What is IRE?

Determine Your Exposure Levels When Filming in Log

What is IRE?

For many new filmmakers, the term IRE can be confusing. However, IRE is actually quite simple to understand. In short, IRE is used to determine the brightness levels of a video signal. In simpler terms, it measures the brightness or darkness of different parts of a video image, allowing you to properly expose and adjust the footage.

In the context of HDR (High Dynamic Range) footage, IRE refers to the measurement of peak brightness. The IRE scale ranges from 0 to 100, with 0 representing complete black and 100 representing the brightest white. By measuring the IRE level, we can determine the dynamic range of brightness that can be displayed in a video signal. This is important because it allows us to accurately represent the full range of colors and details in a scene, from the deepest shadows to the brightest highlights. Therefore, understanding IRE and its role in HDR footage is crucial for achieving optimal visual quality in video production. (Technically, the range of IRE in HDR extends up to 10,000 nits, while in SDR it reaches up to 100 nits.)

The reason this is important in post-production is that it determines the brightness levels of the footage are within the appropriate range for display on televisions. This ensures that your film will have a proper exposure and a visually pleasing appearance.

IRE values are often referenced in relation to 18% Gray to assist creators in determining the appropriate exposure levels for their footage. For instance, 18% gray corresponds to an IRE value of approximately 41-42. IRE values are essential in achieving accurate and well-balanced brightness levels in video content. 18% gray is often used as a standard reference point because it represents the average brightness in a scene.

Filming in Log

The IRE comes into play primarily when shooting in Log format. However, what can make things tricky is that each camera manufacturer rates their cameras differently in terms of IRE. Therefore, it is important to understand the specific IRE values for your camera when shooting in Log.

Camera manufacturers will determine their IRE to maximize dynamic range. This means that if they set their IRE at 37 (for 18% middle gray exposure), they expect you to slightly underexpose your footage (remember, 41-42 is typically where 18% middle gray IRE should be) in order to get the most out of the dynamic range.

This can create problems, however, if you want to keep your shadows clean and noise-free.

Determining Exposure

At Gamut, we have established our own IRE levels for each specific Log curve to optimize shadow cleanliness and ensure even balance in your footage. In each of our BaseLUTs, we provide a guide on IRE/exposure levels to assist you in maximizing the potential of your footage.

Regardless of whether you use Gamut BaseLUTs to convert your footage, it is important to check your conversion IRE levels. This will help you determine the optimal exposure levels for your version of Log footage, allowing you to maximize dynamic range, minimize highlight clipping, and protect the shadows.