JP2005196169A - Calibration method for calibrating fixed format emissive display device, and fixed format emissive display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a calibration method for calibrating a fixed format emissive display device having a plurality of pixels and a fixed format emissive display device. <P>SOLUTION: The display device have pixels each including at least three sub-pixels for emitting lights of the different real primary colors. The calibration method includes the steps of: determining, for each real primary color separately, color coordinates of virtual target primary colors which can be reached by at least ≥80% of the pixels of the display device; determining color gamut defined by the determined virtual target primary colors; and adjusting drive currents to sub-pixels so that pixels which can not reached by the virtual target primary colors can have colors in the determined color gamuts. Further, display having an extended range of colors i.e. a gamut of colors that is more than the gamut provided by an electronic multicolor display based on n virtual primary color, for example, measured on a chromaticity diagram is represented. Consequently, an image having uniform colors and/or lightness can be generated by using this fixed format emissive display device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to light emitting display devices, and more particularly to fixed format light emitting display devices such as flat panel displays, and more particularly to a method and apparatus for color correction of such display devices.

BACKGROUND OF THE INVENTION Electronic display devices can generate images or light using transmissive or emissive materials. The emissive material is usually a phosphorescent or electroluminescent material. By way of example, thin film and thick film electroluminescent display devices (EL display devices such as thin film TFEL display devices such as those manufactured by Sharp, Planar, LightArray or iFire / Westaim) Inorganic electroluminescent materials such as those used in the above. Another group is organic electroluminescent materials (such as organic light emitting diode (OLED) materials), which are deposited in layers containing small molecule or polymer technology, or phosphorescent OLEDs, where the electroluminescent material is It is applied with a phosphorescent material. Yet another group of materials are phosphors commonly used in fixed cathode ray tubes (CRT) or plasma display devices (PDP) and also in emerging technologies such as laser diode projection display devices, in this case A phosphor embedded in the projection screen is excited using a laser beam.

There are two basic types of displays: a fixed format display that includes a matrix or array of “cells” or “pixels”, each generating or controlling light in a small area, and no such fixed format There are displays, for example CRT displays. For fixed formats, there is a relationship between the pixels of the displayed image and the display cells. Usually this is a one-to-one relationship. Each cell can be addressed and driven separately. Direct-view display devices such as light emitting fixed formats, especially light emitting diode (LED), field emission (FED), plasma, EL, OLED and polymer light emitting diode (PLED) display devices are too large for conventional CRT display devices. And / or used in heavy situations and provided as an alternative to non-light emitting display devices such as liquid crystal display devices (LCDs). Fixed format means that the display device includes an array of individually addressable light emitting cells or pixel structures rather than using a scanning electron beam as in a CRT. Fixed format relates to pixelation of the display and the fact that individual parts of the image signal are assigned to specific pixels in the display device. Even with a color CRT, the phosphor trio of the screen shows no pixels. That is, no requirement or mechanism is given to ensure that the sample in the image aligns with it in any way. The term “fixed format” does not relate to whether the display device can be expanded into a larger array, for example by tiling. A fixed format display device may include an assembly of pixel arrays, for example, this may be a tiled display device, and may itself include modules that constitute a tile array tiled into a super module. Absent. Thus, “fixed format” does not relate to the fixed size of the array, but to the fact that the display device has a set of addressable pixels in the array or group of arrays. It is difficult to manufacture a very large fixed format display device as a single device manufactured on a single substrate. To solve this problem, multiple display devices or “tiles” can be placed adjacent to each other to form a large display, ie, an array of multiple display elements placed physically next to each other, Make it visible as a single image. By transferring the image data to various display devices by packetized data transmission, it is very easy to separate the displayed image into tiles.

  In creating a color display, the color is obtained by mixing light from primary colors such as, but not limited to, red (R), green (G) and blue (B). For fixed format light emitting display devices, separate or primary individual “primary” emitter layers produce these colors. If primary color emitter layers are given adjacent to each other and usually close to each other, from some minimum distance (composite distance), the observer cannot distinguish the primary color emitters and the resulting single blend I can only see the color. Most color representations are two-color or full-color, each representing two primary colors or at least three primary color emitters per pixel.

  In order to produce as many colors as possible, including white, at least three primary emitters are required with each emitted wavelength as close as possible to pure colors, such as pure red, pure green and pure blue. The color vision theory is described in, for example, 2002, R.A. L. It is well known from the book “Display Interface” by Myers and Wiley. Primary colors exist only as mathematical structures, which are outside the real world color range. More practical color spaces and color coordinate systems, such as the CIE chromaticity table, have been standardized. Fixed format display devices typically use red, green and blue pixel elements, which are typically referred to as RGB pixel elements. A CIE chromaticity table showing the location of typical OLED and LED materials (graphs 10 and 11, respectively) is shown in FIG. The position of this table is for a typical OLED display (graph 10), ie, red, RO, green, GO and blue, BO, and for an LED display (graph 11), ie red, RL, green, GL, Indicated in blue and BL.

  Finally, fixed format display emitters have a certain emission spectrum. Each material also has a different dominant wavelength. This unambiguously determines which colors can be generated in the pixel.

  As can be seen in FIG. 1, it can be seen that multiple LEDs and multiple OLEDs exhibit variation in the emission spectrum (eg, due to variations in the production process). Because the human eye is very sensitive to color differences, color changes between many pixels can be perceived, creating “fixed pattern noise” or distracting artifacts known as dithering. Absent.

  In addition, during the process of aging differences, individual subpixels may vary in luminous efficiency and / or color. Color and / or emission differences are more perceptible over time if the luminous efficiency and / or color of the subpixel changes during aging and not all subpixels age in substantially the same way It may become something.

US-2003 / 0443088 describes a solution to the above problem. For a given display device, the color of each subpixel is characterized as part of the final inspection prior to shipment at the factory. The color represented for each pixel is set to the minimum color gamut for the complete population of pixels. That is, the color emanating from each pixel is limited to the smallest color gamut that all of the pixels in the display device can achieve.
US-2003 / 0443088

  This approach assumes that the color exhibited by all of the pixels of the display device is substantially uniform. However, this sacrifices the potential color gamut that is possible with a given display.

SUMMARY OF THE INVENTION An object of the present invention is to extend the potential color gamut that substantially all pixels of a fixed format light emitting display can handle. Preferably, an image with uniform color and / or brightness is generated by a fixed format light emitting display.

  In this connection, the color range refers to a color gamut that can be displayed on an electronic multicolor light emitting display device, and this electronic multicolor light emitting display device uses n ( n incorporates 3 or more (n> = 3) virtual primaries. The extended color range refers to a color gamut that is higher than the color gamut of an electronic multicolor display device based on n virtual primaries as measured, for example, in a chromaticity table.

  The above objective is accomplished by a method and device according to the present invention.

One aspect of the present invention provides a calibration method for calibrating a fixed format light emitting display device having a plurality of pixels, each pixel having at least three subpixels for emitting light of different real primary colors. This method includes
Determining for each real primary color separately the color coordinates of the virtual target primary color that can be reached by at least 80% of the pixels of the display device;
Determining a color gamut defined by the determined virtual target primary color;
Adjusting a drive current to the sub-pixel to achieve a color within the determined color gamut for pixels that cannot reach the virtual target primary color. Any color in the color field can be at least one virtual primary, or a combination of two or more of at least one virtual primary and any real primary, such as at least one virtual primary and any real primary Can be reached by a linear combination of two or more of the primary colors. The present invention includes within its scope the ability to change the target virtual primary color during the lifetime of the display device. This may be necessary, for example, if the actual primary color has changed due to (different) aging or other environmental effects.

  In the method according to the invention, the step of determining the color coordinates of the virtual target primary color comprises the step of determining the centroid of the cloud formed by the corresponding real primary color coordinates of all the pixels of the display device. Including. The color coordinate values determined for the virtual target primaries may differ by up to 20% from the respective values of the cloud center of gravity color coordinates. The method may further include determining a gravitational line of the cloud formed by the color coordinates of the actual primary colors of all pixels of the display device corresponding to the determined virtual target primary color.

  The color coordinates of the virtual target primary color are selected on the gravity line, within the deviation from the gravity line or by the distance from the gravity line, and the color coordinate value of the virtual target primary color is the color coordinate value of the point located on the gravity line From up to 20% at most.

The target brightness of each target virtual primary color is preferably such that all or substantially all (eg 80% or more) real primary colors can achieve the target brightness corresponding to the virtual primary color. To be determined. The drive current to the subpixel is adjusted to achieve the target brightness. The determination of the target luminance of the virtual target primary color may depend on the application in which the display device is used. The target brightness of the virtual target primary color may be selected to give improved brightness uniformity or a high absolute brightness value. The determination of the target luminance of the virtual target primary color can be made after the virtual target primary color is initially determined. This means that the calibration process that may be required for aging in the application of the display used is repeated. Instead, the virtual target primary color can be determined a second time when the display application is changed, and is therefore independent of sub-pixel aging. This should be considered that the display has multiple display modes. Depending on the application, different display modes may be selected, each display mode corresponding to a specific selection of virtual target primaries.

  The method may include determining a virtual target primary color that can be achieved by all subpixels of the display device. The method may also include determining a color gamut that can be achieved by all subpixels of the display device.

  Typically, a color gamut is formed using a plurality of linear combinations of virtual target primaries.

  The determination of the color coordinates of a separate virtual target primary color for each primary color may depend on the application in which the display device is used. In some applications, color saturation may be more important, but in other applications, color uniformity may be more important. Both can correspond to different virtual target primaries. The virtual target primaries may be determined to give better results in terms of color saturation than in terms of color uniformity. The virtual target primaries may be determined to give better results for color uniformity than for color saturation.

  The correction method can be used, for example, to compensate for the effects of aging, or to switch to another mode of the display device, for example when color uniformity is more important than color saturation or vice versa. Can be repeated after at least once.

  The number of virtual target primaries may be equal to the number of actual primaries.

  Adjusting the drive current to the sub-pixel to achieve a color within the determined color gamut includes at least a positive drive stimulus value as well as a first real primary color having a negative drive stimulus value. It may also include adjusting the drive current of one other real primary color. The adjustment of the drive current of the first real primary color and the at least one other primary color can be such that the color achieved within the determined color gamut is projected at right angles in the plane of the stimulus coordinate system. Extends to the stimulus coordinates of two real primary colors that have no negative drive stimulus.

  In yet another aspect, the present invention provides a fixed format light emitting display having a plurality of pixels, each pixel including at least three sub-pixels for emitting light of different real primary colors. The display device determines at least 80% of the pixels of the display device separately for each real primary color by determining the centroid of the cloud formed by the color coordinates of the corresponding real primary color of all pixels of the display device. Means for determining the color coordinates of a virtual target primary color that can be reached, means for determining the color gamut defined by the determined virtual target primary color, and for pixels that cannot reach the virtual target primary color Means for adjusting the drive current to the sub-pixel to achieve a color within the specified color gamut.

  These and other features, features and advantages of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

  In the different drawings, the same reference signs refer to the same or analogous elements.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The present invention will be described with respect to particular embodiments and with reference to certain drawings but is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

  Although the present invention will be described with reference to OLED display devices, particularly tiled OLED display devices, the present invention is not limited to tiled OLED display devices, but is tiled or monolithic. It can be used with any light emitting display device.

  Hereinafter, the light-emitting pixel structure refers to a light-emitting fixed format pixel that may include a plurality of pixel elements, for example, red, green, and blue pixel elements. Each pixel element or color element may itself consist of one or more sub-elements. Thus, the pixel structure can include sub-pixel elements. The pixel structure may be monochromatic or colored. Furthermore, the array may be a passive or active matrix.

  Further, the terms first, second, third, etc. in the description and claims are used to distinguish similar elements and are not necessarily used to indicate a sequential or chronological order. I can't. The terms used in this manner are interchangeable under appropriate circumstances, and the embodiments of the invention described herein may be operated in an order other than those described or shown herein. You should understand what you can do.

  It should be noted that the term “comprising” as used in the claims should not be construed as limited to the means listed below, and does not exclude other elements or steps. Therefore, the scope of the expression “apparatus including means A and B” should not be limited to an apparatus consisting solely of components A and B. This means that the only relevant components of the device are A and B with respect to the present invention.

  For example, a conventional manufacturing method of an OLED display device results in a pixel structure as shown schematically in FIG. 2 with a transparent substrate 2, which is usually a glass substrate and is closest to the viewer. Facing the display direction. Behind this substrate is deposited a series of layers 4 to 8, for example at least a first transparent electrode 4, an organic light emitting element 6 and a second electrode 8. The organic light emitting material is deposited for each color in each pixel structure, for example for the three color elements 6, red, green and blue for each pixel structure. Thus, each pixel structure can emit white light or any color by controlling the light energy emitted from each color element of the pixel structure. Typically, additional layers are deposited, such as the electronic layer 7 and the hole transport layer 5 respectively (adapted from FIGS. 4 to 13 of “Display Interface” by 2002, RL Myers, Wiley). See FIG.

  Each color can be represented by its tristimulus values X, Y, Z in the CIE color space. The Y value indicates the contribution to the perception of the brightness of the human eye, which is called brightness or brightness. The color can also be expressed as Y and the color function x, y, z, where

It is.

  In accordance with the present invention, each pixel is characterized during or after manufacture of the light emitting fixed format display device. This can be done, for example, by measuring the color characteristics and brightness of each pixel separately for driving stimuli to each of the pixel elements, and thus red (R), green (G) and blue for all pixels. This can be done by measuring the components of (B). In this way, the color gamut for each pixel is known. FIG. 3 shows the color gamuts of three separate pixels of a light emitting fixed format table device, for example. For example, the first pixel emits red R1, blue B1, and green G1. The color gamut of the first pixel is indicated by the triangle R1B1G1. The second pixel emits red R2, blue B2, and green G2. The color gamut of the second pixel is indicated by the triangle R2B2G2. The third pixel emits red R3, blue B3 and green G3. The color gamut of the third pixel is indicated by triangle R3B3G3. The color gamuts of these three pixels are drawn in the CIE color space in FIG. The x-axis is CIEx color coordinates, and the y-axis is CIEy color coordinates. In order to make an appropriate calculation, the calculation should be based on tristimulus values X, Y, Z, or based on CIEx, CIEy and Y. That is, it is important to take luminance into consideration. In practice, the display device contains much more than three pixels, and the color gamut of each of these pixels is measured. The same reasoning can be done in different color spaces.

  The color gamut of the entire display is reduced to a color gamut that can be reached by all or substantially all of the pixels of the display device, for example, a color gamut that can be reached by at least 80% of the pixels of the display device. The term “color that a pixel can reach” means that there is a drive current for the pixel element of the pixel so that the pixel elements as a group can emit the specified color. In the example shown in FIG. 3, the point indicated by G represents all pixels by manipulating the sub-pixel combination of pixels, not by manipulating only the green sub-pixel of any pixel. Is the point that gives the most saturated green that can be reached. The point indicated by R gives the most saturated red that all pixels can reach by manipulating that sub-pixel combination, and the point indicated by B manipulates that sub-pixel combination. This gives for each of the pixels the most saturated blue that all pixels can reach. One possible algorithm for calculating the points denoted R, G, B may be to calculate the lines between the color points and the intersection of these lines. However, usually the target color coordinate value is determined, for which all correction factors C are greater than or equal to 0 (see Equation 2 below). Thus, the display color gamut can be reduced to a triangle RBG as described in US-2003 / 0043088. R, G and B are referred to as virtual primaries in the description and claims of the present invention. These are called virtual primaries because they are not real primaries. That is, few components of two or more real primary colors of the pixel need to be combined so that virtual primary colors R, G and B can be created. Using only a few components of the colors of the second and third sub-pixels, the color of the first sub-pixel is achieved by all or substantially all of the colors of the first sub-pixel. Can lead to a relatively small color gamut. Thus, the indicated color of the green sub-pixel may be changed, for example using red and / or blue.

  The inventors of the present invention have found that the color gamut of the display is excessively reduced in this way. That is, there are colors that are outside the reduced color gamut triangle RGB, but still reach all pixels. These colors are included in the color field indicated by the shaded areas A1, A2 and A3 in FIG. These areas are referred to as color fields in the remainder of this description.

  Thus, according to the present invention, this reduced color gamut is expanded by using target primaries other than the virtual primaries R, G, B. These other target primaries are referred to in this document as “virtual target primaries” or “virtual target primary colors”. The virtual target primary color is selected so that most pixels of the display, ie at least 80% of the pixels of the display, can be reached. The selection of the virtual target primary color depends on the application in which the display is used. Depending on the application, color saturation is more important than color uniformity, and vice versa, which provides other options for virtual target primaries.

  Examples of virtual target primaries that can be used in the calibration algorithm of the present invention are indicated by points Rt, Gt and Bt in FIG. It can be seen that the color gamut RtGtBt extends the reduced color gamut RGB and that the colors within the new color gamut can be reached by most pixels of the display.

  Note that FIG. 3 and FIG. 4A described later show the color triangles of three and four pixels of display, respectively. However, the actual display includes much more than a few pixels, well hundreds, thousands, and even millions of pixels. A display device with 1 million pixels, 3 million pixels, 4 million pixels or 6 million pixels is not an exceptional display device. In particular, the drawings of FIGS. 3 and 4A are shown only to prepare the mind. For the sake of brevity, they do not show or illustrate the “at least 80%” feature of the present invention. As can be easily understood, it is practical to clearly show in the drawing the color triangles corresponding to all the pixels of the display device, even if it is a small display device containing only hundreds and thousands of pixels. Impossible. It is not easy to clearly distinguish the different colored triangles already shown with four pixels. Therefore, FIGS. 3 and 4A are not representative examples of the present invention. This is because in these drawings it is impossible to show that at least 80% but not all of the pixels can reach the selected virtual target primary. However, those of ordinary skill in the art, upon viewing FIGS. 3 and 4A and reading the description, what is meant, that is, there are more pixels that can reach the virtual target primary color, and only a few pixels, It is believed that less than 20% of the pixels cannot reach it.

An advantage of the present invention is that it is not necessary to add real primaries to the pixels to extend the color gamut. Adding a real primary color to a pixel means that the pixel contains four or more color elements, for example as described in WO 02/101644, rather than including three color elements. To do. Usually this is done by reducing the size of the three existing primary colors so that a fourth (or more) primary color can be added within the existing active pixel area. . However, in the case of an OLED, for example, reducing the size of the primary color active area reduces the lifetime of that color when it is driven in the same way. The addition of the fourth (or more) color component can be done by keeping the first three primary colors the same size and increasing the pixel size to add the fourth primary color. This loses resolution. Furthermore, the addition of primary colors further complicates the corresponding display drive circuit. The color coordinates of the virtual target primary colors Rt, Gt and Bt can be determined by the following method. Consider four pixels as shown in FIG. 4A. FIG. 4A shows a CIE color table having four separate pixel color gamuts for a light emitting fixed format display device. For example, the first pixel emits red R1, blue B1, and green G1. The color gamut of the first pixel is indicated by the triangle R1B1G1. The second pixel is red R
2, emit blue B2 and green G2. The color gamut of the second pixel is indicated by the triangle R2B2G2. The third pixel emits red R3, blue B3 and green G3. The color gamut of the third pixel is indicated by triangle R3B3G3. The fourth pixel emits red R4, blue B4 and green G4. The color gamut of the fourth pixel is indicated by triangle R4B4G4. Again, in practice, the display device contains much more than four pixels, and the color gamut of each of these pixels is measured. The reduced color gamut of the display that each and every pixel of the display device can reach is indicated by the color gamut triangle RGB. In the example shown in FIG. 4A, the point indicated by G is the point that gives the most saturated green that all pixels can reach, and the point indicated by R is the point that all pixels reach. The most saturated red possible, and the point indicated by B gives the most saturated blue that every pixel can reach for each pixel by manipulating the sub-pixel combination. A clear calculation of the virtual primaries R, G, B is not necessary. This is because R, G, and B need not be known to calculate the virtual target primary color. Thus, for ease of understanding, the positions of R, G, and B are shown in FIG. 4A. This is because it well illustrates the expansion of the color gamut realized with the virtual target primaries Rt, Gt and Bt.

  By defining a virtual target primary color, the color gamut of the entire display can be reached by a color gamut RtGtBt that can be reached by substantially all pixels of the display (eg, Rt1Gt1Bt1 or Rt2Gt2Bt2 depending on the choice made for the virtual target primary color). (Not shown as such in FIG. 4A).

  In the example shown in FIG. 4A, the point indicated by G is the point that gives the most saturated green that all pixels can reach, and the point indicated by R is the point that all pixels reach. Given the most saturated red possible, the point indicated by B gives the most saturated blue that every pixel can reach for each pixel by manipulating the sub-pixel combination. One method according to an embodiment of the present invention for calculating the color coordinates of a virtual target primary color may be as follows. To calculate the point Gt (Rt and Bt, respectively), the centroid Gz (Rz and Bz, respectively) of the quadrilateral G1G2G3G4 (R1R2R3R4 and B1B2B3B4, respectively) is first determined. Methods for determining the n-centroid centroid are known to those skilled in the art. These quadrilateral gravitational lines are also determined. The gravity line is an imaginary line through the center of gravity. In this case, the centroid is defined by a cloud of color points from multiple pixels for a single primary color. A particularly preferable gravity line is a line passing through the center of gravity toward the color target point of white K1 in FIG. However, the user can decide to select different gravitational lines depending on their preference. Such a preference might be, for example, that you do not want to add extra blue to the primary red. This is because it is desirable that the LED wall be similar to a CRT projector. Furthermore, color evaluation, particularly color evaluation through the eyes of the user, is a subjective perception problem. For example, what one user prefers as a saturated blue color may be different from what others prefer. In order to modify the primary color in a conventional manner, the direction of the selected gravity line can be changed away from the default line towards the white point. In this case, the number of LEDs that can reach the target point may be reduced. In addition, the change in the correction coefficient increases. This is because the distance from the primary color point to the target point further changes.

The target virtual primary color is then selected along or within 20% of the selected gravity line. For example, the CIEEx and CIEy color coordinate values of the target virtual primary color may be 20% greater or 20% smaller than the color coordinate value of any point placed on the gravity line. If a good color saturation display is desired but color uniformity is not important, the target virtual primary is close to the centroid, for example within 20% of the centroid, for example selected by Gt1, Rt1 and Bt1 in FIG. Is done. For example, the color coordinate values of the target virtual primary colors CIEx and CIEy may be 20% larger or 20% smaller than the color coordinate values of the center of gravity. If display color uniformity is very important, but color saturation is not important, the target virtual primaries move away from the center of gravity along the gravity line in the direction of the virtual primaries, as shown in FIG. 4A. Are moved to points Gt2, Rt2 and Bt2.

  Note that an actual display device typically includes much more than four pixels. Thus, the red, green and blue n-angles are rather red, green and blue clouds in the CIE color table, which in the real display device, rather contain the color coordinates of the real red, green and blue primaries, respectively. The cloud centroid and gravity lines of the actual primary color coordinates are further determined by performing appropriate numerical calculations and / or approximations.

  It is preferable to select the pixels so that the color coordinates of the actual primary color are included within a predetermined boundary line. Thereby, a display device tiled by another tile containing pixels having real primary colors contained within a predetermined boundary without having to redo all calculations to obtain an extended color gamut triangle It becomes possible to change the tile.

  One method according to an embodiment of the present invention for calculating the target brightness of the virtual target primary is shown in FIG. 4B. The vector TR in this figure indicates the primary primary red color. The direction of the vector TR is determined by the color coordinates of the virtual target primary color Rt that can be determined by the method described above. The length of this vector determines the brightness of the red primary color of the virtual target. The target brightness is set equal to the maximum brightness that all or substantially all pixels forming the display can achieve.

  In order to determine this maximum achievable target luminance, it is necessary to take into account the tristimulus vector of each primary color of each pixel. These stimulus vectors Rx, Gx and Bx for one pixel (ie, pixel x) of the display having the actual primary colors are shown in FIG. 4B. The maximum achievable target luminance of the virtual target primary color Rt that can be realized with this pixel x is determined by the intersection of the vector TR and the plane passing through the end point of the vector Rx and parallel to the plane formed by the vectors Bx and Gx. Is done. The same inference should be made for all pixels of the display device. The minimum vector TR determined by such a method determines a target luminance that can be realized by all the pixels of the display device. Depending on the application, the target brightness can be determined by selecting the length of the vector TR that can be achieved by substantially all the pixels of the display device, for example 80% of the pixels of the display device. .

  The above describes how the target brightness of the red virtual target primary color is determined. The target brightness of the blue and green virtual target primaries is determined in a similar manner.

  Once the color coordinates and target luminance of the virtual target primaries Rt, Gt and Bt for display are determined, all colors shown in the display device are driven to driving pixel stimuli for the pixel color elements, or hence sub It has to be converted into pixel driving stimuli. For example, when color K1 (FIG. 4A) is shown, the applied drive stimulus is known as a function of virtual target primaries such as Rt1, Gt1 and Bt1 as shown in equation (1), for example. Calculations are made for tristimulus values X, Y and Z.

  The drive stimuli for Rt1, Gt1 and Bt1 are then converted into drive stimuli for the relevant pixels, eg when color K1 has to be represented by a first pixel having real primary colors R1, G1 and B1 The driving stimuli of the virtual target primary colors Rt1, Gt1 and Bt1 are converted into the driving stimuli of the actual primary colors R1, G1 and B1.

  This can be done as follows. The color coordinates (x, y) and luminance Y of each primary color Rp, Gp, Bp of each pixel, that is, tristimulus values X, Y and Z are known. Correction values for red R1, green G1, and blue B1 for reproducing the new virtual target primary colors Rt1, Gt1, and Bt1 can be calculated as follows. This calculation should be performed for tristimulus values X, Y and Z (Equation 2).

By solving this set of linear equations, the correction values C ₁ to C ₉ can be determined. The actual primary red R1, green G1 and blue B1 drive axes to represent color K1 are then calculated by substituting equation (2) into equation (1) to yield equation (3). can do.

In accordance with another aspect of the present invention, if it must represent a color that falls outside the display gamut or extended gamut and / or must represent a color that all pixels of the display device cannot reach, Equation (1) To (3), the negative component of the driving stimulus must be given. For example, color K4 is outside the color gamut and is further outside the extended color gamut of the display (see FIG. 4A). This means that color K4 cannot be represented by every pixel of the display. As can be seen from FIG. 4A, the color K4 can be indicated by the first pixel (primary colors R1, G1, B1) and by the fourth pixel (primary colors R4, G4, B4), but the second pixel ( It cannot be represented by the primary colors R2, G2, B2) or by the third pixel (R3, G3, B3). In order to represent the color K4 by the second pixel, a negative stimulus value must be given to the blue component B of the pixel P2. However, it is physically impossible to give negative stimulus values.

  In the prior art, this problem is solved by setting the negative stimulus value to zero. However, this can lead to poor colors. This is because a positive correction value is overestimated.

  In accordance with an aspect of the present invention, rather than simply setting the negative stimulus value to zero, a color K4 that cannot be represented is projected at right angles to a plane that spans the two primary colors, which represent the color K4. Get a positive stimulus when you try to do it. This means that not only negative stimulus values are set to zero, but other stimulus values can or can be modified. This is illustrated in FIG. 5 and shows a color space spanning three real or virtual primary colors R, G and B. FIG. 5 is drawn in a tristimulus X, Y, Z color coordinate system. In FIG. 5, the color K4 cannot be represented by real or virtual primary colors R, G, B. This is because K4 has a negative driving stimulus value for the G primary color. When the negative stimulus value is set to zero, a color corresponding to K4 'is obtained, which corresponds to the R and B drive stimulus values that are the same as representing color K4. In accordance with the present invention, by projecting the color K4, which cannot be represented, onto the plane extending to B and R at right angles, a color corresponding to K4 "is obtained, which is the first time that it is intended to represent the color K4. Corresponding to the driving stimulus values for R and B, which may be different from those calculated, it can easily be seen from Fig. 5 that the driving stimulus values for at least the primary color R are different from those originally calculated. It can be seen that the orthogonal projection of the unrepresentable color point is closer to the desired unrepresentable color point than the color point obtained by setting the negative drive stimulus value to zero. .

  Right-angle projection onto the color plane can be done by a vector product.

  By doing this, the color closest to the color desired to be displayed is achieved.

  The advantage of the above method according to the present invention for representing colors outside the pixel gamut triangle is that when these colors are effectively represented in the gamut over the prior art methods. It is represented by a color that exists in the vicinity of the color that is actually desired but cannot be represented.

In an aspect of the present invention, a fixed format light emitting display device is provided, and the display device has a plurality of pixels. Each pixel has at least 3 to emit light of a different real primary color
Contains one subpixel. The display device separately determines at least one of the pixels of the display device separately for each real primary color by determining the centroid of the cloud formed by the color coordinates of the corresponding real primary color of all the pixels of the display device. Includes means for determining the color coordinates of the virtual target primaries that can be reached by 80%. Means for determining the color coordinates of the virtual target primaries are a microprocessor, application specific integrated circuit (ASIC), programmable logic array combined with a kind of memory for storing the color coordinates of the actual primary colors of the display device (PLA), programmable array logic (PAL), or field programmable gate array (FPGA). The display device also adjusts the drive current to the sub-pixel for the means for determining the color gamut defined by the determined virtual target primary color, and for pixels that cannot reach the virtual target primary color, Means for achieving a color within the determined color gamut. The means for determining the color gamut may be the calculation means as described above, and the means for adjusting the drive current may be a control device.

  The color calibration algorithm of the present invention can be implemented using an OLED module processing system (suitable for use in a large screen OLAD display), and a simplified function having only relevant components of the processing system. A block diagram is shown in FIG. 6A. The color coordinates of each OLED device in the OLED circuit are stored in the EEPROM 360 in the form of (xyY), where x and y are the color coordinates of the primary color emitter and Y is defined as brightness. Other information may be stored in the EEPROM 360 at any time without departing from the spirit and scope of the present invention. Communication to the EEPROM is accomplished via the EEPROM I / O bus.

  The EEPROM 360 is any type of electrically erasable storage medium. EEPROM 360 also stores the most recently calculated color calibration value used for the previous video frame.

  The OLED circuit 310 includes a plurality of OLED devices with associated drive circuits, which include a positive power supply, a constant current driver, and a plurality of active switches. Bank switching for connecting a positive power supply to a row of the OLED array in the OLED circuit is controlled by the VOLED CONTROL bus of the bank switching controller 320. The active switch that connects the constant current driver to the column of the OLED array in the OLED circuit is controlled by the PWM CONTROL bus of the CCD controller 330.

  Module interface 370 collects, among other things, current color coordinate information (tristimulus values in the form of x, y, Y) from EEPROM 360 for each OLED device in OLED circuit 310. The module interface 370 also receives control information from the tile processing system, i.e., the CONTROL (X) bus, which instructs the preprocessor 340 how to perform color calibration for the current video frame.

  Preprocessor 340 uses information from module interface 370 to develop, among other things, local color calibration of the current video frame. The preprocessor 340 combines the RGB data of the RGB (X) signal to the display device representing the current video frame with a newly developed color calibration algorithm, for the bank switching controller 320 and the CCD controller 330. Generate digital control signals, namely BANK CONTROL and CCD CONTROL buses, respectively. These signals strictly dictate which OLED device in OLED circuit 310 illuminates with which intensity and with which color to produce the desired frame with the required resolution and color calibration level.

The CCD controller 330 converts the data from the preprocessor 340 into a PWM signal, ie, a PWM CONTROL bus, and supplies different amounts of current to the OL in the OLED circuit 310.
Drives the current source that feeds the ED array. Each pulse width in the PWM CONTROL bus dictates the time at which the power supply associated with a given OLED device is activated and delivers current. Further, the CCD controller 330 transmits information to each current source related to the amount of current that drives the information. The amount of current that each CCD drives is determined by the preprocessor 340 based on the color correction algorithm and the RGB (X) signal.

  The bank switching controller 320 receives bank control data from the preprocessor 340, that is, the BANK CONTROL bus, and transmits this control data to the corresponding OLED via the VOLED CONTROL bus.

  The color calibration algorithm according to the present invention can be used in modular displays and fixed size displays. The following description shows the case of a modular display device. For a fixed size display device, the description can be modified if there is only one level of software. The color calibration algorithm is the applicant's co-pending patent entitled “Control system for a tiled large-screen emissive display”. It can be implemented using a high level software control system as described in the application.

  According to an embodiment of the present invention, the display device may have a plurality of display modes. Depending on the application, different display modes may be selected, each display mode corresponding to a particular selection of virtual target primaries. Furthermore, the calibration can be adapted on demand, for example, some applications may require good color uniformity, but in other applications color saturation is better. May be important. A compromise must be found between uniformity and saturation. For example, if the source material includes HDTV material (large color triangles), it may be desirable to increase saturation. In other cases, if the source material itself cannot reach the general LED triangle (which is even larger), it is useless to focus on good color saturation, in which case all the focus colors Will be placed on the uniformity.

  FIG. 6B shows a functional block diagram of the (O) LED software display system 60. The illustrated (O) LED soft display system 60 includes a system software component 61, a tile software component 62 and a module software component 63. (O) LED soft display system 60 provides overall software control for a modular large screen (O) LED display system. System software component 61 represents the highest level of software control, tile software component 62 represents the intermediate level software control, and module software component 63 represents the lower level software control. In operation, information passes between all levels and certain processes are distributed accordingly under the control of system software component 61. More specifically, referring to FIG. 6B, the system software component 61, which is the highest level controller, performs, among other things, an (O) LED tile adaptive calibration algorithm.

  As an intermediate level controller, tile software component 62 performs (among other things) an adaptive calibration algorithm for (O) LED modules.

As a low level controller, the module software component 63 executes (among other things) an adaptive calibration algorithm for individual (O) LED devices or pixels. In general, the calibration algorithm is basically the same at all levels of the (O) LED soft display system 60. This algorithm is performed by the tile software component 62 and / or the module software component 63, but the decision or information gathering typically takes place at the highest level by passing values from one level to the next. This is done by the system software component 61. Therefore, (O) LED device cluster, (O) L
The cluster of ED modules and the cluster of (O) LED tiles are similarly calibrated via the (O) LED soft display system 60.

  For example, a uniform output across all (O) LED devices in a given (O) LED module is ensured via an adaptive calibration algorithm, which allows all ( O) Uniform output across LED modules is not guaranteed. Subsequently, once the (O) LED module is uniform within itself, all (O) LED module outputs must be made more uniform with the neighborhood within each (O) LED tile. Similarly, once the (O) LED tile is uniform within itself, all (O) LED tile outputs must be made more uniform with the vicinity in each (O) LED back display of the display wall. Don't be. Using an adaptive calibration algorithm, the same algorithm is run at all levels from lowest to highest as follows:

  1) The adaptive calibration algorithm of module software component 63 reads the x, y, Y light output and color coordinates for all (O) LED devices of each (O) LED module. The coordinates of the optimal target x, y, Y are then calculated. The value is then passed to the next higher level, ie, tile software component 62.

  2) The adaptive calibration algorithm of tile software component 62 reads the optimal target xyY light output and color coordinates of each (O) LED module for each (O) LED tile. The coordinates of the optimal target x, y, Y are subsequently calculated. The value is then passed to the next higher level, ie the system software component 61.

  3) The adaptive calibration algorithm of the system software component 61 reads and calibrates all (O) LED tiles for each (O) LED back display of the display wall. Each (O) LED back display is subsequently calibrated to an optimal target (O) LED back display in the coordinates of the display wall x, y, Y. In this way, a uniform image is guaranteed over the entire display wall.

  While preferred embodiments, specific structures and configurations, and materials for devices in accordance with the present invention have been described herein, various changes in form and detail may be made without departing from the scope and spirit of the invention. Or it should be understood that modifications may be made.

FIG. 2 is a CIE diagram that is a European broadcast standard, and a diagram illustrating the color output of certain OLEDs and LED materials. 1 is a cross-sectional view of a typical OLED pixel structure. FIG. 4 illustrates the gamut of three different pixels and the reduced gamut expansion according to an embodiment of the present invention. FIG. 4 illustrates the method used to extend the gamut of four different pixels and the reduced gamut according to an embodiment of the present invention. FIG. 6 illustrates a method used to calculate a target luminance of a target virtual primary color according to an embodiment of the present invention. FIG. 4 illustrates a method according to an embodiment of the present invention for representing a color outside the color space spanning the RGB color space and the primary colors that define the color space. FIG. 2 is a simplified functional block diagram of an OLED module processing system that implements the color calibration algorithm of the present invention suitable for use in a large screen display device. It is a functional block diagram of the light emission type soft display system according to the present invention.

Explanation of symbols

60 (O) LED software display system, 61 system software component, 62
Tile software component, 63 module software component, 310 OLED circuit, 320 bank switching controller, 330 CCD controller, 340 preprocessor, 360 EEPROM, 370 module interface.

Claims (20)

A calibration method for calibrating a fixed format light emitting display device having a plurality of pixels, each pixel including at least three subpixels for emitting light of different real primary colors, the method comprising:
Separately determining for each real primary color the color coordinates of the virtual target primary color that can be reached by at least 80% of the pixels of the display device;
Determining a color gamut defined by the determined virtual target primary color;
Adjusting a drive current to the sub-pixel to achieve a color within the determined color gamut for pixels that cannot reach a virtual target primary color,
Determining the color coordinates of the virtual target primaries includes determining the centroid of the cloud formed by the corresponding real primaries color coordinates of all pixels of the display device.   The calibration method according to claim 1, wherein the value of the color coordinate determined for a virtual target primary color differs from the value of the color coordinate of the center of gravity of the cloud by up to 20%.   Calibration according to claim 1 or 2, further comprising the step of determining a gravitational line of the cloud formed by the color coordinates of the real primaries of all pixels of the display device corresponding to the determined virtual target primaries. Method.   Selecting the color coordinates of the virtual target primary color on or at a distance from the gravity line so that the color coordinate value of the virtual target primary color differs from the color coordinate value of the point placed on the gravity line by up to 20%. The calibration method according to claim 3, further comprising:   The target brightness of each target primary color is determined such that all or substantially all of the actual primary colors can achieve the target brightness of the corresponding virtual primary color, and the drive current for the sub-pixel is the target brightness The calibration method according to claim 1, wherein the calibration method is adjusted to achieve the following.   The calibration method according to claim 1, comprising the step of determining a virtual target primary color that can be achieved by all the pixels of the display device.   The calibration method according to claim 6, wherein the determination of the target luminance of the virtual target primary color depends on an application in which the display device is used.   The calibration method according to claim 6, wherein the target brightness of the virtual target primary color is selected to provide improved brightness uniformity.   The calibration method according to claim 6, wherein the target brightness of the virtual target primary color is selected to give a high absolute brightness value.   The calibration method according to claim 6, wherein the step of determining the target luminance of the virtual target primary color is performed after the virtual target primary color is first determined.   The calibration method according to claim 1, comprising the step of determining a color gamut that can be achieved by all the pixels of the display device.   The calibration method according to claim 1, wherein the color gamut is formed using a linear combination of the virtual target primary colors.   The calibration method according to claim 1, wherein the step of determining the color coordinates of a virtual target primary color separately for each primary color depends on the application in which the display device is used.   The calibration method of claim 13, wherein the virtual target primary color is determined to give better results with respect to color saturation than with respect to color uniformity.   The calibration method of claim 13, wherein the virtual target primaries are determined to give better results in terms of color uniformity than in terms of color saturation.   The calibration method according to any of claims 1 to 15, further comprising the step of repeating the calibration method after it has been performed at least once.   The calibration method according to claim 1, wherein the number of virtual target primary colors is equal to the number of actual primary colors.   In order to achieve a color within the determined color gamut, adjusting the drive current to the sub-pixel includes not only a first real primary color having a negative drive stimulus value, but also a positive drive stimulus. 18. A calibration method according to any of the preceding claims, comprising adjusting the drive current of at least one other real primary color having a value.   The step of adjusting the drive currents of the first real primary color and the at least one other real primary color is such that the color achieved within the determined color gamut is projected at right angles on a plane in the stimulus coordinate system. 19. The calibration method of claim 18, wherein the calibration method is performed and the surface spans two actual primary color stimulus coordinates having no negative drive stimulus. A fixed format light emitting display device having a plurality of pixels, each pixel including at least three sub-pixels for emitting light of different real primary colors, the display device comprising:
By determining the centroid of the cloud formed by the color coordinates of the corresponding real primary colors of all the pixels of the display device, at least 80% of the pixels of the display device are reached separately for each real primary color Means for determining the color coordinates of a virtual target pixel capable of
Means for determining a color gamut defined by the determined virtual target primary color;
Means for adjusting a drive current to the sub-pixel to achieve a color within the determined color gamut for pixels that are unable to reach a virtual target primary color.

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