Computer graphics processing and selective visual display system – Display driving control circuitry – Intensity or color driving control
Reexamination Certificate
2001-08-28
2003-03-04
Bella, Matthew C. (Department: 2672)
Computer graphics processing and selective visual display system
Display driving control circuitry
Intensity or color driving control
C345S102000, C348S602000
Reexamination Certificate
active
06529212
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for automatically adjusting luminance and contrast of a display unit. Specifically, the present invention is directed to an apparatus and method that adjust luminance and contrast as functions of ambient and surround luminance.
BACKGROUND OF THE INVENTION
There are a variety of applications and devices in which a display unit is utilized to electronically display images. It is desirable to provide a display unit for such applications and devices that is capable of automatically adjusting luminance and contrast without the need for operator intervention. It is common, for example, to provide electronic cameras with image display units that must be utilized in a wide range of lighting conditions in which luminance levels vary greatly. Without some form of automatic adjustment, the operator must constantly change settings manually to compensate for changes in the lighting environment.
It has been well documented in the scientific literature that one's brightness and contrast perception of an image is significantly affected by the ambient and surround luminance in which it is viewed. See, for example, “Visibility of Transmissive Liquid Crystal Displays under Dynamic Lighting Conditions”, J. H. Krantz, Human Factors, 1992, 34(5), 615-632, the contents of which are herein incorporated by reference. Brightness is defined as the attribute of a visual sensation according to which an area appears to emit more or less light. Contrast is defined as the rate of change of the brightness of image elements as a function of the relative luminance of the same image elements in the original scene. Differences in these perceived attributes can be related to the operator's state of visual adaptation to the ambient and surround luminance. For example, as the ambient luminance increases, the user begins to gradually adapt to the new light level by: a) reducing the amount of light which enters the eye; and b) reducing the sensitivity of the light-sensitive elements of the eye. The light entering the eye from the display unit, however, is also correspondingly reduced, thereby causing the display unit to appear dimmer to the operator. In response to this effect, the luminance of the display unit needs to be increased to maintain the operator's perception of the displayed image. Conversely, as the ambient luminance decreases, the operator begins to gradually adapt by: a) increasing the amount of light that enters the eye; and b) by increasing the sensitivity of the light-sensitive elements of the eye. In this case, the light entering the eye from the display device unit is also increased, thereby causing the display unit to appear brighter to the operator. The luminance of the display unit must then be decreased to maintain the user's perception of the displayed image.
While the eye adapts to changes in ambient luminance, the process of adaptation is not directly reversible. Instead, the human eye requires a significant period of time to adapt to changes when ambient luminance is decreased and a much shorter period to adapt to increases in ambient luminance.
FIG. 1
, for example, illustrates a plot of the darkness adaptation effect showing the amount of time it takes for an individual to visually adapt to changes in ambient luminance. As illustrated in
FIG. 1
, several minutes are required before the sensitivity of the eye reaches its full level of adaptation when the ambient luminance is decreased.
FIG. 2
is a plot of the lightness adaptation effect showing the amount of time it takes for the eye to adapt to increased ambient luminance. As illustrated in
FIG. 2
, the eye's sensitivity changes dramatically over the first second after an increase in ambient luminance, continues to change significantly for a period of 20 to 30 seconds, and then changes very slightly thereafter.
It has also been shown that the perceived contrast of an image changes as the luminance of the image surround changes. The surround of an image is defined as the area around an image extending from its edge in all directions.
FIG. 3
is a plot which shows such an effect. The plot illustrates the relative brightness of image elements as a function of their relative luminances for an average, dim, and darkly illuminated surround, which shows that the perceived image contrast increases with increasing surround luminance and decreases with decreasing surround luminance.
It is also known that the physical luminance and contrast of the display unit will be affected by lighting conditions. Assuming that the display unit reflects light as if it were a perfectly Lambertian surface, it is known that the luminance of the display unit in any ambient environment can be analytically determined from the equation:
La=Ld+Lr
where La represents the luminance of the display unit in current ambient lighting conditions, Ld represents the luminance of the display unit in a perfectly dark environment, and Lr represents the reflected luminance of the display unit. If the amount of ambient illuminance is measured, Lr can be calculated from the equation:
Lr=I*R/&pgr;
where I is the ambient illuminance, R is the coefficient of reflection for the display device and &pgr; is the arithmetic constant PI. The contrast of the display device can be determined by calculating La for a dark pixel and La for a fully lit pixel on the display device and then calculating the ratio of these parameters.
Contrast of Display=
La
fully lit pixel
/La
dark pixel
It should be noted that while R will usually be constant for most display units, this parameter may differ for dark and lit pixels for some display units such as liquid crystal displays.
Still further, researchers have found that the optimum display luminance is a function of display illumination level and this relationship can generally be explained by the equation:
log
L
d
=a+b
log(
I
)
where L
d
is the display luminance, I is the illumination level, and a and b are constants fit to psychophysical data. See “The ABC's of Automatic Brightness Control”, R. Merrifield and L. D. Silverstein, SID 88 Digest, 1988, pgs. 178-180, the contents of which are incorporated herein by reference.
In view of the above, it is an object of the invention to provide an apparatus and method of dynamically modifying both the luminance and contrast of an image as it is displayed on a display unit in response to changing lighting conditions.
SUMMARY OF THE INVENTION
The invention provides an apparatus and method for dynamically modifying both the luminance and contrast of an image as it is displayed on a display unit in response to changing lighting conditions. Sensors are utilized to continually measure the luminance of the light illuminating the display unit and/or the display surround luminance. Measurement signals generated by the light sensors are processed to provide display luminance and contrast adjustment control signals that gradually cause the adjustment of the display unit's luminance and contrast in response thereto.
More specifically, an apparatus for automatically controlling a display luminance and contrast of a display device is provided that includes an illumination measuring mechanism for measuring a display illumination of a display device; a surround luminance measuring mechanism for measuring a surround luminance of the display device; a calculating mechanism for calculating a current display luminance and a current contrast setting for the display device; a determining mechanism for determining a change in the display illumination and a change in the surround luminance based on measurements performed by the illumination measuring mechanism and the surround luminance measuring mechanism, respectively, a luminance adjustment mechanism for calculating an updated display luminance when the determining mechanism determines a change in the display illumination has occurred, and for adjusting the display luminance of the display device based on the updated displ
Miller Michael E.
Niederbaumer James R.
Bella Matthew C.
Blackman Anthony
Eastman Kodak Company
Novais David A.
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