My focus this year will be on Proper Exposure: what it is and how to achieve it. Have you ever wondered why some photos seem to “pop” and grab your attention while others don’t? There can be many reasons why, but often it’s a matter of proper exposure. Proper exposure maximizes contrast and the human eye is drawn to contrast.
Each of the following images has a problem with the exposure. The first image is underexposed, i.e. there aren’t any light pixels. The second image is overexposed, i.e. there aren’t any dark pixels. The third image isn’t too light or too dark, but it looks flat because the darkest parts are just dark gray (not black) and the lightest parts are light gray (not white) resulting in an image that looks somewhat lifeless. This can sometimes happen in shade or cloudy skies.
In general, a properly exposed image means that lightness values run the full gamut from black to white (instead of dark gray to light gray). There are always exceptions to the rule, but this is very often the case.
But how do we know for sure when we have the proper exposure? Simply relying on how the photo looks on your camera LCD or phone does not always give you a true representation of the photo. Luckily there is a tool called the Histogram that gives you the information you need at a glance.
What is a histogram? It’s simply a bar chart. As an example, imagine that we want to create a tile mosaic of a sunflower. Because we’re focusing on exposure (i.e. luminosity or lightness values) let’s make the image B&W so that it’s easier to “see” the luminosity values. To further simplify things, let’s reduce the number of lightness values to 10. If we were to count the number of tiles of each value and display those counts in a bar chart, it would look like the chart below:
This is the essence of a histogram: a bar chart which shows the number of pixels in a photo of a particular luminosity value (which runs along the bottom of the chart). The difference is that the histogram of a photo has 256 luminosity values – 0 (black) to 255 (white) – instead of just 10. However if you compare the histogram of the photo with the simple bar chart from the mosaic image, you can see that the basic distribution is the same.
It’s important to realize that there is no ideal shape for a histogram, i.e. you are not trying to get a “bell curve”! The histogram is a tool to help you understand how well exposed a photo is. Looking at the histograms of the three images we started with, you start to see what a histogram can tell you. When the histogram is weighted heavily to the left, the photo is typically underexposed. When it is weighted heavily to the right, the photo is typically overexposed. When it doesn’t stretch across the entire luminosity scale (from 0 to 255), the photo lacks contrast and appears flat.
While there is no ideal shape for a histogram, in general the most eye-catching photos have a histogram that covers the entire luminosity scale from 0 (black) to 255 (white). Note that the histogram for the good exposure is more spread out than the low contrast one. The left (dark) and right (light) sides of the histogram are more filled out which indicates that the dark areas of the image have gotten darker and the light areas have gotten lighter, thus increasing the contrast.
There are two exposure issues that cannot be corrected in post-processing: clipped (aka blown-out) shadows and highlights. “Clipped” essentially means that there is no detail in the very darkest or very lightest parts of your image. Referring to the histogram when you review photos on your camera can help you avoid both situations! If a histogram has a tall spike pushed up against the right edge, your photo has blown-out highlights that you will not be able to recover in post-processing. I’m sure you have seen this in landscape photos where clouds look like white blobs in the sky without any texture in them. Alternatively, if a histogram has a tall spike pushed up against the left edge, your photo has blown-out shadows. Of course, you can have both of these situations in the same photo.
In the photo below you can see that the vast majority of the image is very dark and the histogram shows that with a large spike on the left. In the upper right corner however, there is a section of the sky that is pure white and has lost detail. You can see that in the smaller (but tall) spike on the very right of the histogram. This is a great example of what NOT to do, but at times it is unavoidable. (We’ll be covering how to handle this type of exposure challenge later in the year.)
The human eye does not easily forgive the loss of detail in the lightest parts of a photo and it is best to avoid clipped highlights unless your goal is to purposefully make a gray sky look white. The human eye is more forgiving of clipped shadows, but don’t expect to be able to lighten those shadows to pull out any detail in post. It is best to avoid clipping on both ends of the histogram!
I encourage you to play and experiment with a bunch of different photos this week. I’ll be referring to histograms throughout my challenges for the rest of the year so you’ll want to get comfortable with them. If you want to read more about them, here are some helpful articles. Remember we’re focusing on the Luminosity Histogram in your camera, not in post-processing (though the concept is the same).
The challenge this week is to take and post a well-exposed photo and also post the histogram in the comments:
- Take your photo OUTDOORS during daylight hours and do not include any sky in your photo. (Sometimes sky can throw off the exposure. We’ll work on that in a future challenge.) If you have sun, I encourage you to take a photo both in sun and in shade to see how that affects your exposure (and histogram).
- The actual subject is wide open this week, but don’t forget all of the other rules for good composition, depth-of-field, etc. This might be a good week for macro since you can’t have the sky in your image.
- Post-processing is fine, but the goal is to get the exposure as perfect in camera as you can. If you do post-process, it would be interesting to see both the before and after histograms for your image.
What you will need to complete your challenge:
- A camera with the ability to show a Luminosity Histogram when reviewing photos on the LCD –or– a phone app which does the same. Here are some iPhone apps and here are some Android apps. (Be sure to read the app details to make sure it has a histogram. a “live histogram” means that the histogram is active while you take the photo, but may not be viewable afterwards. If that’s the case, you can simply take a screenshot to capture the histogram while your camera app is on.)
- Knowledge of how to change the exposure in your camera or camera app. This may be needed if you find that your histogram is not optimal and you need to adjust your exposure. If you don’t know how to do this, look up “exposure compensation” in the manual for your camera.
- Knowledge of how to take screenshots to capture the histogram of your photo. If you don’t know how to take screenshots (aka screen captures), you can do a search for your phone model or operating system (Windows or Apple) along with “screenshot” to find instructions for how to do it. Or you can simply take a photo of the histogram on your camera LCD or your computer screen.
The rules are pretty simple:
- Post one original photograph (Your Image) shot each week per theme posted on this blog to Google+, Facebook, or Flickr (or all three). Tag the photo #photochallenge and #photochallenge2017
- The shot should be a new shot you took for the current weekly theme, not something from your back catalog or someone else’s image.
- The posted image should be a still image or an animated GIF, not a video.
- Don’t leave home without your camera. Participating in the 2017 PhotoChallenge is fun and easy.