视频与电视工程革命：高清图形与电视融合

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"《标准视频和电视工程手册》第四版是一本全面深入探讨视频与电视工程技术的专业文档，它回顾了自早期电子计算机时代以来的技术变迁，强调了科技进步对日常生活和相关产业的巨大影响。书中指出，早期的电子计算机体积庞大、能耗巨大，与现今的微型化和高度集成形成鲜明对比，例如一个指甲大小的硅片就能构建整台计算机，且价格低廉。手册的核心部分关注于当前视频技术的两大关键领域：高分辨率计算机图形和高清晰度电视。这两个领域的发展相互交织，推动着通信行业的革新。随着消费者对电子产品的不断追求，个人电脑图形处理能力和高清视频体验的需求日益增长，视频成像技术在这个变革中的角色愈发凸显。在高分辨率计算机图形方面，本书可能涵盖了深度学习、虚拟现实（VR）、增强现实（AR）等前沿技术的应用，以及这些技术如何通过提升图像质量、交互性和真实感来重塑用户体验。而高清晰度电视则涉及到信号处理、显示技术、色彩校准等方面，以及新一代4K、8K甚至更高的分辨率标准。此外，手册还可能讨论了数字化视频编码、传输、存储和解码的最新进展，如H.264、HEVC（高效视频编码）等编解码标准，以及HDR（高动态范围）和Dolby Vision等高级显示技术。同时，对于网络电视、流媒体服务和互联网电视的兴起，以及它们对传统电视广播模式的挑战和融合，手册也会有所阐述。《标准视频和电视工程手册》第四版不仅提供了技术基础，还展望了未来发展趋势，是视频与电视工程师、技术研究者和行业从业人员不可或缺的参考资源。"

1-16 Light, Vision, and Photometry

takes place. Reds tend to become darker in approaching scotopic levels; greens and blues tend to

become relatively lighter.

Luminance

Brightness is a term used to describe one of the characteristics of appearance of a source of radi-

ant flux or of an object from which radiant flux is being reflected or transmitted. Brightness

specifications of two or more sources of radiant flux should be indicative of their actual relative

appearances. These appearances will greatly depend upon the viewing conditions, including the

state of adaptation of the observer’s eye.

Luminance, as previously indicated, is a psychophysical analog of brightness. It is subject to

physical determination, independent of particular viewing and adaptation conditions. Because it

is an analog of brightness, however, it is defined to relate as closely as possible to brightness.

The best established measure of the relative brightnesses of different spectral stimuli is the

luminosity function. In evaluating the luminance of a source of radiant flux consisting of many

wavelengths of light, the amounts of radiant flux at the different wavelengths are weighted by the

luminosity function. This converts radiant flux to luminous flux. As used in photometry, the term

luminance applies only to extended sources of light, not to point sources. For a given amount

(and quality) of radiant flux reaching the eye, brightness will vary inversely with the effective

area of the source.

Luminance is described in terms of luminous flux per unit projected area of the source. The

greater the concentration of flux in the angle of view of a source, the brighter it appears. There-

fore, luminance is expressed in terms of amounts of flux per unit solid angle or steradian.

In considering the relative luminances of various objects of a scene to be captured and repro-

duced by a video system, it is convenient to normalize the luminance values so that the “white”

in the region of principal illumination has a relative luminance value of 1.00. The relative lumi-

nance of any other object then becomes the ratio of its luminance to that of the white. This white

is an object of highly diffusing surface with high and uniform reflectance throughout the visible

spectrum. For purposes of computation, it may be idealized to have 100 percent reflectance and

perfect diffusion.

Luminance Discrimination

If an area of luminance B is viewed side by side with an equal area of luminance B + ∆B, a value

of ∆B may be established for which the brightnesses of the two areas are just noticeably different.

The ratio of ∆B/B is known as Weber’s fraction. The statement that this ratio is a constant, inde-

pendent of B, is known as Weber’s law.

Strictly speaking, the value of Weber’s fraction is not independent of B. Furthermore, its value

depends considerably on the viewer’s state of adaptation. Values as determined for a dark-field

surround are shown in Figure 1.1.7. It is seen that, at very low intensities, the value of ∆B/B is

relatively large; that is, relatively large values of ∆B, as compared with B, are necessary for dis-

crimination. A relatively constant value of roughly 0.02 is maintained through a brightness range

of about 1 to 300 cd/m

. The slight rise in the value of ∆B/B at high intensities as given in the

graph may indicate lack of complete adaptation to the stimuli being compared.

The plot of ∆B/B as a function of B will change significantly if the comparisons between the

two fields are made with something other than a dark surround. The greatest changes are for

luminances below the adapting field. The loss of power of discrimination proceeds rapidly for

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Light and the Visual Mechanism

1-18 Light, Vision, and Photometry

Visual acuity may be measured in terms of the visual angle subtended by the smallest detail in

an object that is visible. The Landolt ring is one type of test object frequently employed. The

ring, which has a segment cut from it, is shown in any one of four orientations, with the opening

at the top or bottom, or on the right or left side. The observer identifies the location of this open-

ing. The visual angle subtended by the opening that can be properly located 50 percent of the

time is a measure of visual acuity.

Test-object illuminance, contrast between the test object and its background, time of viewing,

and other factors greatly affect visual-acuity measurements. Up to a visual distance of about 20 ft

(6 m), acuity is partially a function of distance, because of changes in the shape of the eye lens

when focusing. Beyond 20 ft, it remains relatively constant. Visual acuity is highest for foveal

vision, dropping off rapidly for retinal areas outside the fovea.

A black line on a light background is visible if it has a visual angle no greater than 0.5 s. This

is not, however, a true measure of visual acuity. For visual-acuity tests of the type described, nor-

mal vision, corresponding to a Snellen 20/20 rating, represents an angular discrimination of

about 1 min. Separations between adjacent cones in the fovea and resolving-power limitations of

the eye lens give theoretical visual-acuity values of about this same magnitude.

The extent to which a picture medium, such as a photographic or a video system, can repro-

duce fine detail is expressed in terms of resolving power or resolution. Resolution is a measure

of the distance between two fine lines in the reproduced image that are visually distinct. The

image is examined under the best possible conditions of viewing, including magnification.

Two types of test charts are commonly employed in determining resolving power, either a

wedge of radial lines or groups of parallel lines at different pitches for each group. For either

type of chart, the spaces between pairs of lines usually are made equal to the line widths. Figure

1.1.8 shows a test signal electronically generated by a video measuring test set.

Resolution in photography is usually expressed as the maximum number of lines (counting

only the black ones or only the white ones) per millimeter that can be distinguished from one

another. In addition to the photographic material itself, measured values of resolving power

depend upon a number of factors. The most important ones typically are:

• Density differences between the black and the white lines of the test chart photographed

• Sharpness of focus of the test-chart image during exposure

• Contrast to which the photographic image is developed

• Composition of the developer

Sharpness of focus depends upon the general quality of the focusing lens, image and object

distances from the lens, and the part of the projected field where the image lies. In determining

the resolving power of a photographic negative or positive material, the test chart employed gen-

erally has a high-density difference, such as 3.0, between the black-and-white lines. A high-qual-

ity lens is used, the projected field is limited, and focusing is critically adjusted. Under these

conditions, ordinary black-and-white photographic materials generally have resolving powers in

the range of 30 to 200 line-pairs per millimeter. Special photographic materials are available with

resolving powers greater than 1000 line-pairs per millimeter.

Resolution in a video system is expressed in terms of the maximum number of lines (counting

both black and white) that are discernible when viewing a test chart. The value of horizontal

(vertical lines) or vertical (horizontal lines) resolution is the number of lines equal to the dimen-

sion of the raster. Vertical resolution in a well-adjusted system equals the number of scanning

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Light and the Visual Mechanism

1-20 Light, Vision, and Photometry

the greater the sharpness of the picture. Sharpness is, naturally, related to the transient curve in

the image across an edge. The average gradient and the total density difference appear to be the

most important characteristics. No physical measure has been devised, however, that predicts the

sharpness (appearance) of an image in all cases.

Picture resolution and sharpness are to some extent interrelated, but they are by no means per-

fectly correlated. Pictures ranked according to resolution measures may be rated somewhat dif-

ferently on the basis of sharpness. Both resolution and sharpness are related to the more general

characteristic of picture definition. For pictures in which, under particular viewing conditions,

effective resolution is limited by the visual acuity of the eye rather than by picture resolution,

sharpness is probably a good indication of picture definition. If visual acuity is not the limiting

factor, however, picture definition depends to an appreciable extent on both resolution and sharp-

ness.

1.1.4b Response to Intermittent Excitation

The brightness sensation resulting from a single, short flash of light is a function of the duration

of the flash and its intensity. For low-intensity flashes near the threshold of vision, stimuli of

shorter duration than about 1/5 s are not seen at their full intensity. Their apparent intensities are

nearly proportional to the action times of the stimuli.

With increasing intensity of the stimulus, the time necessary for the resulting sensation to

reach its maximum becomes shorter and shorter. A stimulus of 5 mL reaches its maximum

apparent intensity in about 1/10 s; a stimulus of 1000 mL reaches its maximum value in less than

1/20 s. Also, for higher intensities, there is a brightness overshooting effect. For stimulus times

longer than what is necessary for the maximum effect, the apparent brightness of the flash is

decreased. A 1000 mL flash of 1/20 s will appear to be almost twice as bright as a flash of the

same intensity that continues for 1/5 s. These effects are essentially the same for colors of equal

luminances, independent of their chromatic characteristics.

Intermittent excitations at low frequencies are seen as successive individual light flashes.

With increased frequency, the flashes appear to merge into one another, giving a coarse, pulsat-

ing flicker effect. Further increases in frequency result in finer and finer pulsations until, at a suf-

ficiently high frequency, the flicker effect disappears.

The lowest frequency at which flicker is not seen is called the critical fusion frequency or sim-

ply the critical frequency. Over a wide range of stimuli luminances, the critical fusion frequency

is linearly related to the logarithm of luminance. This relationship is called the Ferry-Porter law.

Critical frequencies for several different wavelengths of light are plotted as functions of retinal

illumination (trolands) in Figure 1.1.9. The second abscissa scale is plotted in terms of lumi-

nance, assuming a pupillary diameter of about 3 mm. At low luminances, critical frequencies dif-

fer for different wavelengths, being lowest for stimuli near the red end of the spectrum and

highest for stimuli near the blue end. Above a retinal illumination of about 10 trolands (0.4

ft⋅ L), the critical frequency is independent of wavelength. This is in the critical frequency range

above approximately 18 Hz.

The critical fusion frequency increases approximately logarithmically with increase in retinal

area illuminated. It is higher for retinal areas outside the fovea than for those inside, although

fatigue to flicker effects is rapid outside the fovea.

Intermittent stimulations sometimes result from rapid alternations between two color stimuli,

rather than between one color stimulus and complete darkness. The critical frequency for such

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Light and the Visual Mechanism

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