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PD IEC TR 62935 pdf free download

PD IEC TR 62935 pdf free download.Measurement methods一 High dynamic range video.
4 Overview
4.1 Historical background
Still and moving pictures were initially captured and displayed with chemical processes, typically on film. The dynamic range varied by process and was limited by the maximum density achievable on the reproduction medium for representation of dark areas and by the minimum density achievable on the reproduction medium in representation of bright areas. Though there are hard limits with this technology, the processes involved resulted in the limits being approached gradually, with dynamic range expansion in the mid-tones, and dynamic range compression at the extremes.
Electronic images were initially captured and displayed using analogue means. Electronic noise limits the representation of dark areas and defined limits can clip the bright areas. Though a wire can carry much more than a 1 V signal (which represents 100 % white in some systems), various equipment in the processing chain might apply a hard clip. There is no natural compression as the signal approaches the white limit. Dynamic range compression is generally performed in the camera or in post-production with specialized equipment.
Today, most image capture, storage, and processing is based on digital technology. Dark details are limited by the noise and quantization error. White levels have a hard limit at the defined maximum white code value. Similar to analogue electronic techniques, dynamic range expansion in the mid-tones and compression at the extremes is performed by in-camera processing or in post-production.
Picture levels were standardized during the analogue time frame. Peak white for displays was defined as 48 cd/m2 for the cinema and 100 cd/rn2 for video presentation in mastering suites under controlled, low-level lighting conditions. These standardized levels were retained during and after the transition from analogue to digital equipment and techniques.
NOTE Consumer televisions have higher peak luminance, typically around 350 cd/rn2, in order to allow for bright viewing conditions.
4.2 Scene versus display ranges
Images are captured in a variety of conditions — from the dark reaches of Pluto to the intense light levels of the sun. The captured ranges of these images are normalized by controlling exposure levels. The high dynamic range system covered by this document is not intended to capture Pluto and the Sun at a single exposure image; however, an HDR system allows the captured range of those two separate images to include deeper black levels above the noise level and brighter white levels without clipping. An HDR system preserves those larger ranges through display to the viewer. This requires higher bit-depths, displays capable of higher luminance peaks, and carefully designed transfer functions to optimize the relationship between signal and presentation.
In essence, HDR relates to a system and signal definition that can represent an increased dark to bright range of a high dynamic range display, rather than trying to capture the full- range of extreme luminance differences found in nature.
A display with an increased dynamic range enables a fuller representation of the scene. Today, highly controlled scene lighting is generally used to keep faces bright, limit overly bright areas that would otherwise be “blown out”, and to light dark areas such that textures remain visible. In addition, electronic dynamic range compression is used to ensure that the information is well-represented by the signal. In naturally lit scenes, such as in sports, news, and documentaries, heavy dynamic range compression is often used and/or the signal is clipped, given that the lighting is generally not under the control of the content creator. For today’s SDR video systems, the content creator shall balance clipping at the extremes with making images dull through strong lighting or electronic compression.
For high-value content, adjustment of the dynamic range and colours can be controlled separately in various spatial regions of each frame by using dynamic masks. Image grading with dynamic masks can be complex and time consuming and is not practical in some situations, like live sports broadcasts and electronic news gathering.
On the other hand, with an HDR system, the content creator can preserve bright, specular highlights, source lighting, and sunlit areas with minimal clipping while also presenting welldisplayed faces and deeply dark textures. The result can be a more compelling visual experience than offered by SDR systems. The result can also be more representative of reality and can reduce the need for time-consuming, manual adjustments.
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