HDR is the acronym for “High Dynamic Range“, it is a technique used in photography, video and in some cases in video games to represent a wider range of brightness than standard imaging techniques can offer.
What is HDR used for?
There are two main areas where HDR is relevant:
- Photography: In photography, the HDR technique often involves taking several photos of the same scene with different exposures (usually one normal, one underexposed, and one overexposed) and then combining them into a single image. This combination results in a photo that better captures the shadows and highlights, showing more detail in both areas.
- Screens and video: In terms of displays (such as TVs and monitors) and video content, HDR refers to the ability to display a wider range of brightness, allowing bright whites and deep blacks to be rendered with more detail. When viewing HDR content on a compatible device, viewers may notice richer colors and improved contrast compared to standard dynamic range (SDR) content.
Differences between HDR and SDR
Both HDR and SDR (Standard Dynamic Range) refer to the representation and ability of an image to show detail in light and dark areas. In the following, we will describe the main differences between HDR and SDR:
- HDR: Can represent a wider range of brightness, allowing bright areas of an image to appear much brighter and dark areas to appear darker, without losing detail at either end.
- SDR: Has a more limited brightness range. Very bright or dark areas may lose detail and look “burned out” or overly shaded.
- HDR: Often associated with greater color depth, such as 10 bits or 12 bits per channel. This translates to billions of colors, allowing for smoother gradations and more accurate color representation.
- SDR: Typically uses a color depth of 8 bits per channel, which translates to 16.7 million colors.
- HDR: Can show significantly higher contrast between the brightest and darkest areas of an image. This can result in images that feel more three-dimensional and realistic.
- SDR: Has more limited contrast, which can make images feel flatter compared to HDR.
- HDR: Some HDR formats, such as Dolby Vision, use dynamic metadata that can adjust the image on a frame-by-frame basis according to the capabilities of the TV or monitor.
- SDR: Does not use metadata to adjust the image presentation.
Compatibility and Content
- HDR: Requires compatible hardware and content. This means that both the display device (such as a TV or monitor) and the content (such as a movie or video game) must support HDR to take advantage of its benefits.
- SDR: Is the traditional content and display standard and is broadly compatible with most devices and content.
- HDR: By offering more detail in both shadows and highlights, it can offer a more immersive and realistic visual experience.
- SDR: While it can offer excellent image quality, it does not have the ability to render the same amount of detail in high contrast scenes as HDR.
High Dynamic Range in Photography
The typical HDR process in photography involves taking several exposures of the same scene: one normal exposure, one or more underexposed (darker) and one or more overexposed (lighter). These images are then combined into a single image using specialized software. Today, both modern cameras and smartphones offer the possibility to take HDR pictures directly.
The goal is to capture details in the shadows and in the illuminated areas of a scene that, in a single exposure, might be too dark or too bright.
When done correctly, HDR photography can produce images that are more representative of what the human eye perceives in high-contrast scenes.
However, when overdone, it can lead to images that have an unrealistic or “painterly” look, which may be desirable for certain artistic styles, but not for all.
Considerations when taking HDR photographs
- Motion: Since multiple exposures are required, scenes with a lot of motion may not be ideal for HDR because they can result in “ghosting” images where an object moved between exposures.
- Camera: It is beneficial to use a camera that allows manual exposure adjustment and often has an automatic exposure bracketing (AEB) feature to facilitate multiple images.
- Tripod: Since images must line up perfectly, it is advisable to use a tripod to ensure that multiple exposures overlap properly.
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