Basics of Photography:
High Key and Low Key
Photography
Do the words high key and low key photography intrigue you? Have you tried creating such images and faced problems? Don’t worry! This article will introduce to you the basic concepts of high key and low key photography. It will also explain to you how to create the needed effects with suitable lighting; but first, let us see what these terms mean. A photograph with predominantly light tones is termed as a “High Key” photograph. Such an image will have light or no shadows (or dark areas). High key photographs are generally associated with a “happy” mood and are extensively used in fashion and product photography. The overall contrast of the image is low. The main colour here is white. On the contrary, photographs that have large areas of dark tones are called “Low Key” photographs. These pictures have few or no highlights. They are associated more with a somber mood. Low Key images are created with either side or back lighting. The latter creates the rim light which accentuates ( highlights) the contours of the subject body. The overall contrast of the image can be very high. The predominant colour here is black. Both high key and low key photographs generally tend to be monochromatic. The lighting technique that is needed to create a high key photograph, as you would have guessed, is called high key lighting. Likewise, you have low key lighting for creating low key photographs. Techniques for creating high key and low key photographs, challenges that you might encounter while creating them and solutions to those problems is the subject of this article. To understand all that, you need to revisit the basics of exposure. So, here we go! An exposure meter that is built into your camera measures reflected light. However, it has no idea whether the light it is receiving (to measure) was reflected from a light toned subject ( like snow) or from a dark toned subject ( like coal) though the former reflects a lot more light than the latter. Here is an analogy that will make the concept clear. Can you tell how far the source of a sound is, just by the volume ( loudness) of the sound? You cannot, because a very loud sound a mile away will sound less intense compared to the sound from your stereo just a few feet away. Similarly, just by measuring the intensity of the reflected light, a meter cannot tell if it has been reflected from a light toned subject or a dark toned subject or anything in between, although the reflectance would be different in each case. So, what does your camera meter assume the tone of the reflecting subject to be? The meter always assumes that the light is being reflected from a medium
toned subject and hence converts the subject to a medium tone. Note that the medium tone is the tone to which all photographic meters are calibrated as per internationally accepted standards. Look at this in some more depth. What happens is that a meter will treat a high key scene as a medium toned scene in more light. Hence, it will give less exposure than what is needed,
rendering the scene darker due to underexposure. The converse happens with a low key scene. Instead of looking at it as a low key scene the meter will treat it as a medium toned scene (as always) in less light. Hence, it will give more exposure than what is needed, rendering the scene lighter due to overexposure. The consequence is that both scenes will be rendered (recorded) as medium toned, which is the calibrated tone of the meter! We can summarise by saying that all photographic meters are “tone blind” as they do not take into account the reflectance of the subject. Hence, you need to remember that if you meter a scene that is not medium tone, as is the case with high and low key scenes, then you need to change the exposure as given by your camera’s exposure meter. This is done by giving suitable exposure compensation. If you are photographing a high key subject, then you need to allow more exposure, that is, you should give positive exposure compensation ( Pictures 1 and 2). This will increase the exposure from the camera reading that would have caused a medium toned image capture, to something lighter. You need to do the opposite - that is, give negative compensation for a low key subject so that it comes out dark and not medium toned ( Pictures 3 and 4).
In other words,
The actual tone of subject does not matter! The meter reading will be such that the area you measure will be rendered medium tone in the image.
It is you who has to decide how you want the subject to be rendered - medium, dark, or black, or light, or white, or anything in between. You will need to give compensation accordingly, using the Tonal Variation table featured here.
How to set compensation:
You can set exposure compensation in two ways. If you are using an automatic exposure mode ( like aperture priority, shutter priority, etc.), you can use the exposure compensation button and dial in the needed compensation. However, for critical work, automatic exposure modes (especially when used along with a spot meter) are not very convenient. Just use the manual exposure mode and you can set the exposure compensation by observing the appropriate marker on the exposure scale in the viewfinder. There is no need to use the exposure compensation feature on your camera at all. Once you select the manual exposure mode, an exposure scale ( looks like a ruler used by students) appears in the viewfinder ( Picture 5). However, instead of being marked in centimeters and inches it is marked in exposure stops ( hope you have not forgotten what a stop means). The underexposure is to the left and the overexposure is towards the right. To the left and right are stops which are marked in ½ stop (0.5 EV) intervals. The scale here shows a range of - 2.5 to +2.5 stops. If the symbol > is illuminated, it indicates that the overexposure is beyond 2.5 stops. Likewise, if < is illuminated, it indicates that underexposure is beyond 2.5 stops. The central marker is illuminated when the exposure is technically “correct” ( Picture 6). That is, if you take a picture as it is at this exposure ( without changing ISO or shutter speed or aperture), the area over which you had measured will be rendered in medium tone. If any other marker is illuminated ( Pictures 7 and 8) the said area will be rendered lighter or darker by an amount as indicated by the illuminated marker. This is merely a visual indication of the exposure compensation. Note that in some cameras, (example Nikon cameras) these directions are interchanged, that is overexposure is to the left and underexposure is to the right. Also, the exposure scale in some cameras is marked in 1/3 stop intervals rather than 0.5 ( half stops). Please note and set the compensation accordingly.
How the exposure scale works.
Those of you with a keen eye might have observed that this is just a graphical representation of the Tonal Variation Table. Your D-SLR will also offer several metering modes viz., evaluative (also called matrix), center weighted and spot. Evaluative meters take certain decisions after they measure the light resulting in an exposure that may not always be predictable. The center
weighted meter also measures a large area that may have more than one tone in it. Hence, for critical work it is best to use the spot meter ( Picture 9) of your camera. The area measured by the spot meter is marked by a small square in the camera’s viewfinder. Most modern D-SLRs have a number of spot meters, each corresponding to one AF point ( Picture 10). The measured area can be set at any tone by giving compensation as described in the Tonal Variation table. It is important that you remember that this is so regardless of the original tone the subject! For more details on how to set your camera to manual exposure mode and spot metering, refer to Smart
Photography, ‘ BasicsofPhotographyExposureControlsinD-SLRs’ ( May 2012). In high key or low key photographs the tones of the subject and the background tend to be close to each other. They can possibly be in the same colour too. So, there is a tendency for the subject to merge with the background. However, what you want is a good separation between the subject and the background to properly demarcate the former against the latter. To achieve this you need to choose the tones of the subject and background suitably and light them carefully. Interestingly, the human eye is influenced more by the tone of the background. So, for a high key photograph you should preferably choose a very light (or even a pure white) background and a slightly darker than the background ( but still very light) subject. For a low key photograph you should choose a very dark (or even a pure black) background and a slightly lighter ( but still very dark) subject. To achieve proper demarcation you need to have approximately a half stop exposure difference between the background and the subject. Thus, in a high key photograph the background must be around ½ stop lighter than the subject and in a low key photograph, the background must be around ½ stop darker.
How to set exposure accurately:
Every scene has a brightness range that is, the tonal variation between the brightest and darkest part of the scene. This is measured in stops. Generally a sensor can be expected to have a 5 stop range though more expensive cameras have a larger range (around 8 stops). This means that the camera can record in the same frame two objects - bright and dark with proper detail provided the difference in their brightness is not more than 5 stops that is, plus or minus 2½ stops on either side of medium tone (see the Tonal Variation Table for more details). This is called the dynamic
range of the camera. Remember that when you are capturing either high key or low photographs, you are working at the near limits ( boundaries) of the dynamic range and hence exposure has to be very precise. If the exposure you set exceeds the dynamic range of the camera, then the result will be blown out highlights or blocked shadows. The former is likely to occur when you are photographing high key images as the positive exposure compensation you set can take the highlights beyond what the camera can record. This will result in blown out, detail-less highlights from which you cannot recover any detail, even with post-processing. The reverse can occur when you are photographing low key scenes. Here, the negative exposure compensation you have given can take the shadows beyond what the camera can record. The result is blocked detail-less black patches. Both blown highlights and blocked shadows look ugly (unless of course you are using them for a purpose) and should be avoided.
Fortunately, your D-SLR has built-in tools that can help you avoid these issues. To start with, do not rely on the played back image seen on the LCD monitor of the camera to check these problems. Switch on the highlight warning and histogram tools and check for any overexposed and underexposed areas. These are in the playback menu. The highlight warning tool when switched on will indicate the blown out areas with “blinkies”. That is, those areas that have blown out will blink alternatively black and white. You have to reduce exposure if you want to reduce or eliminate them. One advantage of the highlight tool over histogram is that, it indicates to you exactly the areas of the image that have blown out. The histogram tool shows you how the tones are distributed in an image. The right side of histogram denotes lighter tones and left side darker tones with mid-tones in the middle. The right axis shows pure detail-less white and left axis pure detail-less black. The height of histogram at any point shows the number of pixels at that particular tone. Thus, a very high peak at a particular tone indicates that there are a lot of pixels with that tone. This also means that a larger area of the image is at that tone. As you would expect, a histogram of a high key scene will be bunched towards the right ( Picture 11) as it will have predominantly light tones. However, if the histogram touches the right axis it means that some areas of the captured image have blown out. These will correspond to the blinkies visible with the highlight warning tool. If that is the case you may have to decrease exposure if you want to reduce or eliminate them. A histogram from a low key scene will be bunched towards the left ( Picture 12) as it will have predominantly dark tones. If the histogram touches the left axis, it means that some areas of the captured image have blocked shadows. ( Unfortunately, there is no tool like the highlight warning tool to indicate where the blocked shadows have occurred). If this happens, you may have to increase the exposure to bring out some details in the shadows. While a blown highlight is devoid of all detail, you can get some details out of an underexposed area through post-processing. However, those areas will have a lot of noise after post-processing and hence you should do this only as a last resort. As always, try and get the exposure right first time rather than try to salvage an image due to bad exposure later through postprocessing.