High Dynamic Range: An Introduction

Editor's Notes

• #9: 10 f-stops = a difference of 210 = 1024: 1 contrast ratio. 14 f-stops = a difference of 214 = 16,384: 1 contrast ratio. 16 f-stops = a difference of 216 = 65,536: 1 contrast ratio. 100,000:1 is normally regarded as approximately the range that the eye can see in a scene with no adaptation. 20 f-stops = a difference of 220 = 1,048,576: 1 contrast ratio. 1,000,000:1 is normally regarded as approximately the range that the eye can see in a scene with minimal (no noticeable) adaptation.
• #14: The candela per square metre (cd/m2) is the derived SI unit of luminance. The unit is based on the candela, the SI unit of luminous intensity, and the square metre, the SI unit of area. As a measure of light emitted per unit area, this unit is frequently used to specify the brightness of a display device.
• #19: “I would much rather have a dynamic 2K HDTV than more pixels. Something with great blacks or great HDR, that is more impactful. Resolution is only apparent when you are close” Fundamentally, the video expert believes that 4K is just the tip of the iceberg and the least impressive part of what we should soon be seeing with video display technology.
• #20: “I would much rather have a dynamic 2K HDTV than more pixels. Something with great blacks or great HDR, that is more impactful. Resolution is only apparent when you are close” Fundamentally, the video expert believes that 4K is just the tip of the iceberg and the least impressive part of what we should soon be seeing with video display technology.
• #23: Therefore the concept of dynamic range becomes more complicated, and depends on whether you are describing a capture device (such as a camera or scanner), a display device (such as a print or computer display), or the subject itself. In fact, another device not shown above is our eyes, which also have their own dynamic range.
• #24: Scenes with high variation in reflectivity, such as those containing black objects in addition to strong reflections, may actually have a greater dynamic range than scenes with large incident light variation. Photography under either scenario can easily exceed the dynamic range of your camera — particularly if the exposure is not spot on.
• #25: Photosites can be thought of as buckets which hold photons as if they were water. Therefore, if the bucket becomes too full, it will overflow. A photosite which overflows is said to have become saturated, and is therefore unable to discern between additional incoming photons — thereby defining the camera's white level.
• #26: Scanner express dynamic range in terms of density This is useful because it is conceptually similar to how pigments create tones in printed media, as shown below.
• #29: For example, a light bulb can have more than 10,000 cd/m2, surfaces lit in the sunlight can have brightness upwards of hundreds of thousands of cd/m2, while the night sky can be 0.005 cd/m2 or lower. In color reproduction, including computer graphics and photography, the gamut, or color gamut /ˈɡæmət/, is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a certain output device.
• #32: The human eye uses the pupil to allow it to see darker or brighter images. If the pupil gets smaller, then less light enters the eye. This means that the eye can look at brighter areas without overwhelming the eye with too much light. But this comes with a tradeoff: when the pupil is small, less light means that the eye cannot see dark areas as well. The total range from darkest to brightest visible at the same time does not change significantly for the eye, but the eye can adjust the pupil to optimize the overall viewing conditions and adjust to varying amounts of light.