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.


Rainbow Bouquet – Jeanie Sumrall-Ajero

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.


GUEST POST – TIME STACKING by Jeanie Sumrall-Ajero

I’ve been fascinated by time stacked images for some time now so it seemed like a great idea for a challenge. What is time stacking? Essentially it is a time lapse except all of the frames are layered on top of one another in just one image instead of creating a video. The technique is commonly used for astrophotography (star trails), car trails and waterfalls but it can also be use to create amazing landscape images.

Sunset - Time stacking example

Layering a series of landscape photos containing clouds gives a wonderful sense of movement to a landscape image. This image is a time stack of 56 photos taken 10 seconds apart. For colorful clouds, take photos of a sunset. (This technique won’t work very well at sunrise, so be sure to take photos at sunset if you want some color in your clouds.)

Wrath of a Thunderstorm

For those of you short on time or patience, you can use fewer photos in your time stack. This is just 15 photos taken 5 seconds apart. There are two elements that determine how smooth or jagged the movement in the clouds appears: (1) the amount of time between each shot and (2) how quickly the clouds are moving. If the clouds are moving quickly and you want a smooth look, you’ll need to take more photos. If the clouds are moving slowly, the interval between shots can be larger. Having said that, it’s nearly impossible to guess what your image will look like once all of the photos are stacked and that’s half the fun of it!

Time stacking example (29 photos)

Unfortunately, not everyone will have amazing clouds to photograph this week. Not to worry! In this photo my initial goal was to smooth out the water, but then I realized that I caught the gulls in flight as well. Not only did the size of the flock seem to grow, but their flight patterns in the sky seemingly appeared out of nowhere when I stacked the photos. This is a time stack of 29 photos taken in just 10 seconds, i.e. burst mode. (Note: If you want to try this technique with flying birds, you will need to find white birds or at least birds that are lighter than the sky behind them. It won’t work otherwise.) I included one of the photos used in the stacked image so that you can see the difference between a “normal” image and the stacked version of the same scene, particularly the water, the number of birds and the flight patterns of the birds in the sky.

Waterfall - Time stacking example

Another use of the time stacking technique is to fill out waterfalls or other moving water. If you find a waterfall that doesn’t have much water, you can make it look fuller by stacking a few photos together. Again I have provided both the stacked image (on top) and a single image from the stack. The difference is most visible in the water going over the large rock just to the left of center, but if you look closely you’ll see that the volume of water looks fuller throughout the stacked image.

Car trails - Time stacking example

Or you could stack a few photos of light trails from cars. It doesn’t take many photos to make a road look really busy! This image was created from four stacked photos.

Star trails - Time stacking example

And of course if you love astrophotography, this would be a great challenge to show off your skills with star trails. This image was created from three 15-minute exposures.

For more inspiration be sure to check out the amazing time stacked photos of Matt Molloy, a pioneer of using this technique for landscape photography: http://flic.kr/s/aHsjCgruXn (There is one of a smoke stack that I think is way cool!)


Taking the photos

  1. You’ll need a tripod. If you don’t have a tripod, you can search google for DIY tripods.
  2. For best results, use Manual Mode on your camera and set both the ISO and White Balance to something other than Auto. Basically you want all of the photos in your series to be taken with the exact same settings.
  3. Make sure your exposure it set to capture as much detail as possible in the lightest elements of your scene, i.e. don’t blow-out the highlights. It is the highlights that will be creating a pattern in your stacked image, so you want to capture as much detail in the light areas as possible.
  4. If you have an intervalometer feel free to use it, but for the purposes of this challenge I had just as much luck counting to 5 or 10 between my shots and taking the photos without an intervalometer. Regardless of the method you choose, be sure to be consistent with the time between each photo (especially for cloud photos – waterfalls and car trails are more forgiving).

Processing the photos

If you do not have Photoshop, I’ve put together a video tutorial explaining how to stack your photos in www.pixlr.com (a free online photo editor). The technique I show in the video should work with any photo editor as long as it supports layers and layer blending modes. I encourage you to watch it even if you have Photoshop since you might pick up a tip or two.

If you have Lightroom and Photoshop, there are numerous tutorials and videos available showing how to do time stacking.

In addition, Matt Molloy has written a tutorial explaining his technique at http://iso.500px.com/time-stack-photo-tutorial/. I encourage you to read through it for more details from his perspective.

When posting your photos this week, it would be fun to also post a single photo from your time stack as a comment so we can see the difference time stacking makes.


About the author: Jeanie Sumrall-Ajero is intensely curious about life and loves to explore it through the lens of her camera. She has dabbled in photography from time to time throughout her life, but it wasn’t until this past year when she took a semi-sabbatical from work that she decided to explore photography more seriously as a creative art form. Jeanie’s Flickr page can be found at www.flickr.com/photos/the-digital-jeanie/.