Blue sliders add to the labeled color in the positive direction and add to the implied color in the negative direction. So, -29 yellow is +29 blue and so on. After checking the numbers click on OK and look at the image if you are following the tutorial in Photoshop. It should look like the following image.

Figure 3 After Adjustments

We added more blue, more cyan and more black to the neutrals. It looks better than the original but we are not done yet. Now, double click on the selective color channel and this time select “Blues” from the drop-down list. Now we will adjust the blues to the values shown below.

Figure 4 Blue Channel

Adjust the values as shown and click on OK. These adjustments will add to the blues more cyan, more blue, and more black. The result will appear as follows.

Now, I have a pretty close shade of blue for the ocean but I have introduced a bluish tint to the white feathers of the swan. This can be fixed by changing the blending properties of the selective color channel. Right click on the selective color channel and select “Blending options” from the pop-up context menu. We do not want the adjustments we have made in the selective color layer apply to whites. So, we move the slider as shown below.

First move the highlight triangle to the left until you read 190. Then, while holding the Alt key (on PC) click on the left half of the triangle and move it to the left until it reads around 167. This is not an exact number. It simply provides a smooth transition of the effect between that range of brightness. The finished image will have clean whites on the swan and deep blue on the ocean part of the image. Here is mine.

Compared to the original, it is a major improvement if I may so myself.

May your oceans be of the shade of blue you want.