color temperature

la temperature de couleur

The color temperature

This week I’m going to get back to the basics. It is true that in recent times I have responded to a number of you who want to read articles a little more driven, a little more geared towards the semi-pro see professional. In this article I will address a topic that I have not yet dealt with : the color temperature.

You are a lot to try to shoot short films with the means of the edge or more pro. Other form of video workshops , and, at each time, face to the color temperature. I warn you immediately, I’m not going to make it complicated, I am not an expert in light… we can’t be on top everywhere ;o) You’ll see why in the next paragraph.

Why do we speak of color temperature/ light ?

We talk about color temperature in a photo or during a shoot … just because the light outside, as a function of time and the time of day, does not have the same color. Ditto for the light that is inside of a house or a decoration function of the lamp that is used….The light of a sunrise is not the same as the light of 12h or 16h. Our eye makes automatically the correction because it is composed of cones that are present in the retina and that allows us to receive and decode the light.

Moreover, your servant is color blind (in the shades ;o)). I do not see the same colors as you because some of my cones are defective. All that to say that, if our eye makes the correction automatically and instantly, the camera that you use is not being made. Some cameras have what is called the white balance automatically, but sometimes this is not the top. Therefore, it is preferable to do it manually. But we’ll get to it a little later ;o)

If you are able to read the answer…not me ! ;o)

The color temperature is expressed in Kelvin.

In what way ?

I have long asked the question : why do we speak of temperature ? And why Kelvin ? I have a well written Kelvin and not Kevin…(If you call Kevin don’t be disappointed ;o)). A few years ago I found the answer…finally found is a big word lol. I asked the question to a chief op…I do not hide you that I felt a bit silly on the blow…and then at the bottom…it is shit ;o) I tell you this because there was a technician next to who looked at me with an air of say : ” You don’t know it ?!!! “

Ben non ! And in the end it either lol. It is for this reason that you should never think that your question is stupid or that you are going to spend for a nozzle.

So why is Kelvin (k) ? It is important to know that the kelvin to the same value as the degree Celsius. It may seem incredible and yet it is true except that the kelvin unit of absolute zero is -273 degrees Celsius. This is Lord Kelvin has studied the subject and who has found how to measure the color of a light. Like any person who finds a thing, he has just given its name to his find…and well not because the real name of Lord Kelvin is, in fact, William Thomson ! Humility when you hold us…or so Thomson was already taken….I assure you, it has given its name to a principle of thermodynamics ;o)

In short, Mr. Thomson was amused to heat a black object…

I do a little aside. Why a black object ? Simply because dark objects do not emit heat because they absorb the light while white objects, red or green to absorb part of the light , and return what may not be absorbed. What is “rejected” it is the color that we see….It might even be fun to philosophize about the true color of things…but we do have other cats to whip ;o)

So Will (It is a Lord but I call him by his pet name) has put it in an oven. By heating, the black object began to change color under the effect of heat. It has been compared to different sources of light that illuminated a white surface. When the object in the oven took the same color as the light source is reflecting on the white surface, it has raised the temperature of the oven and has added -273 degrees Celsius.

 

Let’s say I light up a sheet with a match. The flame of the match will give a color which will be reflected on the white surface. My object must be heated to 1427 degrees Celsius to have the same color as the light that returns the sheet. At this temperature, we add 273 degrees to have a color temperature of 1700 k which is the temperature of the light of a match.

Here is a table that will summarize the different temperatures as a function of the light bulbs or the sun.

The white balance

All that to say that you should absolutely do a white balance when you turn to be certain that your camera will capture the true ambient color.

I’ll tell you a story that has happened to me in my early days…I remind you that I’m color blind for shades and mixtures of colors. I distinguish bright colors but as soon as there are too many I’m lost, in short…a few years ago, I never would have told that lol

When one starts, we are ready to take everything that goes to make up the hand, to learn and to be a low paid etc… And by pure chance, I landed a job as cameraman for a corporate institutional which had obtained a contract for an evening of great company.

Obviously I am annoying, I know the camera by heart… I start to film the seminar, which takes place during the day, I do my white balance each time I change of place, in short, everything rolls. Comes the evening, here full of light and put it in the road…I know that I will not be able to do a white balance correct. So I decide to find a corner or the spots do not pollute the light base. I found a white wall and I do my balance. The evening is going well and I plan crazy. The next day, I mount, I dérush. And there is the drama ! All images of the evening are green ! The wall that I saw white…was not, the fact of being color blind, I had played a dirty trick ! Lol I can tell you how I stressed out ! I still managed to catch the blow, and deliver the film. They were so pleased that they have hired to do the light and to frame the film for the SNCF…and then I refused ! ;o)

All this to say that the white balance is of utmost importance ! It allows your camera to calibrate and correct the color cast, depending on the lighting, be it natural or artificial. In my story, I had the luck to have several moments well separated from each other. The evening that I shot was a special moment. That is to say that it wasn’t fitting in with a scene like this can happen in a movie.

It is thus necessary to make the white balance once your light is installed or that it is the light in which you are going to turn…and not be color blind lol

On your camera or in the menu of your camera you have an option for “white balance” or ” white balance “. For the do it you just need to take a blank sheet of paper or use a white surface to make this balance. You zoom in on the surface to fill your frame and then you press the button corresponding to the white balance.

I know that today the auto white balance works rather not bad. But I’m one of those who prefer to do it manually. By using the automatic I got caught several times when photos of tracking or the color was not good…that is why I continue to do it manually.

Moreover, if you have a camera you may have noticed the pictograms following :

 

And these pictographs are, in fact, scales of white preset depending on the place where you want to take the shot or video. If your device does not have the ability to do a white balance to manual (or if you’re really color blind) I advise you to use these presets ;o)

That’s it for this article on the color temperature. I hope this has enlightened (AHAHA joke naze mandatory) on the opportunities that you have. If you have any questions please do not hesitate to post them at the bottom of this article. I am sure that many of you will know what is the color temperature or white balance…but a little reminder doesn’t hurt ;o)

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Soon,

Tom Weil

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