What is Contrast Ratio, High Key and Low Key Lighting
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What is Contrast Ratio, High Key and Low Key Lighting

The simplest explanation of Contrast Ratio, High Key and Low Key Lighting.

First, watch the video:

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Lighting Contrast Ratio

Lighting contrast ratio is not really a ‘ratio’ in cinematography:

Lighting contrast ratio is the difference in stops between the bright (key) and dark (shadow) portions of a face.

Note: Photographers use contrast ratios that are 2:1, 3:1, etc. This is not used by cinematographers due to the way lighting is done traditionally. I’ve never found any good reason to use this system either, because it just complicates things for no real benefit.

If the key reads f/5.6 and the shadow side reads f/2.8, the difference is two stops (f/5.6 to f/4 is one stop, and f/4 to f/2.8 is a second stop). The contrast ratio is 2 stops. We say “two stops over” or “two stops under”, and mostly don’t even use the word ‘ratio’.

A stop is double the light, so the lit side is four times higher exposed than the shadow side.

Learning to communicate about lighting in stops is important.

If it’s only half a stop above, the contrast ratio is half a stop. For really moody and dark scenes the contrast ratio can be 4 stops or higher. Gordon Willis frequently used large contrast ratios in his lighting style. The typical average is about two stops, though it varies from scene to scene, depending on what the cinematographer is trying to achieve.

What is flat lighting?

If the key and the shadow are the same exposure, then we call it flat lighting.

There are two aspects to flat lighting. You can just light a face flatly, where the contrast. ratio on the face is the 0, or no difference. But in cinematography, when people use the word “flat lighting” they also might mean the lighting contrast of the scene as a whole.

Scene Contrast Ratio

The lighting contrast ratio on the face is only one half the story. The other contrast ratio is the difference between the lit side or key, and the background.

There really is no name for this. You could call it the the scene contrast ratio, though I don’t recommend it.

It is also measured in stops.

The most common technique used from the earliest days of cinema is to have the background one stop darker than the subject. 

High Key and Low Key Lighting

High key and low key lighting refers to the contrast of an entire scene, not just the face.

When a scene has a high contrast (great difference between the brightest and darkest portions of the face), we say the scene is low key. Lighting used to get this look is called low key lighting. Here’s an example:

citizenkane

On the other hand, when a scene has a low contrast (small difference between the brightest and darkest portions of the face), we say the scene is high key. Lighting used to get this look is called high key lighting. Here’s an example:

mary

Exception: A moody scene with low contrast is not usually called a high key scene in cinematography:

mirror
sailingboats

Not all terminology has a logical basis. Some have just evolved over the years. The same terms in photography might mean different things.

In cinematography, you typically find these terms used in the following way:

TermRefers toMeaning
Contrast RatioFaceDifference between brightest and darkest portions of the face, or between the face and the background.
High Key LightingSceneDifference between brightest and darkest portions of an entire scene is low, but the scene itself is bright and cheerful. Moody scenes aren’t counted.
Low Key LightingSceneDifference between brightest and darkest portions of an entire scene is high

How to remember high key and low key lighting setups

To understand high key and low key lighting, let’s take some common scenarios. You could either have:

  1. An overexposed foreground or background,
  2. an underexposed foreground or background, and
  3. a middle exposure, which is about 2 stops above or middle middle grey.

With these three possibilities, you get a total of nine combinations between foreground and background. You have:

  1. black-black,
  2. black-grey,
  3. black-white,
  4. white-black,
  5. white-grey,
  6. white-white,
  7. grey-black,
  8. grey-grey and
  9. grey-white.

Let’s say you have grey-black:

grey-black

This is called low key lighting in cinematography. I use the term in the way I’ve learned it from books and cinematographers interviewed in ASC magazines.

Going forward, what if the subject is overexposed?

white-black

Against a dark background, it’s always low key lighting. Black on black is also low key:

black-black

It’s very easy to remember low key lighting.

When the background is dark to the point of underexposure, or actually underexposed, or even black, it’s always low key lighting.

Low key lighting is used to create a sombre or sad mood. Watch this:

Now let’s go in the opposite direction. When the subject is correctly exposed or overexposed against a bright background, we have high-key lighting.

white-white
grey-white

High-key lighting is used in many sitcoms and comedies, because the world is always a cheerful place. It’s easy to remember because the background will be brightly lit and cheerful. No unnecessary shadows to spoil the mood. Cartoons are a great example of high key work.

If you have a white background or grey background, by which I mean about two stops above or below middle grey, but the foreground is underexposed or even black – it’s called a silhouette.

black-white
black-grey

There’s no ambiguity. All this is common knowledge on film sets.

If we have a grey background with either a grey or white foreground, it’s just normal lighting. This is what the majority of scenes look like:

grey-grey – typically what happens with darker skin tones.
white-grey – typically what happens with Caucasian skin tones.

The ‘middle’ grey range

If everything is in the realm of grey, the background is one stop below on average, which is below the two stops we need for grey.

Up to two stops is fine. More than that and the look gets moody and serious.

The fill side or shadow side will generally match the background. It’s rare to have a dark shadow side but nowhere in the room is it that dark. That will look unnatural.

So, there’s no need to look at the face for high key or low key lighting. You look at the background. That tells you everything you need to know.

This is specific to cinematography because in cinematography you are lighting spaces and scenes most of the time. All the shots taken in that scene and space have to match. Getting the mood right is critical.

Summary

  • Lighting contrast ratio is the difference in stops between the key and the shadow.
  • High key is when the background either matches the foreground in correct exposure, or if the background is overexposed.
  • Low key is when the background is underexposed or black, regardless of what the subject looks like.
  • The silhouette is a special case where the background is correctly exposed or overexposed, but the foreground is underexposed or black.
  • Everything else is normal lighting, by which I mean the kind that doesn’t contribute a lot to manipulating the mood.

That’s it. There are no other variations possible. Sometimes you fall into a grey area, but that doesn’t really matter because the cinematographer’s eye and experience will tell them what the mood is like.

After all, lighting is just one aspect of mood. Humans also use other cues like the actor’s wardrobe and expression, and the context of the scene, what’s happened before, etc.

The best example I can think of is The Shining, in the bathroom scene. It’s lit to high key, but the mood is anything but. And for the reverse study Manhattan, where the lighting is mostly low key, but the subject is comedy. You can break the rules as much as you want.

I hope this has helped you understand contrast ratio, high key and low key lighting.

6 replies on “What is Contrast Ratio, High Key and Low Key Lighting”

My question is how did the aperture of the lit side f/5.6 and whereas on the shadow side is f/2.8???? Means how did the light meter read a wide open aperture on a shadow side and a narrow aperture on the light side? Can you please answer this question to me????

I have an article and video on how to use a light meter. Check it out.

The light meter is set to give the aperture reading of middle grey. The aperture has to be more open on the dark side to get middle grey, and closed on the light side.

Just looking at my comments I ment to write your best. I hope you were not offended by my haste in writing. I’m very sorry if my comment was taken the wrong way.

Thanks for your response.

RG

Hello there, I watched your video and for the most part it is fine. The explanation of contrast is very good. I do believe you are mistaken on the calculation of contrast ratio.

Contrast ratio is calculated at 2^ of the stop difference between the key side and the fill side. For instance, if your key is at 5.6 and your fill is at 2.8. Then you have a difference of 2 stops.

Using the above formula your calculation should look like this: 2^2 = 2×2 =4 which means the contrast ratio is 4:1.

Please do your bs to correct thist. If I am mistaken please let me know.

I hope my post was helpful.

Respectfully

RG

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