Television – Video display – Color sequential
Reexamination Certificate
2000-03-03
2001-08-14
Eisenzopf, Reinhard J. (Department: 2614)
Television
Video display
Color sequential
C348S742000, C348S771000
Reexamination Certificate
active
06275271
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a tone display method that overlaps and displays multiple subfields obtained by weighting dynamic images having tones in the time domain in a DLP (digital light processing) image display device using one reflection-type device or other image display device that displays color images by the time-division output of color signals.
2. Brief Description of the Prior Art
In an image display device using the digital display method, such as a veneer DLP image display device using one reflection-type device, a method such as disclosed in U.S. Pat. No. 5,448,314 can be used to display color signals.
FIG. 7
shows an example of the configuration of an image display device.
FIG. 8
shows an example of the configuration of the color wheel (
2
) shown in FIG.
7
. Color wheel (
2
) consists of color filters of green G, red R and blue B with each central angle set at 60°. In order to reduce color separation, the color wheel can be set to have, for example, three rotations for one field.
In
FIG. 7
, 8-bit digital color signals of RGB are input to time division multiplex circuit (
5
). Each of the input color signals of RGB is time-.base compressed to the ⅓ period, time-division multiplexed, and output.
FIG. 9
shows the pattern obtained by time-division multiplexing the period of one field. A DMD (digital micromirror device) (
3
) is controlled by the output signal. Also, the white light emitted from lamp (
1
) used as the light source reaches the DMD (
3
) after passing through color wheel (
2
) used as the color extraction device. In this case, the light of colors G, R, B, corresponding to the periods shown in FIG.
9
and obtained after the white light is transmitted through the color wheel (
2
) and reaches DMD (
3
). In
FIG. 9
, the periods divided corresponding to the colors G, R, B are referred to as segments. In the following explanation and figures, the segments corresponding to colors G, R, B are represented by s, which means segment, and a number counted from the head or start of one field. In this case, color wheel (
2
) rotates clockwise with the light emitted from lamp (
1
) set at the position of 0° (
12
o'clock). The light in colors G, R, B is reflected by DMD (
3
) controlled by the corresponding periods and signals of G, R, B. The output optical signals of G, R, B are irradiated sequentially on screen (
4
) and are sensed as color images.
Each segment of the signals of G, R, B consists of multiple time-base divided subfields used for tone display. As an example of the subfield period, the subfield configuration of the first segment of G in the case of displaying 8 bits, that is 256 tones, is shown in the low-order portion of FIG.
9
.
FIG. 10
shows the subfield configurations of the other segments of G.
FIG. 10
only shows the case of G. However, the patterns are the same for R and B. Reference is made to the tone display method disclosed in Japanese patent application to Kokai, No. Hei 9 [1997]-34399, etc., for the subfield configuration disclosed in this example.
In
FIG. 10
, the portion encircled by a rectangle is a subfield, and the length of the rectangle is the subfield period (time length of the subfield). In the following explanation and figures, the nth subfield is represented by SFn. The time length of each subfield is defined as the weight corresponding to the brightness of one color when only the segment concerned is turned on. In the case of the configuration shown in
FIG. 7
, the weight corresponds to the time when the mirror of DMD is on (lit) or to the number of lighting pulses during the time length. In the following figures, the value of the weight will be displayed below the rectangle that represents each subfield.
The process of selecting the appropriate subfield to be turned on (to be lit up) corresponding to the tone to be displayed will now be explained.
In a conventional example, one field is divided into 34 subfields for one color. Among the 8 bits, the 5 high-order bits are displayed by continuous time-width modulation using 31 subfields, that is, subfields SF
4
-SF
34
having a weight of “8”. The 3 low-order bits are displayed on the binary base using 3 subfelds SF
1
-SF
3
having weights of “1”, “2” and “4”, respectively. In other words, for the subfields used to display the 5 high-order bits, whenever the tone is increased by 8, that is, whenever the 5 high-order bits have a carry of one, the number of lit subfields is increased one at a time in the sequence from SF
4
-SF
34
. Each pixel can display the tones by lighting up the subfields as described above. Since the line of vision is almost fixed on a stationary image, the image quality will not deteriorate by adding subfields for each pixel.
In the aforementioned conventional tone display method using subfields, pseudocontour noise is observed for dynamic images which deteriorates the image quality. Occurrence of pseudocontour of dynamic images is described in the reference (“Studies on Improving Dynamic Image Quality of PDP in Subfield Display” (Japanese Title), which is synonymous with “Consideration on Improving Motion Picture Quality of PDP with use of a Sub-Field Method” (English Title), IEICEJ Technical Report, EID 97-54 (1997-10), pp.
43
-
48
). Since the line of vision moves following the track of a dynamic image, pseudocontour occurs because the position where the eyes process time integration changes in the space following the movement of the line of vision. In other words, when the line of vision moves at a speed to cover multiple pixels during the display period of one field, subfields are added not only in one pixel but over multiple pixels. As a result, the original image cannot be obtained, and the image quality is deteriorated.
FIG. 12
is a diagram explaining a tone display method, which displays 256 tones using n subfields. In this case, the aforementioned problem becomes extremely serious. Pixels A and B are arranged adjacent to each other. Pixel A displays 127 tones with subfields SF
1
-SFm (m=n/2) turned on and subfields SF (m+1)-SFn turned off. Pixel B displays 128 tones with subfields SF
1
-SFM turned off and subfields SF (m+1)-SFn turned on. In
FIG. 12
, the pixels are arranged in the vertical direction, while the subfields are arranged in the horizontal direction. In other words, the vertical direction in
FIG. 12
indicates the spatial movement of the vision spot, while the horizontal direction indicates the time movement of the vision spot. In this case, when the vision spot does not move from pixel A (arrow c), the integral value of one field of pixel A becomes 127 tones as displayed. However, when the vision spot moves from pixel A to pixel B at a speed of 2 pixels per field (arrow a), both of the integral values of pixels A and B become 255 tones. When the vision spot moves from pixel B to pixel A at a speed of 2 pixels per field (arrow b), both of the integral values of pixels A and B become 0 tone.
In order to measure the actual image quality deterioration in a quantitative manner,
FIG. 11
shows a computer-simulated image observed when a moving lamp waveform is displayed using the tone display method with the subfield configuration shown in FIG.
10
. The basic method of the simulation is described in the above-mentioned reference. In this example, subfields are divided into 6 segments. Each unit period of each subfield is appropriately set corresponding to the position in accordance with the aforementioned division in one field. In this simulation, the time integral level of the eyes is calculated when the vision spot moves to the right at a speed of 8 pixels during the display period of each field. In this case, the simulation results are for G. However, the same results can be obtained for R and B. In the following, the case of G will be explained as an example.
For the lamp waveform used in this case, the level (tone) moves up by one corresponding to a movement of one pixel to the right in the horizontal direction. Levels 0-255
Hitomi Hisakazu
Kunzman Adam J.
Ohmae Hideki
Brady III Wade James
Brill Charles A.
Eisenzopf Reinhard J.
Matsushita Electric - Industrial Co., Ltd.
Telecky , Jr. Frederick J.
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