Perhaps you’ve heard the term histogram but were too scared to ask what it meant? Luckily I’m here to tell you more and help you use it effectively. This little tool can help you take control of the way you expose your pictures.
Let’s have a look at the basics first….
What Is a Histogram & How to Read One?
At its simplest, a histogram is a graph. Your camera sensor capture light of all intensities, on a scale from 1 (the blackest black) to 255 (absolute white). The histogram shows the distribution of these intensities, depicting how many pixels have been captured at each level of brightness.
The darkest shades are shown on the left-hand edge of the graph and they gradually become lighter until you reach absolute white at the far right-hand edge.
Most images will contain a spread of tones, showing as a range of peaks and troughs across the histogram. However, in some pictures, the spread will be more limited. Let’s take a look at some examples to illustrate this.
There Is No Right or Wrong Histogram
It might seem an admirable ambition to always have a histogram like the one above, but in reality, it’s just not a one size fits all thing!
Let’s take a look at some examples where the histogram isn’t ‘perfect’, but instead reflects the type of image the photographer envisaged.
Shadow Clipping (Under Exposed, Pure black Areas)
Shadow Clipping is when a photo includes pixels which hug the left side of the histogram. This means the image includes areas of pure black, which contain no detail.
For instance, below we have a very dark picture. There are a few lighter tones, but it’s mostly about the shadows. When I shot this I knew I wanted a dark photo to create that feeling of mystery and drama. So I purposely underexposed the scene to create the look I wanted. In the histogram, the graph touches the left-hand edge, showing there are some pure black tones. I don’t mind this as we don’t need to see any detail in these areas.
Highlights Clipping (Over Exposed, Pure White Areas)
Highlights Clipping is when a photo includes pixels which hug the right side of the histogram. This means the image includes areas of pure white, which contain no detail.
Looking at the opposite extreme, this Red Kite flying against a bright sky contains no complete blacks at all. The overall brightness of the image means the histogram is mostly over to the right. However, I judged my exposure so that the brightest tones got close to the edge of the histogram, but not touching it. This way highlights are not completely blown out.
Pro tip: most cameras have a feature called “Highlight Alert’. When enabled, it will blink the overexposed highlights in playback mode. This is a warning to let you know that details on those areas are lost. Look at your camera’s playback menu settings
Sometimes Pictures Have a Little of Everything!
Of course, there will be some situations where you shoot a photo containing both extremes of the exposure spectrum. In this sunrise photo, there are very dark shadows, as well as bright highlights.
When I shot this, the sun was a little overexposed. However, because I shoot in RAW format, I was able to rescue it in post-processing and bring the brightest tones down, just inside the right-hand edge of the histogram. This is a situation where shooting in RAW is an advantage as it gives you a little more latitude.
Why Should I Use the Histogram?
Using the camera’s histogram allows you to check whether your photo contains a good spread of tones and, more importantly, whether you’ve blown out any of the highlight or shadow tones.
If you try to photograph something that is brighter or darker than your camera is actually capable of ‘seeing’, the sensor will simply register those tones as pure white or pure black, containing no detail.
If you have any overblown shadows or highlights, you can then adjust your exposure settings and shoot again. You do this by using exposure compensation (in aperture priority mode or shutter priority mode) or by changing the aperture or shutter speed in manual mode.
Put simply, understanding the histogram puts you in charge of exposure, not the camera!
Why Not Just Fix Exposure in Post Processing?
If you’re shooting an unrepeatable moment and get the exposure wrong, you may have to do just that. However, it’s always better to try and get things right in camera.
Best practice is to always capture as much detail in camera as possible.
An overexposed image will have highlight areas which are pure white and contain no data at all. Once this has happened, no amount of Photoshop work will be able to bring back those highlights.
If you have an underexposed image and try to heavily boost the shadows in post-processing you should expect a nasty, noisy mess. Admittedly, it is generally easier to retrieve detail from shadow areas compare to highlights, but the end result is rarely pretty.
Far better to get it right in camera.
How to Handle Tricky Lighting Situations in Photography
If you find you’re shooting a scene which includes bright highlights and deep shadows, you have several options to avoid blown out shadows/highlights.
- Create an HDR image. Shoot several different exposures and combine them in Lightroom or Photoshop to create an HDR (High Dynamic Range) image which contains data of all tones.
- Use an ND Grad filter. These are special types of filters that gradually darken half the filter. You can place the highlights (such as the Sun) over the dark areas of the filter so that highlight details are not lost.
- Expose to the right. Choose an exposure which brings your histogram as close to the right hand side as possible, while not actually crossing the line. This gives you the maximum amount of data to play with in the brightest tones (you have a better chance of recovering shadows in post-processing later)
How to Enable Histogram
On most cameras, you can click on the info button while you are in image playback mode to display the image histogram.
You may have to click it several times since this button is programmed to display other info as well.
RGB Vs. Luminosity Histogram
Many cameras offer a choice of a simple luminosity histogram (grey ) or an RGB (color) histogram. But which one is best?
Digital cameras record our images using a combination of red, green and blue pixels. If you choose the simple histogram (which is generally the default choice) it simply shows you an average of the three color channels. This seems logical, but can be misleading.
Imagine you’re photographing a field of red poppies. Which color channel will have the most data? Yes, that’s right – the red one! The simple histogram, by showing you an average reading, will almost certainly not give a true picture of the red tones in the image. Red is a particularly sensitive channel and is the most likely to overexpose. Therefore, a better choice is to select the RGB histogram, which shows the three channels separately. With this enhanced information, you can immediately see if your red poppies are overexposed and take action to correct that.
Again, the settings for the RGB histogram option will be in the playback or display options. Most modern cameras offer this option so it’s worth consulting your user manual if you can’t find it.
After you’ve enabled the histogram on your camera all you need to do is go and shoot some photos.
The critical areas are those at either side of the histogram. A peak of pixels hard against the left or right edge of the histogram shows you have pure black or pure white pixels in your image, which can’t be rescued.
To remedy this, simply adjust your settings to either brighten or darken your exposure and shoot again. A good exercise is to shoot several identical frames at different exposures and see what difference this makes to the histogram. This way you can clearly see cause and effect.
Example 1: Overexposed (clipped highlights)
Example 2: Underexposed (clipped shadows)
Example 3: Properly exposed (no details lost)
When Should I Use Histogram?
As often as you want!
If you’re shooting in an environment with even lighting and no great contrasts of tone, checking your histogram for every shot is overkill. But, if you’re taking photos in contrasty conditions, with extremes of light and dark, I would recommend checking it out regularly.
It’s worth pointing out that there will always be some unavoidable sources of overexposure. The sun, for instance, is the brightest object in our galaxy. It’s important to remember that the sun will almost always be overexposed if it’s directly visible in a photo. It is sometimes possible to reduce the exposure when shooting to avoid this (particularly if the sun is very small in the frame) but this may also result in shadow areas which are heavily underexposed. Every human being knows the sun is very bright so you may feel it doesn’t matter if it burns out a little.
Another source of overexposure in your histogram can be specular highlights. These are the small flashes of bright light which occur on shiny surfaces. Think of sun reflected off dappled water, or highly polished chrome accessories on a classic car. If these appear in your photo, they will register on the right-hand side of the histogram. Do they matter enough to compromise the entire exposure to correct them? Probably not!
Now it’s your turn…
Now I’ve helped you understand histograms better, why don’t you take that new knowledge out for a spin?
I’d love to see some of the resulting photos in the comments below. Why not share an image or two where the histogram has particularly helped you? I’m looking forward to seeing your pictures!
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