Histograms and Blinkies

Ok so I lied. In the last post I said that we would discuss exposure compensation next. Instead, we’re going to talk about a couple of in-camera tools that you can use to really nail the exposure in the field. I know everyone was probably waiting with bated breath to hear my take on why exposure compensation is so useful on fire scenes (and it is!), but I realized that a quick overview of blinkies and histograms would be helpful in understanding the hows and whys of exposure compensation.

Histograms and blinkies are exposure tools we can use in the field to quickly review a photo we’ve just taken to make sure we’re getting good exposure. They allow us to tell at a glance if we’ve hit the Goldilocks zone — not too dark, not too bright — just right.

Why They're Useful

Why, you might ask, would we need tools for this? Why not just look at the image in the LCD screen? There are several reasons. First, the LCD screens on the back of cameras are small and can be difficult to see. Especially for investigators of a certain age. When your hands are dirty with fire debris, it’s no fun to have to dig reading glasses out of a pocket every time you want to check the exposure. Secondly, LCD displays can fool us because the brightness of the screen doesn’t always match the brightness of the image. LCD brightness can be adjusted according to the ambient lighting conditions. While this is a very useful feature, it can sometimes lead us astray. In bright sunlight or glare, an image might seem too dark on the LCD and lead us to think it’s underexposed, even though it is not. Conversely, if we are in a dark setting, or shooting at night, the LCD image can appear very bright, even if the image is actually underexposed.

Image playback at lowest brightness setting.

Image playback on the highest brightness setting.

Histograms and blinkies give us two ways to see at a glance if we’re getting the exposure right. They work independent of the LCD brightness. They can be seen even with a little glare on the screen. Best of all, I can see them without putting on my reading glasses!

Histograms

Camera displays have options to display either RGB (Red/Green/Blue) color channel histograms, or luminosity (brightness) histograms. While RGB histograms can be used in the field, they are most often used for color editing in post-process. The luminosity histogram on the other hand is a very helpful tool in the field. This type of histogram is a essentially bar graph that represents the distribution of pixel brightness in an image. Brightness values are placed on the X axis of the graph with the darkest value (pure black) all the way to the left. The tonal values, 256 in all, increase in brightness as they move to the right side of the graph. The brightest measurable value (pure white) is located on the far right of the X axis. Each pixel in the image is assigned a brightness value and that value is represented in one of the 256 columns of the histogram. These columns touch one another so that the data are presented as a continuous line of peaks and valleys. Black pixels are placed on the left end of the graph. White pixels on the right. All the others are placed in between according to their level of brightness. The Y axis of the graph describes the frequency with which that brightness level appears in the image.

The histogram gives the photog a visual representation of the overall exposure. The histogram is not affected by the brightness of the camera’s LCD display. Because it is displayed in black and white, the histogram is often easier to see in bright sunlight or when there is a glare on the screen.

Checking the exposure using the playback image alone can be tricky, especially in bright daylight. Are the bright areas properly exposed or blown out? It's much is easier to tell by looking at the histogram. This one is showing a good exposure. The highlights trail off and do not touch the right side of the histogram. Likewise, there is space between the left side of the graph and the shadow peaks, indicating that we have good detail in the shadows.

It's important to know that there is no “right” way for the histogram peaks to look. Exactly what shape the histogram takes is going to depend on the scene and subject we’re shooting. A scene heavy in middle tones will look like a hill or mountain standing at the center of the histogram, tapering to either end. A contrasty "high key" scene may have high peaks on the right and the left sides of the graph. A darkly colored subject (fire debris) may skew the histogram to the left. A brightly colored scene like a snowy field, will show lots of peaks on the right. That’s all ok. The key to checking the exposure with a histogram is to see that the peaks are not pushed all the way up against either end of the graph. If there’s a large peak touching either end of the histogram, it’s an indication that there is clipping.

Clipping

Clipping occurs when areas of the image are recorded as either pure black (shadow clipping) or pure white (highlight clipping). A little bit of clipping is common and may be no big deal. You may have some clipped details in the sky on a bright day, especially if your subject is backlit. You may have small areas of clipping in deep shadows in your photo. This type of clipping is usually not a problem. However, if large areas of the image are clipped, or if you clip the details on your subject, it can be a serious problem for your photo. This is because clipping is not fixable in post.

In most situations, if an image is under or overexposed in the field, we can still fix the image in post-processing. Editing software allows the photog to turn down highlights to recover details or to brighten underexposed areas of the photo. But this will only work if the camera records some details in these areas at the time of capture. When we clip part of an image, the camera will record no detail in that area. The clipped part will record as pure white or pure black and there will be no detail there to bring out in post-processing.

Histograms will show you if you have clipped part of your image. If you see in your histogram that data are touching either the right side or the left side of the graph, it's an indication that you’ve clipped something. The higher the end peak, the more clipping has occurred.

Highlight Clipping

Shadow Clipping

Learning to use histograms can take a little practice but it’s not difficult. The best way to learn is by looking at them. Turn on histograms in your camera’s menu so that they display along with the image during playback. After a while, you’ll be able to predict what the histogram for an image will look like before you even take the shot. Check the histogram after you shoot to see if it matches expectation. If it doesn't, you may need to change your exposure.

Clipping Example 1

This exposure looked ok in the playback image on the back of the camera but it was actually overexposed. Looking at the histogram could've shown that something was wrong with the exposure.

The histogram in Adobe Lightroom shows that the highlight peaks are touching the right side of the histogram. This indicates that the highlights were recorded as pure white.

Clipped highlights cannot be recovered in post-processing. Here, I've reduced the exposure by 2.5 stops. The image is darker but the label is still unreadable because no details were recorded in the highlights.

Clipping Example 2

In this macro shot of a GFCI receptacle the components on the left side are clipped.

Here, I've tried turning down the highlights as much as possible. The photo is darker in the clipped area but there is a lot of detail missing.

Clipping and Dynamic Range

In photography, dynamic range refers to the difference in brightness between the darkest area of the image and the brightest. Modern full frame cameras have a dynamic range of about 15 stops of light. As we discussed in the post on the exposure triangle going up one stop means doubling the amount of light. Going down a stop means reducing the amount of light by half. That means that with most full frame cameras if we begin with the maximum level of measurable brightness (a completely white image) we can half the amount of light 15 times before the camera records the scene as completely black. This is an impressive feat when compared to the dynamic range of film cameras or even older digital cameras, but digital cameras still fall short of the dynamic range we are able to perceive with our eyes. Comparing the dynamic range of cameras to the dynamic range of human vision is complicated and inexact. Even so, the comparison is helpful. Most sources estimate the dynamic range of the human eye at 20-30 stops of light. Whatever the number we use, the important takeaway is that the dynamic range of digital cameras is limited and is somewhat less that what we can see with our eyes. This can present challenges in high contrast scenes.

Some scenes that we need to shoot will exceed the dynamic range of the camera. When this happens, we will not be able to record all the details in the highlights and in the shadows in a single shot. Taking an image of a dark object against a bright background (fire debris in bright snow) or a bright object on a dark background (white evidence label on a charred floor) are good examples. When the brightness levels within the scene exceed the dynamic range of the camera, some clipping may be inevitable.* In these cases it's important to know what information is being clipped. If we are shooting a pole mounted transformer and we have clipping in the white clouds in the sky behind it, that's no big deal. If we are shooting the back of an appliance and we clip the model and serial number, it's a problem. One of the easiest ways to see where and what you are clipping is to turn on highlight alerts, AKA blikies.

This shot is maxing out the dynamic range of the camera. The bright sun on the front of the truck blew out the highlights. The angle of the sunlight caused the dashboard to be in deep shadow. The highlights are blown out. While the shadows aren't quite clipped, the interior of the truck is underexposed. To correct this shot we need more light inside the truck.

*There are things we can do to increase the dynamic range in our images such as HDR photography and in-camera dynamic range enhancement settings. We'll discuss those features in another article.

Blinkies

While histograms can take some getting used to, highlight alerts, also known as blinkies, are dead simple and are embedded right into the playback image. The alerts will cause clipped areas of the photo to flash or blink at you when the image is played back. Blinkies may flash black, red, or orange. Sony shooters sometimes refer to highlight alerts as "zebras" because their highlight alerts flash black and white stripes . Regardless of the color of the blinkie, their message is the same — “You’re clipping!” Almost every pro and enthusiast level camera has some form of highlight alert. Some mirrorless cameras go a step further and also give you shadow clipping alerts. My Olympus OMD-EM1, for instance, flashes blue in areas where the shadows are clipped.

One thing to keep in mind is that both blinkies and histograms are based on the JPG playback version of the image. This is true even if you shoot in RAW. Because of this, histograms and blinkies will be affected by JPG settings like image profile, white balance, and dynamic range enhancements like Active D-Lighting (Nikon) or Auto Lighting Optimizer (Canon). If you shoot in raw, it’s best to choose a flat or neutral image profile and turn off dynamic range enhancements.

RAW files have more dynamic range than JPGs so they typically will record more data in the shadows and the highlight areas. If you are a RAW shooter and you see small areas with blinkies, know that you may still be able to recover data from these areas in post processing. Of course there are limits. Even if you’re shooting in RAW you should take blinkies as an indication that you are pushing the limits as far as exposure goes.

The histogram in the image above shows clipping in both the highlights and the shadows. Since the shadow clipping is mostly around the edges of this exemplar hard drive, it's not a major concern. The highlights are another story. The blinkies are showing clipping on the manufacturer label. This photo needs to be re-shot.

In this image the weather head is properly exposed but we do have some highlight clipping as seen on the right side of the histogram. The blinkies show us that the clipping occurred on the roof gutter in the foreground of the image. I'd be fine with this shot.

Enabling Histograms and Blinkies

The exact method for enabling histograms and blinkies varies depending on the manufacturer. Cameras made by the same manufacturer may have different menu names and options. Even so, the process is usually similar to what you'll see below. If the following doesn't work for you, refer to your camera's manual. Or Google it.

Canon Mirrorless Cameras

To enable highlight alerts during playback

Press the MENU button.
Go to the Playback Menu (blue tab).
Look for Highlight Alert.
Set it to ENABLE.

To turn on Histogram During Playback

Histograms are usually on by default in playback, but if not:

MENU → Playback (Blue) Tab → Playback information display → Enable Histogram

Then:

Press Playback
Press INFO to cycle through display options until you see the histogram.
You can choose Brightness or RGB histograms.

Nikon Mirrorless Cameras

To enable highlight alerts during playback

Press the MENU button.
Go to the Playback Menu (triangle “play” icon).
Select Playback display options (sometimes “Playback display settings”).
Check/enable Highlights.
Press OK.

To turn on Histogram During Playback

This shows a histogram when reviewing images.

Press MENU
Go to the Playback Menu (▶ icon)
Select Playback display options
Check the box next to Histogram
Press OK

When reviewing images, press the up/down arrow to cycle displays until the histogram appears.

Canon DSLR Cameras

How to Turn On Highlight Alerts

Press the MENU button.
Navigate to the Playback tab (the blue tab with the triangle/play icon).
Look for:
- Highlight alert
- NOT Highlight tone priority. This is a different feature!
Select Highlight alert → ENABLE.

If you don’t see the option....

On some models the layout differs:

Entry-level models (Rebel T3–T8i / 1000D–850D)

Go to MENU → Playback (blue) tab → Highlight alert → Enable
(Sometimes it's under Playback Display Options.)

Mid-range / Semi-pro (70D, 80D, 90D, 7D series)

MENU → Playback → Highlight alert → Enable
Some models require opening Playback Display Options first.

Pro bodies (5D, 6D series)

Usually Playback Tab → Highlight alert directly.

How to Turn On Histograms on a Canon DSLR

1. Open the Playback Menu

Press MENU → go to the Playback (blue) tab.

2. Enable the Histogram Display

Look for one of these options (your camera will have one of them):

Option A: “Histogram display”

Go to: MENU → Playback → Histogram display
Choose Brightness or RGB

Option B: “Playback display options”

Go to: Playback Menu → Playback display options
Check Histogram (or Brightness/RGB Histogram)

Option C: “Info display options” (common on mid/high-end models)

Go to: Playback Menu → Info display options
Enable Histogram or Detailed Info

View the Histogram During Playback

Press ▶ Playback
Press the INFO button repeatedly
- Each press cycles through different screens
- Stop when the histogram appears (brightness or RGB)

Nikon DSLR Cameras

How to Turn On Highlight Alerts

Step 1 — Go to Playback Menu

Press MENU → navigate to the Playback Menu (the icon looks like a play button ▶).

Step 2 — Enable “Playback Display Options”

In the Playback Menu, select Playback display options.
Check the box for “Highlights”.

This activates the highlight alert overlay.

Step 3 — View Highlights During Image Playback

Press the Playback button to view a photo.
Press the UP/DOWN arrows on the multi-selector to cycle through different display screens.
Stop on the screen that shows flashing white or black areas — these are blown highlights.

Notes & Tips

Some models require pressing the LEFT/RIGHT arrows instead.
If you don’t see the “Highlights” checkbox, your model may call it “Overexposure warning.”

How to Turn On Histograms on a Nikon DSLR

Step 1 — Open the Playback Menu

Press MENU → go to the Playback Menu (▶ icon).

Step 2 — Enable Histogram Display

Look for one of the following options (your camera will have one of them):

A. “Playback display options”

MENU → Playback Menu
Select Playback display options
Check Histogram
- You may see two separate options:
  - RGB Histogram
  - Brightness Histogram

B. Older models may show:

Display Mode
Playback Display Mode

Check Histogram in that menu.

Step 3 — View Histogram During Playback

Press the Playback button to view a photo.
Press the Up/Down (or sometimes Left/Right) arrows on the multi-selector to cycle through the different display screens.
Stop when you reach the histogram screen.

You should now see:

Brightness histogram (single curve), or
RGB histogram (three-color curves)

Sony Mirrorless Cameras

How to Turn on Histograms (Sony Mirrorless)

In Shooting Mode (Live View Histogram)

Press MENU
Go to the Display/Auto Review or Custom Operation section (varies by model)
Find DISP Button → Monitor
Enable Histogram
Exit the menu
Press the DISP button while in shooting mode to cycle through screens until the histogram appears.

What this does:
Shows a live histogram on the LCD or EVF before you take the shot.

During Playback (Image Review Histogram)

Press Playback
Press the DISP button to cycle through display modes
Stop on the screen that shows the RGB histogram

How to Turn on Highlight Alerts (Sony Mirrorless)

Enable Zebras

Press MENU
Go to the Exposure/Color or Custom Settings tab
Select Zebra Display → On
Select Zebra Level
Recommended settings for photography:
- 100+ → warns when highlights are about to clip
- 100 → stricter warning (useful for protecting highlights)

Zebras only appear before you take the photo — not during playback.

Playback Highlight Warning

Some Sony cameras also show “blinkies” during playback:

Press Playback
Press DISP repeatedly until you see flashing highlights on blown-out areas.

(Not available on every model — older A6000-series bodies rely mainly on histograms for review.)

Conclusion

Blinkies and histograms are extremely useful tools. They allow you to quickly and easily check for proper exposure and are more reliable than looking at the playback image on the LCD alone. If you see clipping on the histogram or blinkies flashing at you on the playback image, it’s usually a good indication that you need to adjust the exposure. Back in the post on camera metering, we discussed ways to change the exposure by using different metering modes and by changing where we put the focus point. In the next post, we’ll discuss another, often easier method for tweaking your exposure — exposure compensation.

<<< Metering Modes

Exposure Compensation >>>

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