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Re: HDR question

Re: HDR question


alister@...
 

To make an image appear perceptually like the scene to a viewer, you do not want the luminance of the screen to be proportional to the luminance of the scene. You require what is referred to as "picture rendering" applied. This is the function of the RRT in the ACES block diagram, or the 1.2 "system gamma" of traditional video, to give two examples.

I’m fully familiar with viewing environments etc and the examples above assume that the viewing environment is different to the scene and that the monitors contrast range is significantly less than the scenes contrast range. But if we are talking about a monitor that can match the brightness and contrast of a scene, and if that monitor was placed into the scene the contrast range and perceived range of both could be matched. Display contrast is no different to scene contrast. Yes, viewing environment changes how we perceive an image (or a scene) relative to the ambient environment, but this is no different to looking through a small window at an exterior from inside a dark room. The brightness of the room will alter our perception of how bright it is outside.

So if a monitor can manage 8 stops and the scene is 8 stops and if the brightness of the monitor can match the brightness of the scene, in the same environment both will look the same. So to say that monitor contrast and scene contrast are different things is not correct. It is the viewing environments that are different and it is the difference in the viewing environment that changes the perception of the image, not differences in the contrast ratios of monitors. Unless I’m greatly mistaken and my whole knowledge of contrast and brightness is flawed.

Alister Chapman

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On 16 Mar 2018, at 15:02, Nick Shaw <nick@...> wrote:

On 16 Mar 2018, at 13:19, alister@... wrote:

Nick, could you enlighten me as to how the contrast ratio of a display is different to the contrast ratio of a scene, surely a ratio is a ratio, if a screen can show 10:1 and a scene is 10:1 are these ratios not the same?

A scene and display contrast ratio of e.g. 10:1 may be numerically the same, but they are not perceptually the same, because there is a difference in both the absolute luminance and the viewing environment.

To make an image appear perceptually like the scene to a viewer, you do not want the luminance of the screen to be proportional to the luminance of the scene. You require what is referred to as "picture rendering" applied. This is the function of the RRT in the ACES block diagram, or the 1.2 "system gamma" of traditional video, to give two examples.

Nick Shaw
Workflow Consultant
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Suite 87
30 Red Lion Street
Richmond
Surrey TW9 1RB
UK

+44 (0)7778 217 555

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