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September 2015

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www.postmagazine.com 37 POST SEPTEMBER 2015 Part I of Chris Bone's report on 4K and HDR ran in last month's issue of Post. Here, Bone picks up with a look at dynamic range … ynamic range" refers to the expression of contrast be- tween the darkest part of the image to the brightest part of the image, but it may also refer to images seen or flashed in a sequence, and because the viewer's iris state can also change, the perception of the dynamic range can change over time, depending on the way it is present- ed. In this regard, there is both a time and a spatial, compositional aspect to avoiding abrupt changes to dynamic range, and there is not nec- essarily an obvious ideal viewing en- vironment. While high dynamic range may be considered the next best desirable attribute for image capture, manipulation, and improving the perceived reality of subsequent im- age presentation, it is also a relative aspect of imaging. The expression of tone from dark to light is what our eyes generally have to adjust for in overall iris level, for functionality. The average reflectance values of general imaging have been determined to fall at 18 percent, which is propor- tionally relative to the brightness and the darkness and where the midpoint may be perceived. An ide- alized camera ISO rating provides a proportionally equal number of steps of brightness and darkness above and below the midpoint, based on average reflectance. However, the display of the image is not typically reciprocal to what the eye and cam- era sees, often underrepresenting the illumination levels the eye sees, or at least often underrepresenting the maximum brightness. Having a dis- play that could significantly express more orders of magnitude above and below this midrange than what has customarily been achieved in typical image viewing to date would constitute a characterization of high dynamic range. In terms of pure power function, the higher the display gamma is, the faster the brightness steps increase as one moves up the tone scale. For movie presentations, the current standard cinema luminance is set at 48 cd/m2, less than half of that which may be now used for television col- orist grading of approximately 30fL, or 100 cd/m2. Orders of magnitude above cinema luminance to accom- modate for additional dynamic range are theoretically more easily achieved when the starting point of peak white is lower, although the typical cinema gamma power curve average is steep- THE STATE OF THE ART FOR 4K AND HIGH DYNAMIC RANGE - PART II AS MUCH A VISION FROM THE PAST AS IT IS FOR THE FUTURE BY CHRIS BONE, CTO, VTP, WWW.MYVTP.COM 4K HDR PART II "D Dynamic range refers to the contrast between the darkest to the brightest part of an image. AND SPECIAL REPORT:

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