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Blown highlights, they are the bane of the photographer’s life. Once you have blown your highlights in the original exposure, it will be virtually impossible to recover them in post production. Fortunately, we can avoid these situations by taking care with our exposure when we shoot and our cameras have some very good tools to help us with that. Let's take a look at how.
What is a Blown Highlight?
For the uninitiated, blown highlights occur when the amount of light in the scene is too much for the sensor to cope with. Your overall image might look well exposed but, for example, the sky might be a bright overcast and be completely overexposed, going completely white. When you take that image into Photoshop or Lightroom and try to recover that white area, it just ends up looking like a uniform grey patch with no definition.
How to Avoid Blown Highlights
Learn to Use the Histogram: You might have seen it on your camera but maybe you don’t understand its significance. That graph that you can display on your LCD screen is one of the most powerful tools your camera has. In the simplest terms the graph shows the distribution of light in your exposure, the darkest areas to the left and the brightest to the right. Anything falling on the right side of the graph is light and potentially becomes a blown highlight. When shooting in difficult conditions check the histogram after taking the shot. If your graphs spills out of the right side, then increase your shutter speed or close down your aperture until that graphs comes back inside. Check this article on how to use a histogram for better shots.
Highlight Alert: To some, it's an annoying blinking signal when they preview their pictures. To others it's a useful indicator of areas of blown highlights. The fact is the Highlight Alert is a very useful tool that will show you any area of your image that is over exposed and beyond recovery. To see either the histogram or highlight alert you need to switch these on from you camera’s menu system. Usually this is found in the image display menu accessed by pressing the menu button whilst viewing a photo. To check exactly how to do this, check you camera’s manual.
Use Filters: Another way to combat blown highlights particularly in skies is to use neutral density graduated filters. Available in 1, 2 or 3 stops, these filters go from dark to clear. Depending on how blown your highlights are. Placing an ND graduated filter will reduce the exposure in the very bright areas whilst maintaining correct exposure over the rest of the image. Square filter systems are the best option for graduated filters as you can carefully control the position of the graduation over the image.
Shoot Raw: Whist jpeg files might be fine for many things, when working in difficult lighting or when needing the best quality, nothing beats the power of a raw file. The reason for this is simple; you are getting the maximum dynamic range from your sensor. A shot that may appear to have blown highlights as a jpeg, may well be recoverable if it had been shot as a raw file. There are limitations of course but if you combine shooting raw with monitoring your histogram, you will soon learn just how far you can push the exposure abilities of your camera.
Understand Exposure: All these tools and techniques are great but to truly understand how to prevent blown highlights you need to understand the limitations of your camera. Every manufacture and model is different. Learn not only to understand the dynamic range that you camera is capable of capturing but also to read the light visually before you even lift the camera to your eye. Look at the scene in front of you, how dark will those shadows be? Can I get a decent exposure despite that bright, uniformly lit overcast sky. Look at the tonal range between the darkest and lightest areas and think about the technique your wish to use to capture it.
Blown highlights can ruin the most beautiful shot, yet but understanding how to control them and bring them back inside your camera’s abilities using one, some or all of the techniques above, you should be able to banish them for good.