Lights, black bodies, diving color temperatures
Light sources, black bodies, color temperatures of pictures and underwater movies
Color rendering in underwater photography
On photography and underwater video, the rendering Colors of fishes or marine landscapes creates many problems to the photographers.
In a previous article about the color of the sea, we have seen that different wavelengths of visible sunlight are rather quickly absorbed by water.
Although in some day conditions, we can use color filters to balance pictures or Videos . But, most of the time, it will be necessary to have a more or less powerful source of artificial light for make good shooting. This is where the trouble begins. Indeed, each light source is characterized by what is called the color temperature . Control of artificial light is a delicate but really essential thing.
Color temperatures and black bodies
The color temperature characterizes the light from a light source, compared to an ideal material, called black body , which emits light only when it is hot heated. Well, here we are good, but what exactly is a black body?
Theoretically, a black body is an object that absorbs all the electromagnetic energy received, without thought or transmit any. Light is electromagnetic radiation. So, a black body appears to us black because it absorbs all colors of the visible spectrum. However, it may emit light when heated to a sufficiently high temperature, between 2000 and 12000 ° K. This light emission has a particular color directly related to the temperature of the black body. This is measured in Kelvin degrees as the color temperature of a light source. Kelvin is an international system unit which is easily convertible into Celsius degrees. 0 °C = 273 °K.
Let’s take an example to understand better. If we have a lamp with a color temperature of 3500 K, it will emit light with a yellow cast as a black body heated to the same temperature of 3500 °K , in other words 3227 °C. Well, okay, but curiously, when we dive with a beautiful White color light, we do not feel that the light is yellow. Then, if we take pictures they show more or less this unpleasant dominant color. What is happening then?
Here is an example of different tones on picture. To the left uncorrected, to the right with correcting the dominant yellow.
In fact brain is capable of many wonders. Thus, when the light fades, it corrects the light seen by our eyes to make it as light as possible and as close as possible to daylight. Some cameras are scheduled to try to do the same job by automatically playing White Balance , we will come back later in a future article. Many do not have this feature yet, colors are recorded without qualms by the camera. Nothing serious, image processing software know exactly balance the colors. Unfortunately for purists, image treatments may have a partially destructive quality of the original pictures. So there will be a great interest in equipping with lamps or headlights which the color temperature closed to daylight.
The choice of light source, LED or others.
Many choice is offered to the photographer candidate. Personally, since I often dive at night, I opted for a light-based LED « Daylight ». This lamps produce a very white light, unfortunately quickly absorbed by the particles if we do not work in macro. They serve to enlighten me during the ride as well as to provide me with a very easily directive light on pictures and movies. LEDs providing cold light produce a blue light color that I personally do not like. Those providing Hot light produce too yellow tone, and sometimes curiously to green or pink tones.
I can not discuss here the interest of flashes or HID lamps because I never use them. I let the opportunity to those who would talk about it to do through the forum or to offer me a text to include in a future article.
whatever the artificial lighting mode, there will always consider the turbidity water. More will be charged more the color recorded by the camera will move away from the feeling through the mask. The flashes have a very good color rendering and are powerful, but in troubled waters it becomes more a handicap than an advantage. Particles may be overexposed and cloud the picture.On the other hand, the flash is not very suitable for macro picture because of overexposure problems of some highlights. Obviously, for video, lashes are useless. I do not know what you are thinking about, but me, I love video. I will also discuss about it in a next article.
Meanwhile, good diving to everyone, enjoy your dive the water heats up.