Everyone did a great job in our last histogram challenge! However, I noticed some confusion in the comments that I thought would make for a good follow-on challenge. Before we go any further though, I want to reiterate that the shape of the histogram is not important. There seemed to be some confusion about this. The truth is that there is no ideal shape for a histogram. What is important is that the width of the histogram should typically span the entire tonal range without blocking up against either side. (There are of course exceptions to this rule and we’ll explore some of those later in the year.)
Some of you followed this guidance perfectly in the last histogram challenge and yet you felt your image looked overexposed. You’ll be happy to know your eyes were not deceiving you! The answer can be found in the RGB (colored) histograms. In my last challenge I asked you to focus solely on the Luminosity histogram. That works fine for most photos, but can be inadequate for photos with a strong color cast (such as a sunset) or a predominant color (such as a red flower) as in the example below:
Hopefully the above photo looks overexposed to you. The red tones look blotchy without a lot of detail. However the Luminosity histogram looks fine – maybe even a bit underexposed. To figure out this apparent discrepancy, let’s take a look at the individual RGB histograms. (The RGB histograms give us information about the individual red, green and blue colors that make up every color in your photo.) It doesn’t take a whole lot of sleuthing to discover that the Red histogram has a spike at the far right side, i.e. detail is blown out in the red tones of the photo.
Blown out detail in the red tones is a fairly common issue with digital cameras. Luckily it’s easy to adjust for it once you know how to identify the problem. If you are ever concerned that you’ve lost detail in your photo, take a look at the RGB histograms. If you see a spike on either side of any of the histogram, you’ve found the culprit. To correct the issue, you simply need to adjust the exposure compensation on your camera until you no longer have any spikes blocked up against the sides of the histograms.
Note: The spike on the left side of the histograms above is on purpose. This is one of those exceptions to the rule that I mentioned above. In this image I wanted the background to be solid black, i.e. no detail. So in this case, the spike tells me that I achieved that effect. The important aspect of the histograms above is that there are no spikes at the far right side of the histograms, so no detail has been lost in the lightest parts of the image.
Optional info: If you’d like to know the technical details behind why the Luminosity histogram sometimes fails to give a complete picture, read on. If not, skip down to the next line of asterisks for this week’s challenge. This is not required reading. 😉
To better understand why the Luminosity and Red histograms look so different, let’s compare the color and grayscale versions of the overexposed photo. In particular, focus on the two areas where the red detail is most blown out.
If we look at the gray (luminosity) value of those two points, it should be obvious that they are squarely in the darker mid-tones, i.e. nowhere near white.
If you think about it, this makes sense. Imagine a red color and then imagine that same tone in B&W. It would not be white or anywhere close to white, right? That is why the Luminosity histogram is insufficient as the only tool for determining proper exposure. The Luminosity histogram reflects only the gray values of an image, but it is entirely possible that a single color may get blown out even though the color itself is in the middle of the Luminosity range. Luckily our cameras give us the tools we need to spot this problem so that we can make adjustments while we’re taking our photos: the RGB histograms.
If you haven’t already guessed, the challenge this week is to take a photo of something RED and also post both the Luminosity and Red histograms in the comments:
- At the very least, the color red should dominate the photo. If desired, it might completely fill the frame.
- Think “bright red”. While there are some stunning images with deep red tones, this week I want you to focus on making the red tones as bright as possible without losing detail.
- You will have an easier time if your red object is not shiny, but your choice of subject is up to you.
- Please post both the Luminosity and Red histograms in the comments under your photo. (You can post the Green and Blue histograms as well if they are part of the same display as the Red histogram.)
What you will need to complete your challenge:
- A camera with the ability to show the RGB histograms when reviewing photos on the LCD –or– a phone app which does the same. Some cameras show the RGB histograms right along with the Luminosity histogram, but other cameras show them on a different screen. You’ll need to look in the instructions for your camera. 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.
- The easiest way to capture the histograms on your camera LCD is to simply take a photo with another camera.
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.