- What is White Balance?
- White balance and CCT (Temp adjustment)?
- White balance and DUV (Tint Adjustment)?
What is White Balance?
If you ever found that the model or objects in your footage are yellow’ish or blue’ish? If you ever found that the skin of the model in your footage is green’ish? For digital film and video making today, we all know that it is due to the inappropriate lighting lamps and white balance management. For sure, you are able to get rid of these issues by post-production editing, while we also understand post-production editing will cost a lot of time as well as money. Therefore, to understand what is good lighting products and what impacts the white balance means a lot for the film, video as well as DSLR production.
The definition of White Balance.
In short, White Balance in film and video production is to correct the color casting in order to get natural and beautiful scenes. Through adjust the tint, filmmakers are able to eliminate the phenomenon of color shift therefore to create the footage as same as our human eyes’ view.
So, why filmmaking needs white balance?
Have you ever realized that, when we looking at the environment around us, our eyes and brain will automatically help us to judge the colors correctly although the white light source is changing and not pure. We are able to distinguish the white car on the road, no matter it is a cloudy day or a dimly orange’ish street light. Our vision system will help us to eliminate the color shift problem and give you the right sense to distinguish the correct colors. The brain will automatically adjust the tint difference in order to tell yourself it is a white car.
However, unlike our vision system, the camera does not have this dramatically intelligent system to deal with the colors captured from the lens. It can only deal with the colors based on the hardware of cameras and your experiential setting. If the light emitted from the lamps does not meet cameras’ hardware judgment, colors of the footage will be different from human eyes’ view. Inappropriate light from bad quality lamps would bring out blue’ish, yellow’ish, green’ish or magenta’ish problems of your footage. The colors of models or objects will be unnatural.
So, what influence the cameras’ or footages’ white balance performance? Let’s talk about it from two aspects: CCT (Temp) and DUV (Tint).
White balance and CCT (Temp adjustment)
What is CCT? Color Temperature?
CCT (Correlated Color Temperature). The color temperature is a typical way to quantifying different lighting condition in the scene. It means that the visual sense of how warm or how cold of light by numeral parameter, named Kelvin (K).
However, not all filmmakers or gaffers are familiar with the usage of color temperature. Instead, they prefer to use some typical name in the production industry for a better understanding of lighting conditions. The chart below listed some typical light sources and their corresponding color temperatures as reference.
|Color Temperature||Light Source|
|2500-3500 K||Tungsten Bulb (household variety)|
|3000-4000 K||Sunrise/Sunset (clear sky)|
|4000-5000 K||Fluorescent Lamps|
|5000-5500 K||Electronic Flash|
|5000-6500 K||Daylight with Clear Sky (sun overhead)|
|6500-8000 K||Moderately Overcast Sky|
|9000-10000 K||Shade or Heavily Overcast Sky|
What is the relationship between white balance and color temperature?
What if we have set the white balance of the camera, so, towards this setting, we need to use the correct color temperature lighting. If the color temperature is higher than camera needs, the footage will appear more cooler. On the contrary, if the color temperature is lower, the footage will be more like warmer. Therefore, if we want to get a neutral sense similar to human eyes’ view, the color temperature tolerance of lamps have to be small.
For example, if we choose daylight (5600K) cheap light with bad color temperature consistency, and if the color temperature tolerance of it is ±500K, as a result, the true color temperature in practice could probably be about 5100K or 6100K instead of 5600K true daylight color temperature. If we set and adjust the white balance of the camera with 5600K daylight, the footage would be yellow’ish or blue’ish.
White balance and DUV (Tint Adjustment)
As we all know, what the light we need for film and video production is pure white light. While apart from some general lights, most artificial light sources such as tungsten, fluorescent as well as LED lights are not able to strictly guarantee the pure white light. These types of lights probably will emit lights with tint shift. Or theoretically, we called it DUV, which is the parameter to judge the extent of tint shift of lamps.
What is DUV?
Duv is the short name of “Delta u,v”, which is defined in ANSI C78.377. As we mentioned before, every lamp has its unique CIE 1931 xy coordinate. And it describes the distance from the Black Body Locus (BBL) vertically. For film and video production lighting, it describes the extent of green’ish and magenta’ish.
DUV and Tint.
What we need is pure white light, however, not all film and video lamps made equally to meet the needs. Duv is a very important measurement to describe how pure the white light is and to describe the color shift towards green or magenta. Besides, because it is not enough to judge a light is good or not for film and video production only by color temperature (CCT), therefore, Duv becomes important as it provides vertical dimension from green to magenta to judge the lamps’ quality.
As for filmmakers or gaffers, DUV also is an unfamiliar criteria to accept. Instead, the green tint shift and magenta tint shift is more likely acceptable for them. While they are the same.
As we all know, other than the color temperature, there is another parameter we need to adjust for post-production white balance, which is TINT. If we make the movies or videos under natural sunlight, we do not have to adjust tint. If we make our art-work under some artificial lights and the light is not qualified, we have to adjust tint a lot. This is due to the Duv shift or tint shift, or green and magenta tint shift.
Duv has positive and negative values.
Assume the light emitted from your lamp is not pure white light, and the Duv value is a plus, it means the CIE 1931 xy coordinate of your lamp is above the black body curve. This lamp is a green’ish light source. The footage made under this lamp will be green’ish, especially the skin tone of actors.
If the Duv value is a minus, it means the CIE 1931 xy coordinate of your lamp is blow black body curve. This lamp is a magenta’ish light source. The footage made under this lamp will be magenta’ish or pink’ish.
Due to these two factors, CCT and DUV, once the quality of the film and video lamps is not good, it will bring about huge work difficulty for filmmakers and gaffers. Besides, if the lamps cannot provide good performance for white balance during the shooting process, the team have to deal with it by software in the post-production process and consequently increase the extra time and money cost for a film and video project.