By Eugene Struthers
What is the histogram? And should you use it?
The modern digital camera has the ability to evaluate an image and tell us if it was captured with a proper exposure. It does this by using a histogram, which is a graphical representation of the light levels within an image. Broken down into the tonal range of light levels and there colour intensity and the number of pixels per each level, intensity and colour spectrum.
Definition: “Glamour-photography definition” The histogram is a graphical representation of the tonal range, colour and light intensity of each pixel within your image. It indicates the true light levels and intensity as captured by the camera’s sensor.
The histogram gives an indication of our exposure levels for a particular lighting condition. And it serves as a guide for the photographer to obtain maximum exposure within the camera. The main reason why a new photographer should start to use the histogram is based purely on the easy at which they will be able to instantly get an overall indication of the lighting conditions present in their images. Put simply, if you are only looking at a preview of an image to gain an insight into whether or not the image is correctly exposed. You will be missed lead. And there are six main reasons why just looking at the image on the back of your digital camera could give you a false indication of your exposure levels and light intensity. These are:
The Image which you are previewing is that of a JPG. A JPG basically means that all the data- pixel information, the colour tonal range is compressed according to the presets of the digital camera internally. This compressed data can be miss-leading as it applies its own presets to the image for the photographer. JPG preview images are in most cases slightly off from the true lighting conditions captured by most photographers. Whilst a RAW image is uncompressed data and the photographer can apply his own presets (editing) to a large pool of data pixel information, tonal range and colour intensity. It allows for more flexibility and image manipulation. If you shoot in RAW, then always use the histogram. Digital camera manufacturers use JPG to save internal memory space when processing an image.
The ambient light may not be a true reflection of the lighting conditions you are seeing in the preview LCD of your digital camera. The LCD screen could be dimmed or too bright, so it can miss leading and cause the photographer to think they have the correct exposure. Whilst being under or overexposed in reality.
If shooting in one of the auto modes (Aperture priority, Shutter priority, Program mode) you have a specific picture style setting, preset into your camera which may influence the overall image character and visual lighting conditions within your image. Thus not giving a real and true indication of the actual lighting conditions. Or falsifying the existing data info readings.
You may have the wrong white balance set within your camera. This can throw true lighting exposure levels off, and give an incorrect reading.
In manual mode, you may just be exposing incorrectly, as a result of using the live view on the back of your camera's LCD screen and not the actual exposure indicator through the viewfinder to compose and obtain the correct exposure.
The LCD screen on the back of your camera is uncalibrated, so it isn't giving you a true indication of your light levels if you are only looking at an image on the LCD screen to verify if you have obtained the correct exposure.
The modern digital camera, 2017 and onwards, now have the ability to live preview the histogram whilst obtaining the correct exposure and composition. This saves a lot of time and eliminates the process of having to take a test shot, then preview the image on the LCD screen and then pull up the histogram to verify if the exposure is correct. Before, actually taking another shot once the correct exposure has been obtained. Using a histogram will save you time and take you to the next level in your photography. It will enhance the colour tones within your image and allow you to experiment and develop your own style. Basically, the histogram allows a photographer to see if there are any problems with their exposure. So why wouldn't you use it?
How do you read a histogram?
The modern digital camera is able to read the quality of light it receives by means of the built-in light meter within its sensor. The light that reaches the sensor is broken down according to the level and quality of its tonal range. And this mainly depends on the light conditions in which the photographer has taken an image in.
The sensor then groups these different qualities of individual specs of light according to their own specific tonal range. The individual specs of light are read by the internal sensors- pixels and grouped according to how many are present for each specific tonal range (light quality). The grouping and allocation of these different tonal range groups are what the histogram represents. So the greater the sensor the better its capabilities are of analysing different light strengths, qualities and tonal ranges.
The horizontal x-axis on the histogram represents the luminance - tonal range (quality of light). And the vertical y-axis represents the number of pixels per each individual tonal range. The right side represents the highlights or bright areas whilst the left side represents the blacks and shadows. The middle section is where the mid tones and 18% grey are represented. The height at which the peaks reach represents the number of pixels in a particular tonal range.
Each tonal range is broken down according to there own specific light quality from 0-255 (0 being black and 255 being white). After previewing an image and pulling up the histogram, we are then able to verify in which tonal range most of the pixels lie according to the lighting condition the images were captured in. The histogram (digital light meter) will indicate whether an image is overexposed, underexposed or has been taken at the correct exposure. It gives an accurate indication of the quality of light reaching the sensor. And it guides the photographer on how much light is required by the sensor to obtain perfect exposure.
The histogram is covered in more detail here: Click here The digital photography course (2019)