Acquisition

A person using a camera to acquire image data from a scene expects that when the acquired material is

displayed it will approximately match the appearance of the scene. Luminance of white in an outdoor scene might reach 30,000 cd·m-2, but it is rare to find an electronic display whose luminance exceeds

450 cd·m-2, and professional HD content mastering and approval is performed with a reference white around 100 cd·m-2. Linear transfer of the scene luminance to the display – in effect, scaling absolute luminance by a factor of 0.015 or 0.01 – won’t present the same appearance as the outdoor scene. The person using the camera expects an approximate apppearance match upon eventual display; consequently, picture rendering must be imposed. In HD, and in consumer still photography, rendering is imposed at the camera; in digital cinema and in professional (“raw”) still photography, rendering is imposed in postproduction.

Some people use the phrase “scene-to-screen” to describe the goal of delivering an accurate representation of scene luminance and colour to the display. Unless proper account is taken of appearance phenomena – that is, unless picture rendering is imposed – this effort is doomed to failure.

Consumer origination

Figure 2.5 summarizes consumer-originated video. Consumers may exercise creative control through signal processing after acquisition; however, picture rendering is imposed by algorithms in the camera. The camera is engineered to encode signals for presentation in the consumers’ living room. Studio origination is built on an assumption of viewing at 100 cd·m-2 in a dark surround (today, around 1%). Consumer camcorders incorporate picture rendering based upon comparable parameters.

Consumer electronics (CE) display

In the consumer electronics domain, there is a diversity of display devices (having different contrast ratios, different peak luminance values, and different colour gamuts), and there is a diversity of viewing environ-

Figure 2.5 Consumer origination of either still photographs or video has all of

the issues of image acquisition that I outlined in Figure 2.1, but consumers rarely process or review

imagery before distribution and typically exercise no control over the parameters of image capture or processing. Algorithms in the

camera impose picture rendering and incorporate the rendering into the image data. Those operations assume a certain display and viewing environment. That reference viewing environment is thereby incorporated (explicitly or implictly) into the image exchange standard.

ments (some bright, some dark; some having bright surround, some dim, and some dark).

Different consumer display devices have different default EOCFs. The EOCF for a particular product is preset at the factory in a manner suitable for the viewing conditions expected for that product. Traditional domestic television receivers had EOCFs approximating the 2.4-power function used in the studio; however, modern consumer receivers are considerably brighter than 100 cd·m-2 (up to 350 cd·m-2 today) and the higher brightness necessitates a somewhat lower value of gamma, today typically between 2.1 and 2.3. A home theatre projector used in a rather dark environment will have characteristics comparable to those of a studio reference display (see Reference display and viewing conditions, on page 427), and will typically have “gamma” of about 2.4. A PC has a default sRGB EOCF, with gamma of 2.2.

Consumer television receiver vendors commonly impose signal processing claimed to “improve” the image – often described by adjectives such as “naturalness” or “vividness.” However, the director may have thoughtful reasons for wanting the picture to look unnatural, pale, or noisy! Creative control is properly

Linear-light and

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