Mike Chan
Mike Chan

Mike is part of the Canon Digital Learning Center team as a Senior Technical Specialist providing Online Educational resources to professional and advanced amateur photographers.

Monitoring Exposure from Histograms to Waveforms

February 03, 2017

Many HDSLR shooters (including myself) have been using histograms to judge exposure in our images. We have all looked for the ideal bell curve along the histogram, while avoiding crushed blacks to the left and clipped highlights to the far right. As we move out of DSLR video and into professional video camera systems, such as the XA, XF, XC and Cinema line, other tools to judge exposure have replaced our histograms.

There are several tools to judge exposure but I will only talk about the one that looks the most familiar, the waveform monitor. Waveforms work in a unit of measurement called an IRE, which stands for Institute of Radio Engineers that created the standard (now known as the Institute of Electrical and Electronics Engineers, IEEE). This was developed during the dawn of B&W television, where a waveform monitor was an analog device in which the video signal was filtered and amplified, which in turn sent voltages that caused a vertical spike in a cathode ray tube or CRT.

Waveforms are very similar to histograms in that they measure the luminance value of a scene from dark. Instead of seeing the overall luminance value across a scene from left to right like a histogram, waveforms measure luminance on the vertical axis as the horizontal axis is free to measure each PART of the scene from left to right.

In the example above, we can see the subject is exposed on a bright background. The histogram shows the luminance level of the scene as a whole , so it indicates that this scene is somewhat overexposed. What if we didn’t care about the surroundings and only cared about the exposure of the subject in the middle? You CAN do that by opening up the iris or raising the ISO, but then you have no idea what the exposure of the subject is, as the histogram will only show that your highlights are blown out. When you monitor the same scene on a waveform, you can see that it dips where the subject is because it’s reading the entire scene from left to right. From there, you can tell how much you need to open up to before you blow out the highlights and also how much more light you need to add to the subject.

Waveforms are a great transition if you are coming from a HDSLR camera or mixing HDSLR and Cinema EOS cameras on set, as your operators and DP can ensure that everything looks consistent among all cameras. If your HDSLR does not have waveforms in it, some external field monitors have them built in as well.

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