JP3790277B2 - Pulse width modulation digital display pixel intensity adjustment method and display system to which this method is applied - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to the field of visual display systems, and more particularly to digital pulse width modulation display systems.
[0002]
[Prior art]
The display system has long had the ability for viewers to adjust display characteristics to adapt to ambient conditions, adjust for low quality input signals, compensate for aging display devices, and adapt to personal preferences. Have given. Two of the main means for adjustment have been brightness control and contrast control.
[0003]
Brightness control theoretically adjusts the brightness or intensity of the display by changing the amount of light emitted, reflected, or transmitted by the display. Contrast control adjusts the brightness ratio between the bright and dark areas of the screen. Typically, both brightness adjustment and contrast adjustment are realized by changing either the gain characteristic or the offset characteristic to the image signal path, or by changing both the gain characteristic and the offset characteristic.
[0004]
[Problems to be solved by the invention]
It can be said that it is difficult to realize brightness control and contrast control in an all-digital image display system. Typically this involves additional hardware such as a multiplier or look-up table that scales the image data. Software is also used to scale the image data, but this does not require additional processing power.
[0005]
[Means for solving the problems]
A method of adjusting the intensity of a pulse width modulated digital display pixel is disclosed, wherein each pixel is represented by an intensity word and is displayed sequentially for a duration that depends on the weight of that bit. According to one embodiment of the disclosed invention, the display duration of each bit of an intensity word results in a pixel that increases the pixel's duty cycle or increases the pixel's duty cycle or decreases the pixel's duty cycle. Changed to either reduce the brightness. In order to adjust the contrast ratio of the digital display, the duration of some bits is increased while the duration of other bits is reduced. The disclosed method and system have the advantage of being economically and easily implemented.
[0006]
【Example】
The invention taught herein may be applied to any display system that uses pulse width modulation to control image intensity. For illustrative purposes, the following discussion will focus on a digital micromirror device (hereinafter referred to as DMD) spatial light modulator (hereinafter referred to as SLM). DMD can be realized in several types, such as cantilevered beam, flexure beam, and torsion beam. The present disclosure will concentrate on US Pat. No. 5,061,049, “Spatial Light Modulator and Method,” accepted by Texas Instruments. Other display devices could be used including liquid crystal device (hereinafter referred to as LCD) arrays and light emitting device (hereinafter referred to as LEDs) arrays.
[0007]
Each element of the digital display can only produce two intensity levels: on and off. Pulse width modulation is used to generate other levels of brightness. Pulse width modulation changes the duty cycle of each pixel according to the desired intensity of the pixel. This appears to be a different intensity level as the viewer's eyes integrate the light from each pixel over time providing a different duty cycle. In a pulse width modulation display system, the duty cycle for each pixel is specified as an n-bit word. The significant digit of each bit determines how long that bit is displayed. For example, bit n is displayed twice as long as bit n-1. The length of time for which a given bit is displayed is determined by the weight value of that bit, the frame period, and the maximum duty cycle. Typically, all bits of one weight value are displayed simultaneously, followed by all bits of the next weight value.
[0008]
FIG. 1 shows a typical time line during one frame of a 5-bit digital pulse width modulation display system. In FIG. 1, the horizontal axis represents time and the vertical axis represents pixel intensity, ie either on or off. According to the 5-bit system, 32 unique intensities can be displayed. For the described embodiment, the selection of the 5-bit data word is arbitrary and has been selected for illustration purposes. The present invention can be implemented with any size data word having at least 2 bits. Typically, 8-bit data is used for each color displayed.
[0009]
Frame period 30 is the time interval required to load and display one 5-bit word of data on a DMD-based display system. The bit period 32 is the least significant bit (hereinafter referred to as LSB), that is, the display period for bit 0 (hereinafter referred to as LSB period), and the bit period 34 is the most significant bit (hereinafter referred to as MSB), that is, This is a display period for bit 4 (hereinafter referred to as an MSB period). Through FIGS. 1-5, the pixel is turned on for each bit period, but this is done for illustration purposes, and each bit period may be turned on or off independently of any other bit period. Since each element of the DMD includes a memory cell, the DMD can be loaded with one bit while the other bits are displayed. This increases the maximum duty cycle of the DMD base display and reduces the bandwidth requirements of the DMD interface. A blanking period is used when the display period for a bit is shorter than the time required to load the array. During the blanking period, each pixel is turned off, during which data for the next weight value is written to the array. DMD arrays are typically designed to quickly set or clear a large group of mirrors by writing a single data word to the array. This operation is called a block set or block clear.
[0010]
FIG. 1 shows two blanking periods 36 and 38 during which the pixel is turned off. The duration of these periods is typically equal to the time required to load a frame of data into the display, but may not be required in all display systems. Other display systems may have more blanking periods for each pixel. For example, in LCD and LED systems, data is scanned into the display from row to row, one bit at a time. In this case, each pixel is turned off during each bit period, while the remaining rows of the display are driven.
[0011]
The maximum brightness of the image is determined by how much light can be emitted, reflected, or transmitted by the display device within a given interval of time. The brightness may be increased by increasing the pixel duty cycle. The prior art relies on scaling the image data word, thereby changing the value of the data word. Means for scaling the data, such as multipliers or look-up tables, are usually required by prior art solutions. The present invention discloses a method for changing the display brightness without requiring scale conversion of image data. The disclosed method relies on changing the duty cycle for a pixel without changing the data word. One implementation is to extend the bit period for each displayed bit. However, display systems are typically designed to maximize the duty cycle of full-scale data, and the bit period cannot be further extended without reducing the frame rate.
[0012]
The blanking period limits the duty cycle of each pixel in the display, thus reducing the maximum luminance capability of the display. According to one embodiment of the present invention, the display brightness can be increased by changing one or more of the block clear periods to block set periods. FIG. 2 shows a typical 5-bit display timeline with increased brightness according to a first embodiment of the present invention. As shown, one block clear period 40 is now one block set period. If even greater brightness is required, the second block clear period 38 could be changed to a block set period. This method of increasing the brightness of the display has the disadvantage that it results in a slightly larger step increase in brightness, which is not related to the desired brightness. To offset this large step increase, the weighted bit period can be shortened at the same time to achieve a more gradual increase in brightness. The taught method may also reduce the contrast ratio of the display. In a color system, changing a block reset to a block set may have a tendency to wash out the true color of the image. However, despite these drawbacks, there are applications where increased brightness is desirable for the viewer, even if certain artifacts are introduced.
[0013]
In order to reduce the brightness of the image, the display period for one or more bits may be shortened. FIG. 3 shows an exemplary 5-bit timeline according to a second embodiment of the invention in which the display period for each bit is shortened by an amount equal to 1/2 of the LSB. Note that in FIG. 3, the block clear period 48 is now longer than the time required to load the display. Although FIG. 3 shows each bit shortened by the same amount, similar effects can be achieved by applying different shortenings to each bit. For example, in some applications, only the LSB period will be shortened. Other applications may shorten each period by a different amount. One method is to proportionally shorten each period in order to maintain a relative decrease in each weight. If the bit period is shortened to be shorter than the SLM response time, the bit is not displayed. Depending on the method used to shorten these periods, artifacts may be created.
[0014]
Examples up to this point have focused on display systems with single intensity words, such as monochrome displays. The invention could also be applied to a system having at least two data words, such as a color system having a separate data word for each color. When applied to a color system, the handling of data words may be done equally for each color word, or a certain number of colors may be handled differently to change the tone of the displayed image.
[0015]
Another display characteristic that can be controlled using the present invention is the contrast ratio. In order to change the contrast ratio, certain bit periods are expanded while other certain bit periods are shortened. If the viewer wants to increase the contrast, the period of one or more upper bits containing the MSB is extended, while the period of one or more lower bits containing the LSB is shortened. This results in both increasing the brightness of bright pixels and decreasing the brightness of low intensity pixels. For example, if the MSB period is extended , the brighter half of all intensity words will increase brightness. If the LSB period is shortened, the remaining half of the intensity words will reduce the brightness. The decrease in the thinnest value will be most noticeable.
[0016]
FIG. 4 shows a 5-bit time line for a system with increased contrast according to a third embodiment of the present invention. In FIG. 4, the MSB period 50 is extended, while the two lower bit periods 52 and 54 including the LSB are shortened. One alternative embodiment would simply be to shorten the duration of one or more lower bits that contain the LSB . The MSB period could not be extended without reducing the LSB period unless the system was designed to include a special blanking time within each frame.
[0017]
The opposite is done to reduce the contrast ratio. While the MSB period is shortened , the LSB period is extended . This reduces the brightness of the brightest pixel and increases the brightness of the thinnest pixel. In order to achieve the same effect, the MSB period may be shortened without extending the LSB period. FIG. 5 shows a timeline for a system with a reduced contrast ratio according to a fourth embodiment of the present invention. In FIG. 5, the MSB period 56 is shortened while the LSB period 58 is extended.
[0018]
In the previous discussion, the viewer adjusted the brightness, tint, and contrast of the image. One alternative embodiment allows the display system to automatically adjust the image. FIG. 6 shows a display system 60 that is adjusted by either the viewer or the system controller 62. The viewer adjusts the image using brightness control 64, tint control 66, and contrast control 68. The system can determine when image characteristics should be adjusted, either by monitoring the image with the image sensor 70 or by processing the input data stream 72. Color and contrast information may also be obtained and provided for return to the system controller. Image sensor 70 may also be used to monitor ambient light to assist in determining the proper brightness level.
[0019]
Thus, although specific embodiments for brightness and contrast control for digital pulse width modulation display systems have been disclosed so far, such specific citations are set forth in the appended claims. It is not intended to be considered a limitation on the scope of the invention except insofar as possible. Furthermore, although the present invention has been described with reference to certain specific embodiments thereof, it should be understood that other such variations will now be presented to those skilled in the art, and all such variations are described above. It is intended to be encompassed by the claims.
[0020]
The following items are further disclosed with respect to the above description.
[0021]
(1) A method of adjusting the intensity of a pulse width modulated digital display pixel,
Representing each pixel with an intensity word having at least 2 bits;
Sequentially displaying the at least two bits, wherein each of the bits is displayed for a duration that represents a weight of the bit;
Changing the display duration of the pixel.
[0022]
(2) A method according to claim 1, wherein the display duration is shortened, thereby reducing the brightness of the pixels.
[0023]
(3) The method according to claim 1, wherein the display duration for all bits is changed.
[0024]
(4) The method of claim 1, wherein the display duration for all the bits is changed equally.
[0025]
(5) The method according to claim 1, wherein the display duration for two or more of the bits is changed proportionally.
[0026]
(6) The method of claim 1, wherein the pixel sequentially displays at least two color intensity words, and the changing step is performed equally for each of the color intensity words.
[0027]
(7) The method of claim 1, wherein the pixel sequentially displays at least two color intensity words, and the changing step is performed differently for each of the intensity words.
[0028]
(8) The method according to claim 1, wherein the pixel has a blanking period during a display period, and the pixel is turned on during the blanking period.
[0029]
(9) The method of claim 1, wherein the display duration of at least one of the most significant bits is extended, thereby increasing the contrast ratio.
[0030]
10. The method of claim 1, wherein the display duration of at least one of the least significant bits is reduced, thereby increasing the contrast ratio.
[0031]
11. The method of claim 1, wherein the display duration of at least one of the most significant bits is shortened, thereby reducing the contrast ratio.
[0032]
12. The method of claim 1, wherein the display duration of at least one of the least significant bits is extended, thereby reducing the contrast ratio.
[0033]
(13) The method of claim 1, wherein the display duration of at least one of the most significant bits is extended and the display duration of at least one of the least significant bits is reduced, thereby increasing the contrast ratio. ,Method.
[0034]
(14) The method of claim 1, wherein the display duration of at least one of the most significant bits is reduced and the display duration of at least one of the least significant bits is extended, thereby reducing the contrast ratio. Decrease the way.
[0035]
(15) Input image data stream consisting of data words,
A digital display device for receiving the image data stream and displaying an image representing the data word;
At least one input image modulation signal;
A digital display system including a display system controller that changes a display duration of the bits based on the image modulation signal.
[0036]
(16) The system according to item 15, wherein the image modulation signal determines a luminance of the image representing the data word.
[0037]
(17) The system according to item 15, wherein the image modulation signal determines a color tint of the image representing the data word.
[0038]
(18) The system according to item 15, wherein the image modulation signal determines a contrast ratio of the image representing the data word.
[0039]
(19) The system according to item 15, wherein the image modulation signal is generated by a viewer.
[0040]
(20) The system according to item 15, wherein the image modulation signal is generated by an image sensor.
[0041]
(21) A method and system for adjusting the brightness and contrast of a digital pulse modulated display without scaling the input image data is disclosed. The brightness is adjusted by changing the duty cycle of the display pixel, either by changing the bit display duration or by turning on the pixel during the blanking period. The contrast ratio may be changed by changing at least one display duration of the upper bits including the MSB to be different from at least one display duration of the lower bits including the LSB . Contrast may be increased by extending MSB display duration 50 and shortening LSB display duration 52. Contrast may be reduced by reducing the MSB display duration 56 and extending the LSB display duration 58. The color tint of the display image may be changed by individually changing the brightness of the constituent colors.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a time line for a typical 5-bit digital display using pulse width modulation.
FIG. 2 is a diagram illustrating an example of a time line for a typical 5-bit digital display with increased brightness according to a first embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of a time line for a typical 5-bit digital display with reduced luminance according to a second embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of a time line for a typical 5-bit digital display with increased contrast according to a third embodiment of the present invention.
FIG. 5 is a diagram illustrating an example of a time line for a typical 5-bit digital display with reduced contrast according to a fourth embodiment of the present invention.
FIG. 6 is a schematic view of a display system according to the present invention.
[Explanation of symbols]
30 frame period 32 LSB period 34 MSB period 36, 38 Return blanking period 40, 48 Block clear period 50 MSB period 52, 54 LSB period 56 MSB period 58 LSB period 60 Display system 62 System controller 64 Brightness control 66 Light color control 68 Contrast Control 70 Image sensor 72 Input data flow

Claims (2)

A method of operating a pulse width modulated digital display comprising :
Assigning a portion of a display period to each bit in a binary luminance word, which is a binary word representing luminance, such that the duration of each display period portion corresponds to the binary weight of the bits;
Receiving a binary luminance word having at least 2 bits;
Displaying for a period of time assigned to bits in the received binary luminance word ;
Repeating the receiving step and the displaying step until a contrast adjustment signal is received;
Responsive to the contrast adjustment signal, lengthening a display period portion assigned to at least one bit and shortening a display period portion assigned to at least one other bit;
Adopting the display period portion whose length has been changed, repeating the receiving step and the displaying step;
Including a method. A digital display system,
A digital display device that receives binary weighted data words and displays an image represented by the binary weighted data words, wherein the display period for each data word is 2 for each data word. A digital display device determined by a bit display period corresponding to a hexadecimal bit ;
A display system controller for receiving a contrast correction signal, increasing at least one bit display period in response to the contrast correction signal, and shortening at least one bit display period ;
Including digital display system.

Images