Optics: image projectors – Color filter
Reexamination Certificate
2002-09-24
2004-11-30
Dowling, William C. (Department: 2851)
Optics: image projectors
Color filter
C353S121000, C353S122000
Reexamination Certificate
active
06824276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an image processing technique depending on changes of an optical system of a projector.
2. Description of Related Art
Projectors can be broadly classified into two categories: data projectors and video projectors, depending on their intended use. Classifying projectors therefore requires definite performance.
Data projectors project an image based on image signals received from an information terminal, such as a personal computer. Data projectors are typically used for presentations in well-lighted places, such as conference rooms and lecture halls, where brightness is important for a projected image. On the other hand, video projectors project a screen image of TV or a movie based on screen image signals received from an AV device. Video projectors are typically used for watching a movie in dark places, such as less-illuminated rooms, where picture quality including color balance or contrast is more important than brightness.
Various types of discharge lamps, such as ultra-high pressure mercury lamps, metal halide lamps and xenon lamps are generally used to provide illumination for projectors in terms of keeping high color rendering properties and high luminance.
FIG. 10
is a graph that shows an emission spectrum of an ultra-high pressure mercury lamp. Projectors divide illumination into three colors; red light (R), green light (G) and blue light (B), which are modulated by light valves respectively, thereby projecting an image. Illumination can be utilized when it is divided into, for example, blue light in 400-500 (nm) wavelength range, green light in 500-600 wavelength range and red light in 600-700 wavelength range.
Projectors can be generally used as data projectors. Illumination that includes green light with high visibility can be used to enhance brightness of the projected image, which loses color balance between R, G and B.
Color balance adjustment in a projector that is used as a video projector can be performed by setting the tone value of the image data with regard to green light to, for instance, 0.8 times stronger than that used for a data projector. Namely, color adjustment can be achieved by weakening the strength of green light due to the drive of a liquid crystal panel (hereafter “LCP”), as shown in a dashed line in FIG.
10
.
However, projectors that use an LCP as a light valve have not sufficiently attained a high level contrast ratio for the projected image in terms of the above-mentioned color balance adjustment. The contrast ratio is represented in the ratio between the brightness of the all-white-image and all-black-image.
FIG. 11
is a chart that shows the relationship between an input tone value and the brightness in projecting a gray color image where input tone values of R, G and B are equivalent. A solid line L
1
shows the relationship between the input tone value and the brightness without the above color balance adjustment, and a dashed line L
2
shows this relationship with the color balance adjustment. The contrast ratio without the color balance adjustment is represented by B
1
/B
0
, and B
2
/B
0
represents the contrast ratio with the color adjustment. As shown in
FIG. 11
, in the above-mentioned adjustment, the brightness for an all black image remains in B
0
, though the brightness for an all white image decreases from B
1
to B
2
due to the characteristic of an LCP that luminance barely passes light valves even when all light valves are closed to project all black image (refer to a chain double-dashed line in FIG.
10
). The contrast ratio thus decreases in the above-mentioned adjustment.
SUMMARY OF THE INVENTION
Accordingly, it has been difficult to achieve both the preferable color balance adjustment and the preferable contrast ratio at the same time.
Furthermore, the color balance adjustment has not been efficient for a black or a low tone image. There is a slight difference in the brightness between a black image that is projected with the color balance adjustment and such a projected image without the adjustment. Utilizing a lot of green light illumination has caused black images to be projected in a greenish gray color.
The present invention thus provides a technique of enhancing picture quality of an image projected by a projector.
At least part of the above and the other related advantages are attained by a projector with the following construction. The first embodiment of the projector includes: an image processing module that performs image processing with regard to an input original image data; an image generating module that generates an image based on an image data that is provided with the image processing; a projection optical system that projects an image generated by the image generating module using illumination light that includes specific emission spectrum; and an optical filter that is detachable and weakens at least part of spectral intensity in a wavelength range among an emission spectrum included in the illumination light, which affects the projection of the image. The image processing module performs the specific image processing in response to the changes of the spectral intensity caused by putting on/taking off the optical filter.
As described above, the color balance adjustment for a projected image is performed through the process of image processing in a projector that uses an LCP as a light valve, which causes low contrast ratio. The projector of the present invention has a detachable optical filter in order to weaken at least part of the spectral intensity. Using such an optical filter enables color balance adjustment for the projected image, and reduces or prevents low contrast ratio because that reduces the brightness for black color in the projected image as well as other colors. The optical filter can be removed from a projection optical system when brightness is more important than color balance.
In the projector of the present invention, because spectral intensity in projection light, which affects projection of the image, is different when the optical filter is attached compared to when it is not attached, the color balance of the projected image is different when the optical filter is attached compared to when it is not attached. The image processing module in the projector enables the adequate image processing, with regard to the original image data in response to the changes of spectral intensity in projection light, depending on the optical filter status, whether attached or not, thereby achieving both preferable color balance and preferable contrast ratio at the same time and enhancing picture quality of the projected image.
In the first embodiment of the present invention, the image processing may be any of diverse image processing techniques. It is, however, preferable that the specific image processing is color adjustment.
This procedure desirably enhances color reproducibility in the projected image.
In the first embodiment of the projector, it is preferable that the wavelength range affecting projection of the image responds to red light, green light and blue light, and that the optical filter has the highest reducing rate of spectral intensity in the wavelength range corresponding to green light.
Hereinafter, ‘reducing rate of spectral intensity in wavelength range corresponding to green light is the highest’ indicates that reducing rate of spectrum strength in wavelength range corresponding to green light is the highest among the projected light emitted from the projection optical system, which is not caused by characteristics of the optical filter.
In general, illumination light from a projector that uses an LCP as a light valve becomes greenish. Reducing spectral intensity with regard to green light enables effective color balance adjustment with high contrast ratio, and reduces or prevents the projected images in black or low scale from being greenish.
In the first embodiment of the present invention, the image processing module includes: a memory module that stores parameters used for the image process
Dowling William C.
Oliff & Berridg,e PLC
Seiko Epson Corporation
LandOfFree
Image processing with changes of optical system of projector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image processing with changes of optical system of projector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image processing with changes of optical system of projector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3350444