Display screen comprising light-emitting diode (LED) display pixels

Abstract

Display screen comprising LED display pixels. This description relates to a display screen (10) comprising a matrix of display pixels, each pixel comprising at least one LED. The display screen further comprises a first circuit (60) configured to receive initial video data (V_IN) and to apply gamma decoding to the received initial video data (V_IN) to produce gamma-corrected video data (V_G), a second circuit (62) configured to receive a brightness setpoint (B_SET), a third circuit (64) configured to provide a reduction factor (FD) that depends on the brightness setpoint (B_SET), and a fourth circuit (66) configured to multiply the gamma-corrected video data (V_G) by the reduction factor (FD) to provide brightness- and gamma-corrected video data (V_GB). Figure for the abstract: Fig. 5

Description

Title of the invention: Display screen comprising light-emitting diode display pixels Technical field

[0001] The present description relates generally to display screens comprising light-emitting diode display pixels. Prior art

[0002] A pixel of an image corresponds to the unit element of the image displayed by a display screen. For the display of color images, a display screen generally comprises, for the display of each pixel of the image, at least three components, also called display sub-pixels, which each emit light radiation of substantially a single color (for example, red, green and blue). The superposition of the radiation emitted by the three display sub-pixels provides the observer with the colored sensation corresponding to the pixel of the displayed image. In this case, the assembly formed by the three display sub-pixels used for the display of a pixel of an image is called a display pixel of the display screen. Each display sub-pixel may comprise a light source, in particular a light-emitting diode.

[0003] The display pixels of a display screen may be arranged in a matrix, with each display pixel located at the intersection of a row (also called a line) and a column of the matrix. Electrodes are arranged along the rows and columns to connect each display pixel to the control circuits. Typically, a selection and timing circuit is connected to the row electrodes. Each row of display pixels is successively selected by a signal transmitted along the row electrodes by the selection and timing circuit, and the display pixels in the selected row are programmed to display the desired image pixels by signals transmitted along the column electrodes.

[0004] An active matrix is ​​a screen reader architecture that allows all rows of pixels to be kept active for the entire duration of an image, unlike so-called passive matrices, where each row is only active for a time T = Tframe / M (where Tframe corresponds to the display time of the entire image and M corresponds to the number of lines on the screen). This allows the brightness of the display screen to be increased. Furthermore, it is possible to send low levels of voltage or current to the control lines of the matrix, which allows larger data streams to be displayed.

[0005] The control of a light-emitting diode by width modulation is known. pulse, also called PWM (English acronym for Pulse Width Modulation). This type of control consists of circulating successive current pulses of constant intensity in the light-emitting diode, the pulses repeating cyclically, the duty cycle determining the light intensity emitted by the light-emitting diode. Such control advantageously makes it possible to operate the light-emitting diode at its optimal operating point where the efficiency of the light-emitting diode, equal to the ratio between the light power emitted by the light-emitting diode and the electrical power consumed by the light-emitting diode, is maximum. A PWM control generally requires the selection and synchronization circuit to emit a succession of pulses on the row electrodes, the durations between the pulses depending on the image pixel to be displayed.

[0006] A display screen generally also includes an adjustment for varying the overall brightness of the displayed image. One way to decrease the brightness of a displayed image from a maximum brightness is to decrease the durations between the pulses of the transmission by the selection and synchronization circuit.

[0007] One disadvantage is that it may be difficult for the selection and timing circuit to provide pulses separated by short durations when the brightness is set to be low. There may be a limit to the minimum brightness that can be achieved. Another disadvantage is that the selection and timing circuit must be able to provide many different successions of pulses separated by different durations depending on the brightness settings. Summary of the invention

[0008] An object of an embodiment is to propose a display screen comprising light-emitting diodes overcoming all or part of the drawbacks of known display screens.

[0009] Another object of an embodiment is that the selection and synchronization circuit delivers the same succession of pulses for a PWM command, regardless of the brightness setpoint.

[0010] Another object of an embodiment is that there is no limit to the minimum brightness that can be achieved.

[0011] Another object of an embodiment is that the structure of the selection and synchronization circuit is simple.

[0012] One embodiment provides a display screen comprising an array of display pixels each comprising at least one light emitting diode, the display screen further comprising a first circuit configured to receive initial video data and to apply gamma decoding to the video data. initial received to produce gamma-corrected video data, a second circuit configured to receive a brightness command, a third circuit configured to provide a roll-off factor that depends on the brightness command, and a fourth circuit configured to multiply the gamma-corrected video data by the roll-off factor to provide brightness- and gamma-corrected video data. The brightness correction is applied to the video data before it is transmitted to the display pixels. Therefore, the display pixels can advantageously operate independently of the brightness correction. In addition, there can advantageously be no limit to the minimum brightness that can be achieved.

[0013] According to one embodiment, the display pixels are arranged in rows and columns, the display screen further comprising a data driving circuit configured to provide the video data to the columns of display pixels based on the brightness and gamma corrected video data. Therefore, the display pixels can advantageously operate independently of the brightness correction.

[0014] According to one embodiment, each display pixel comprises a data driving circuit configured to determine a digital signal from the video data and to control the light-emitting diode according to the digital signal.

[0015] According to one embodiment, the data control circuit is configured to control the light-emitting diode by pulse width modulation from the digital signal. Such control advantageously makes it possible to operate the light-emitting diode at its optimal operating point where the efficiency of the light-emitting diode is maximum.

[0016] According to one embodiment, the display screen comprises a selection and synchronization circuit configured to provide a succession of pulses to each row of display pixels. The pulses delivered by the selection and synchronization circuit are, during a display phase, advantageously the same regardless of the brightness setting. Consequently, the structure of the selection and synchronization circuit can be simple.

[0017] According to one embodiment, the control circuit is configured to turn on or off the light-emitting diode at the rate of the succession of pulses.

[0018] Another embodiment provides a method of displaying images by a display screen comprising a matrix of display pixels each comprising at least one light-emitting diode, comprising the following steps; - reception of initial video data; - applying gamma decoding to the initial video data received to produce gamma-corrected video data; - receipt of a brightness instruction; - provision of a reduction factor which depends on the brightness setting; - multiplication of gamma-corrected video data by the reduction factor to provide brightness and gamma-corrected video data.

[0019] According to one embodiment, the display pixels are arranged in rows and columns, the method further comprising the step of providing the video data to the columns of display pixels based on the brightness and gamma corrected video data.

[0020] According to one embodiment, each display pixel comprises a driving circuit configured to determine a digital signal from the video data and to control the light-emitting diode as a function of the digital signal.

[0021] According to one embodiment, the driving circuit is configured to control the light-emitting diode by pulse width modulation from the digital signal.

[0022] According to one embodiment, the method consists of providing a succession of pulses to each row of display pixels.

[0023] According to one embodiment, the control circuit is configured to turn on or off the light-emitting diode at the rate of the succession of pulses. Brief description of the drawings

[0024] These characteristics and advantages, as well as others, will be explained in detail in the following description of the particular embodiments given without limitation in relation to the attached figures among which:

[0025] [Fig.l] partially and schematically represents an example of a display screen;

[0026] [Fig.2] shows an example of a functional diagram of a display pixel of the display screen of [Fig.l];

[0027] [Fig. 3] shows examples of timing diagrams of a signal used by the display pixel of [Fig. 2] to control a light-emitting diode by pulse width modulation and the current delivered to the light-emitting diode;

[0028] [Fig.4] represents examples of timing diagrams of a synchronization signal and current pulses for controlling a light-emitting diode by pulse width modulation for different brightness setpoints;

[0029] [Fig.5] represents an embodiment of a functional diagram of a circuit of the display screen of [Fig.l] for varying the brightness of the displayed images;

[0030] [Fig.6] represents a curve of evolution of a reduction factor determined by the circuit of [Fig.5] as a function of the brightness instructions;

[0031] [Fig.7] shows examples of equivalent gamma decoding functions implemented by the circuit of [Fig.5] and

[0032] [Fig.8] shows examples of timing diagrams of a synchronization signal and current pulses for controlling a light-emitting diode by pulse width modulation for different brightness settings using the circuit of [Fig.5]. Description of the embodiments

[0033] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties. For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been shown and are detailed.

[0034] When referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures or to a display screen in the normal position of use.

[0035] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0036] Furthermore, a "binary signal" is a signal that alternates between a first constant state, for example a low state, denoted "0", and a second constant state, for example a high state, denoted "1". The high and low states of different binary signals of the same electronic circuit may be different. In practice, the binary signals may correspond to voltages that may not be perfectly constant in the high or low state.

[0037] Furthermore, unless otherwise indicated, when referring to a voltage at a conductive pad, the difference between the potential at said conductive pad and a reference potential, for example ground, is considered to be equal to 0 V.

[0038] Unless otherwise specified, the expressions “about”, “approximately”, “substantially”, and “of the order of” mean to within 10%, preferably to within 5%.

[0039] [Fig. 1] partially and schematically represents a known example of a display screen 10. The display screen 10 comprises display pixels 1¾, for example example, arranged in M ​​rows and N columns, M being an integer varying from 1 to 8,000 and N being an integer varying from 1 to 16,000, i being an integer varying from 1 to M, and j being an integer varying from 1 to N. For example, in [Fig.l], M and N are equal to 6. Each display pixel 1¾ is coupled to a source of low reference potential Gnd, for example ground, via an electrode 14; and to a source of high reference potential Vcc via an electrode 16j. For example, the electrodes 14; are shown aligned along the rows in [Fig.l] and the electrodes 16j are shown aligned along the columns in [Fig.l], the reverse arrangement being possible. The display screen supply voltage corresponds to the voltage between the high reference potential Vcc and the low reference potential Gnd, and is denoted Vcc as the high reference potential.The supply voltage Vcc depends in particular on the arrangement of the light-emitting diodes and the technology by which the light-emitting diodes are manufactured. For example, the supply voltage Vcc can be in the order of 4 V to 5 V.

[0040] For each row, the display pixels 12;j of the row are coupled to a row electrode 18;. For each column, the display pixels 12;j of the column are coupled to a column electrode 20j. The display screen 10 comprises a selection and synchronization circuit 22 coupled to the row electrodes 18; and adapted to provide a selection and synchronization signal Corn; on each row electrode 18;. The display screen 10 comprises a data supply circuit 24 coupled to the column electrodes 20j and adapted to provide a data signal Dataj on each column electrode 20j. The selection and synchronization circuit 22 and the control circuit 24 are controlled by a circuit 26, comprising for example a processor. The circuit 26 receives video data V_IN and a brightness setpoint B_SET. The data signal Dataj is generated from the video data V_IN.

[0041] [Fig. 2] represents an example of a functional diagram of a display pixel 1¾ of the display screen 10. For a color display screen, the display pixel 1¾ comprises a light-emitting circuit comprising at least three light-emitting diodes LED emitting radiation of different colors, a single light-emitting diode LED being represented in [Fig. 2]. Each light-emitting diode LED is coupled in series to a controllable current source SC, comprising for example a MOS transistor in series with a current source delivering a constant current. In the present example, for each light-emitting diode LED, the anode of the light-emitting diode LED receives the high reference potential Vcc and the cathode of the light-emitting diode LED is, for example, coupled to one terminal of the controllable current source SC, the other terminal of the controllable current source SC receiving the low reference potential Gnd. In the In the case of a monochrome display screen, each 12y display pixel may comprise a light-emitting circuit comprising a single light-emitting diode LED.

[0042] The display pixel 12ÿ further comprises a driving circuit 40 for driving the controllable current source SC. The driving circuit 40 may in particular comprise electronic components such as MOS transistors. The driving circuit 40 comprises a storage circuit 48 (color data registers) clocked by a clock signal Clk configured to store digital color signals R, G, B as a function of the received digital data Data. The digital color signals R, G, B each comprise a number NB of bits, from the most significant bit, called MSB, to the least significant bit, called LSB, and are representative of the color components of the pixels of the image to be displayed. The driver circuit 40 comprises a circuit 50 (LED driver) configured to control the controllable current sources SC coupled to light-emitting diodes LED with signals I_red, I_green and I_blue, obtained from digital color signals R, G, B, and a PWM signal.The data Data may correspond to the signal Dataj transmitted to the display pixel 12ij on the column electrode 20j during a selection phase. The PWM signal may correspond to the selection and synchronization signal Com; transmitted to the display pixel 12ij on the row electrode 18; during a display phase.

[0043] [Fig. 3] represents a timing diagram of the PWM signal and the signals I_red_l, I_red_2, I_red_3 and I_red_4 corresponding to the signal I_red delivered by the circuit 50 of the display pixel 12;j of [Fig. 2] for the display of four different color digital signals R. According to one embodiment, the light-emitting diodes LED of the display pixel 12;j are controlled by pulse width modulation. For this purpose, during a display phase, the PWM signal has a succession of pulses in the logic state “1” which sets the pace for the operation of the control circuit 50 of light-emitting diodes LED by pulse width modulation. The number of pulses in the succession of pulses can correspond to the number NB+1.

[0044] For example, when the current source SC corresponds to a current source delivering a constant current in series with a MOS transistor, the MOS transistor is on or off according to the logic value “0” or “1” of each bit of the color signal R, G or B, from the most significant bit MSB to the least significant bit LSB, at the rate of the pulses of the PWM signal, the MOS transistor being kept on or off until the next pulse of the PWM signal. Thus, the current source SC is switched on or off for NB successive durations according to the logic values ​​of the bits of the digital signal R, G or B. For example, the current source SC can be switched on for a duration where the bit of the color digital data associated with this time interval is at the logic value “1” and can be switched off for a duration where the bit of the digital color data associated with this time interval is at the logic value "0". The duration between two successive pulses of the PWM signal is divided by two each time, so that the total duration during which the light-emitting diode is lit depends on the value of the R, G or B color signal. The succession of pulses of the PWM signal can be repeated until another pixel of the image is displayed. In this case, the succession of pulses of the PWM signal forms a display cycle and the display phase comprises more than one display cycle.

[0045] In [Fig.3], as an example, the number NB is equal to 7 and only one cycle display is shown. The signal I_red_l is obtained for displaying an image pixel color component corresponding to the color signal R equal to "1010101". The signal I_red_2 is obtained for displaying an image pixel color component corresponding to the color signal R equal to "0101010". The signal I_red_3 is obtained for displaying an image pixel color component corresponding to the color signal R equal to "1111111". The signal I_red_4 is obtained for displaying an image pixel color component corresponding to the color signal R equal to "0000000".

[0046] Typically, the circuit 26 of the display screen 10 also receives a B_SET instruction to vary the overall brightness of the displayed image. This B_SET instruction may be separate from the video data received by the circuit 26. For example, the brightness instruction may be controlled by the person viewing the display screen 10. One way to decrease the brightness of a displayed image relative to a maximum brightness is to decrease the duration of a display cycle relative to the maximum duration Tmax of a display cycle used for maximum brightness, the light-emitting diode LED being off for the remainder of the duration Tmax.

[0047] [Fig.4] represents timing diagrams of the PWM signal and the I_red signal delivered by circuit 50 of display pixel 1¾ of [Fig.2] for displaying the same digital color signal “1010101” for three values ​​of a brightness setpoint. The upper signals correspond to the PWM signal and the I_red signal when the cycle time is equal to a maximum display cycle time Tmax. The middle signal corresponds to the PWM signal and the I_red signal when the cycle time is substantially equal to 50% of the maximum display cycle time Tmax. The lower signal corresponds to the PWM signal and the I_red signal when the cycle time is substantially equal to 10% of the maximum PWM cycle time Tmax.

[0048] Decreasing the duration of a PWM cycle relative to the maximum duration of the display cycle Tmax leads to the decrease of each duration associated with each bit of the color digital signal. This means that the pulses of the selection and synchronization signal Com; must be generated closer by the selection and synchronization circuit 22.

[0049] One difficulty is to generate the pulses to provide the shortest duration associated with the LSB. This is because the propagation time of the selection and synchronization signal Com; between the display pixel 1¾ and the synchronization circuit 22 varies depending on the position of the display pixel 1¾ on the display screen 10. In the arrangement shown in [Fig.l], the propagation time on the row electrodes 18; is shortest for the display pixels 1¾ on the first column which is closest to the selection and synchronization circuit 22 and is longest for the display pixels 1¾ on the last column which is furthest from the synchronization circuit 22. These different propagation times must be taken into account to ensure that, for each row, all the pulses of the selection and synchronization signal Com; during a display cycle are correctly transmitted to all the display pixels in the row.This may result in an upper limit on the operating speed of the display screen.

[0050] In addition, as shown in [Fig.4], different PWM signals must be sent to the display pixels depending on the brightness setpoint. This may result in a selection and synchronization circuit 22 having a complex structure to be able to generate many different PWM signals.

[0051] In addition, there is a limitation on the minimum brightness control range. For example, consider a display screen where the refresh rate is 120 Hz, the minimum pulse duration is 50 ns, and NB is 16. The minimum possible display cycle time is 50 ns times 216, or 3.28 ms. This corresponds to a minimum brightness equal to 39% of the maximum brightness.

[0052] [Fig. 5] represents a functional diagram of an embodiment of a part of the circuit 26 of the display screen 10.

[0053] Circuit 26 comprises: - a circuit 60 configured to receive video data V_IN, to receive a gamma instruction GAMMA and to apply a gamma correction to the received video data V_IN in order to provide successive gamma-corrected video data V_G; - a circuit 62 configured to receive the brightness instruction B_SET and to store the received brightness instruction B_SET; - a circuit 64 configured to receive the brightness setpoint B_SET stored in the circuit 62 and to provide a reduction factor FD and - a circuit 66 configured to multiply each successive gamma-corrected video data V_G with a reduction factor FD and to provide successive brightness and gamma-corrected video data V_GB.

[0054] Each received video data V_IN comprises NB bits. Each corrected video data in gamma V_G comprises NB+a bits. The additional number of "a" bits depends on the type of gamma correction that is performed by the circuit 60. The brightness setpoint comprises K bits. The reduction factor FD is between 0 and 1. Each brightness and gamma corrected video data V_GB comprises NB+a bits. The data signal Dataj can correspond to brightness and gamma corrected video data V_GB.

[0055] [Fig.6] represents a curve showing the evolution of the reduction factor FD in relation to the brightness setpoint B_SET. In the example shown in [Fig.6], the reduction factor FD varies linearly with the brightness setpoint B_SET.

[0056] Human eyes are much more sensitive to changes in dark tones than to similar changes in light tones. A photodetector typically provides an analog electrical image pixel signal that has a substantially linear relationship to the number of photons striking the sensor. If the display system operated with a digital control method such as pulse width modulation operation, a high number of bits would have to be used for the digital image pixel signals so that dark tones are described with sufficient accuracy. Low bit count digitization results in posterization of the displayed image for dark tones.

[0057] To optimize bit utilization when encoding an image and / or to optimize the bandwidth used to transport an image, a nonlinear operation, generally referred to as gamma coding or gamma compression, is applied to the image pixel signal provided by the photodetector to redistribute the tonal levels of the native image sensor into levels that are more perceptually uniform for human eyes. Gamma coding is, for example, defined by the following power-law expression:

[0058] [Math 1] Vout = Vimc where the non-negative real input value Vin is raised to the power yc to obtain the output value Vout, with, for example, Vin and Vout in the range 0-1. The exponent yc is usually equal to 1 / 2.2.

[0059] To display the image pixel, the inverse nonlinear operation, called gamma decoding or gamma expansion, is applied to the image pixel signal to efficiently convert it back to light from the original scene. Gamma decoding is, for example, defined by the following power law expression:

[0060] [Math 2] Vout = Vin'^ where the non-negative real input value Vin is raised to the power of y to obtain the output value Vout, with, for example, Vin and Vout in the range 0-1. The exponent yd is usually equal to 1 / yd, for example equal to 2.2.

[0061] The gamma decoding operation is performed by the circuit 60. The gamma setting GAMMA can correspond to the exponent yd, which is for example equal to 2, 2.2 or 2.4.

[0062] Multiplying each gamma-corrected video data V_G by the reduction factor FD is equivalent to resizing the gamma decoding function that is applied to the received video data V_IN.

[0063] [Fig.7] represents the equivalent gamma decoding function IgamlOO, Igam50, Igam25 applied to the received video data V_IN for different brightness setpoints B_SET corresponding to a brightness equal to 100% (curve IgamlOO), 50% (Igam50) and 25% (Igam25). In [Fig.7], the y axis indicates the number of levels of the brightness and gamma corrected video data V_GB and the x axis indicates the number of levels of the received video data V_IN. For tones to appear smooth and continuous in an image, it is generally sufficient to be able to code at least 256 different luminance levels, which should theoretically only require 8 bits.

[0064] As an example, Table 1 below includes: - in the first column entitled Grayscale (8 bits)”, the 256 grayscale values ​​in decimal notation which can be coded on 8 bits; - in the second column entitled “Linear Ideal (16-bits)”, the corresponding ideal obtained from the values ​​in decimal notation after a linear conversion that can be coded on 16 bits; - in the third column entitled “Ideal 2.2 (16 bits)”, the corresponding ideal obtained from the values ​​in decimal notation after a gamma conversion with yd equal to 2.2 can be coded on 16 bits; - in the fourth column entitled “100% brightness”, the corresponding real values ​​in decimal notation after multiplication by a reduction factor equal to 1; - in the fifth column entitled “50% brightness”, the corresponding real values ​​in decimal notation after multiplication by a reduction factor equal to 0.5 and - in the sixth column entitled “brightness 25%”, the corresponding real values ​​in decimal notation after multiplication by a reduction factor equal to 0.25.

[0065] [Tables 1] Grayscale (8-bit) Linear Ideal (16-bit) 2.2 Ideal (16-bit) Brightness 100% Brightness 50% Brightness 25% 0 0 0.00 0 0 0 1 511 1.51 2 1 1 2 767 3.69 4 2 1 3 1023 6.95 7 4 2 4 1279 11.36 11 6 3 5 1535 16.97 17 9 4 6 1791 23.83 24 12 6 7 2047 31.97 32 16 8 8 2303 41.43 41 21 10 9 2559 52.24 52 26 13 10 2815 64.43 64 32 16 11 3071 78.03 78 39 20 12 3327 93.06 93 47 23 13 3583 109.54 110 55 28 14 3839 127.50 128 64 32 15 4095 146.96 147 74 37 16 4351 167.93 168 84 42 17 4607 190.44 190 95 48 18 4863 214.50 214 107 54 19 5119 240.13 240 120 60 20 5375 267.34 267 134 67 21 5631 296.16 296 148 74 22 5887 326.59 327 164 82 23 6143 358.65 359 180 90 24 6399 392.35 392 196 98 25 6655 427.72 428 214 107 26 6911 464.75 465 233 116 27 7167 503,47 503 252 126 28 7423 543,88 544 272 136 29 7679 586,01 586 293 147 30 7935 629,85 630 315 158 31 8191 675,42 675 338 169 32 8447 722,73 723 362 181 33 8703 771,80 772 386 193 34 8959 822,63 823 412 206 35 9215 875,23 875 438 219 36 9471 929,61 930 465 233 37 9727 985,79 986 493 247 38 9983 1043,77 1044 522 261 39 10239 1103,57 1104 552 276 40 10495 1165,18 1165 583 291 41 10751 1228,63 1229 615 307 42 11007 1293,91 1294 647 324 43 11263 1361,04 1361 681 340 44 11519 1430,03 1430 715 358 45 11775 1500,88 1501 751 375 46 12031 1573,61 1574 787 394 47 12287 1648,21 1648 824 412 48 12543 1724,71 1725 863 431 49 12799 1803,10 1803 902 451 50 13055 1883,39 1883 942 471 51 13311 1965,60 1966 983 492 52 13567 2049,73 2050 1025 513 53 13823 2135,78 2136 1068 534 54 14079 2223,77 2224 1112 556 55 14335 2313,70 2314 1157 579 56 14591 2405,58 2406 1203 602 57 14847 2499,41 2499 1250 625 58 15103 2595,20 2595 1298 649 59 15359 2692,96 2693 1347 673 60 15615 2792,70 2793 1397 698 61 15871 2894,42 2894 1447 724 62 16127 2998,13 2998 1499 750 63 16383 3103,83 3104 1552 776 64 16639 3211,53 3212 1606 803 65 16895 3321,24 3321 1661 830 66 17151 3432,96 3433 1717 858 67 17407 3546,70 3547 1774 887 68 17663 3662,47 3662 1831 916 69 17919 3780,27 3780 1890 945 70 18175 3900,10 3900 1950 975 71 18431 4021,98 4022 2011 1006 72 18687 4145,90 4146 2073 1037 73 18943 4271,88 4272 2136 1068 74 19199 4399,92 4400 2200 1100 75 19455 4530,03 4530 2265 1133 76 19711 4662,20 4662 2331 1166 77 19967 4796,45 4796 2398 1199 78 20223 4932,79 4933 2467 1233 79 20479 5071,21 5071 2536 1268 80 20735 5211,72 5212 2606 1303 81 20991 5354,33 5354 2677 1339 82 21247 5499,04 5499 2750 1375 83 21503 5645,86 5646 2823 1412 84 21759 5794,79 5795 2898 1449 85 22015 5945,84 5946 2973 1487 86 22271 6099,01 6099 3050 1525 87 22527 6254,31 6254 3127 1564 88 22783 6411,74 6412 3206 1603 89 23039 6571,31 6571 3286 1643 90 23295 6733,02 6733 3367 1683 91 23551 6896,88 6897 3449 1724 92 23807 7062,89 7063 3532 1766 93 24063 7231,05 7231 3616 1808 94 24319 7401,38 7401 3701 1850 95 24575 7573,87 7574 3787 1894 96 24831 7748,53 7749 3875 1937 97 25087 7925,36 7925 3963 1981 98 25343 8104,38 8104 4052 2026 99 25599 8285,57 8286 4143 2072 100 25855 8468,96 8469 4235 2117 101 26111 8654,54 8655 4328 2164 102 26367 8842,31 8842 4421 2211 103 26623 9032,28 9032 4516 2258 104 26879 9224,46 9224 4612 2306 105 27135 9418,85 9419 4710 2355 106 27391 9615,45 9615 4808 2404 107 27647 9814,26 9814 4907 2454 108 27903 10015,3 0 10015 5008 2504 109 28159 10218,5 7 10219 5110 2555 110 28415 10424,0 6 10424 5212 2606 111 28671 10631,7 9 10632 5316 2658 112 28927 10841,7 5 10842 5421 2711 113 29183 11053,9 6 11054 5527 2764 114 29439 11268,4 1 11268 5634 2817 115 29695 11485,1 2 11485 5743 2871 116 29951 11704,0 7 11704 5852 2926 117 30207 11925,2 8 11925 5963 2981 118 30463 12148,7 6 12149 6075 3037 119 30719 12374,5 0 12374 6187 3094 120 30975 12602,5 1 12603 6302 3151 121 31231 12832,7 9 12833 6417 3208 122 31487 13065,3 4 13065 6533 3266 123 31743 13300,1 8 13300 6650 3325 124 31999 13537,3 0 13537 6769 3384 125 32255 13776,7 1 13777 6889 3444 126 32511 14018,4 1 14018 7009 3505 127 32767 14262,4 0 14262 7131 3566 128 33023 14508,7 0 14509 7255 3627 129 33279 14757,2 9 14757 7379 3689 130 33535 15008,1 9 15008 7504 3752 131 33791 15261,4 0 15261 7631 3815 132 34047 15516,9 2 15517 7759 3879 133 34303 15774,7 6 15775 7888 3944 134 34559 16034,9 1 16035 8018 4009 135 34815 16297,3 9 16297 8149 4074 136 35071 16562,2 0 16562 8281 4141 137 35327 16829,3 3 16829 8415 4207 138 35583 17098,8 0 17099 8550 4275 139 35839 17370,6 1 17371 8686 4343 140 36095 17644,7 5 17645 8823 4411 141 36351 17921,2 4 17921 8961 4480 142 36607 18200,0 7 18200 9100 4550 143 36863 18481,2 6 18481 9241 4620 144 37119 18764,8 0 18765 9383 4691 145 37375 19050,6 9 19051 9526 4763 146 37631 19338,9 4 19339 9670 4835 147 37887 19629,5 6 19630 9815 4908 148 38143 19922,5 4 19923 9962 4981 149 38399 20217,8 9 20218 10109 5055 150 38655 20515,6 1 20516 10258 5129 151 38911 20815,7 1 20816 10408 5204 152 39167 21118,1 9 21118 10559 5280 153 39423 21423,0 5 21423 10712 5356 154 39679 21730,2 9 21730 10865 5433 155 39935 22039,9 3 22040 11020 5510 156 40191 22351,9 5 22352 11176 5588 157 40447 22666,3 7 22666 11333 5667 158 40703 22983,1 8 22983 11492 5746 159 40959 23302,4 0 23302 11651 5826 160 41215 23624,0 1 23624 11812 5906 161 41471 23948,0 4 23948 11974 5987 162 41727 24274,4 7 24274 12137 6069 163 41983 24603,3 2 24603 12302 6151 164 42239 24934,5 8 24935 12468 6234 165 42495 25268,2 6 25268 12634 6317 166 42751 25604,3 6 25604 12802 6401 167 43007 25942,8 8 25943 12972 6486 168 43263 26283,8 3 26284 13142 6571 169 43519 26627,2 1 26627 13314 6657 170 43775 26973,0 2 26973 13487 6743 171 44031 27321,2 7 27321 13661 6830 172 44287 27671,9 5 27672 13836 6918 173 44543 28025,0 8 28025 14013 7006 174 44799 28380,6 5 28381 14191 7095 175 45055 28738,6 7 28739 14370 7185 176 45311 29099,1 3 29099 14550 7275 177 45567 29462,0 5 29462 14731 7366 178 45823 29827,4 3 29827 14914 7457 179 46079 30195,2 6 30195 15098 7549 180 46335 30565,5 5 30566 15283 7642 181 46591 30938,3 0 30938 15469 7735 182 46847 31313,5 3 31314 15657 7829 183 47103 31691,2 1 31691 15846 7923 184 47359 32071,3 8 32071 16036 8018 185 47615 32454,0 1 32454 16227 8114 186 47871 32839,1 2 32839 16420 8210 187 48127 33226,7 1 33227 16614 8307 188 48383 33616,7 9 33617 16809 8404 189 48639 34009,3 4 34009 17005 8502 190 48895 34404,3 9 34404 17202 8601 191 49151 34801,9 2 34802 17401 8701 192 49407 35201,9 5 35202 17601 8801 193 49663 35604,4 7 35604 17802 8901 194 49919 36009,4 9 36009 18005 9002 195 50175 36417,0 1 36417 18209 9104 196 50431 36827,0 3 36827 18414 9207 197 50687 37239,5 6 37240 18620 9310 198 50943 37654,5 9 37655 18828 9414 199 51199 38072,1 4 38072 19036 9518 200 51455 38492,2 0 38492 19246 9623 201 51711 38914,7 7 38915 19458 9729 202 51967 39339,8 6 39340 19670 9835 203 52223 39767,4 8 39767 19884 9942 204 52479 40197,6 1 40198 20099 10050 205 52735 40630,2 7 40630 20315 10158 206 52991 41065,4 6 41065 20533 10266 207 53247 41503,1 8 41503 20752 10376 208 53503 41943,4 3 41943 20972 10486 209 53759 42386,2 1 42386 21193 10597 210 54015 42831,5 4 42832 21416 10708 211 54271 43279,4 0 43279 21640 10820 212 54527 43729,8 1 43730 21865 10933 213 54783 44182,7 6 44183 22092 11046 214 55039 44638,2 6 44638 22319 11160 215 55295 45096,3 0 45096 22548 11274 216 55551 45556,9 0 45557 22779 11389 217 55807 46020,0 5 46020 23010 11505 218 56063 46485,7 6 46486 23243 11622 219 56319 46954,0 3 46954 23477 11739 220 56575 47424,8 6 47425 23713 11856 221 56831 47898,2 5 47898 23949 11975 222 57087 48374,2 1 48374 24187 12094 223 57343 48852,7 4 48853 24427 12213 224 57599 49333,8 4 49334 24667 12334 225 57855 49817,5 1 49818 24909 12455 226 58111 50303,7 5 50304 25152 12576 227 58367 50792,5 8 50793 25397 12698 228 58623 51283,9 8 51284 25642 12821 229 58879 51777,9 6 51778 25889 12945 230 59135 52274,5 3 52275 26138 13069 231 59391 52773,6 9 52774 26387 13194 232 59647 53275,4 3 53275 26638 13319 233 59903 53779,7 6 53780 26890 13445 234 60159 54286,6 9 54287 27144 13572 235 60415 54796,2 1 54796 27398 13699 236 60671 55308,3 3 55308 27654 13827 237 60927 55823,0 5 55823 27912 13956 238 61183 56340,3 7 56340 28170 14085 239 61439 56860,3 0 56860 28430 14215 240 61695 57382,8 3 57383 28692 14346 241 61951 57907,9 7 57908 28954 14477 242 62207 58435,7 2 58436 29218 14609 243 62463 58966,0 8 58966 29483 14742 244 62719 59499,0 6 59499 29750 14875 245 62975 60034,6 6 60035 30018 15009 246 63231 60572,8 7 60573 30287 15143 247 63487 61113,7 0 61114 30557 15279 248 63743 61657,1 6 61657 30829 15414 249 63999 62203,2 5 62203 31102 15551 250 64255 62751,9 6 62752 31376 15688 251 64511 63303,3 0 63303 31652 15826 252 64767 63857,2 7 63857 31929 15964 253 65023 64413,8 8 64414 32207 16104 254 65279 64973,1 2 64973 32487 16243 255 65535 65535,0 0 65535 32768 16384

[0066] [Fig.8] shows examples of timing diagrams of the PWM signal and the signals I_red_100, I_red_50 and I_red_25 delivered by the circuit 50 of the display pixel 12jj of [Fig.2] for the display of the same initial video data V_IN for three values ​​of a brightness setpoint. The gamma-corrected video data V_G for the initial video data V_IN correspond to the digital signal “1010101”. The signal I_red_100 corresponds to a brightness equal to 100%, i.e. a decay factor FD equal to 1, so that the brightness- and gamma-corrected video data V_GB also corresponds to the digital signal “1010101”. The I_red_50 signal corresponds to a brightness equal to 50%, or a decay factor FD equal to 0.5, so that the brightness and gamma corrected video data V_GB correspond to the digital signal “0101010”.The I_red_25 signal corresponds to a brightness equal to 25%, or a reduction factor FD equal to 0.25, so that the brightness and gamma corrected video data V_GB correspond to the digital signal “0010101”.

[0067] A brightness setpoint in the range of 0% to 100% can be achieved without requiring the generation of very short time intervals. The gamma decoding operation is independent of the brightness control. The only additional circuitry required to implement the brightness control in the embodiment described above is the use of a multiplier 66. The selection and synchronization signal Com; delivered by the selection and synchronization circuit 22 is, during a display phase, advantageously the same, regardless of the brightness setpoint. Consequently, the structure of the selection and synchronization circuit 22 can be simple.

[0068] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these different embodiments and variations may be combined and other variations will occur to those skilled in the art. In particular, the PWM modulation may be generated internally in the driver circuit 40 of the display pixel 1¾ to avoid using the Com signal; to generate it. Other embodiments may also use other electro-optical components such as organic light-emitting diodes.

[0069] Finally, the practical implementation of the described embodiments and variants is at the scope of the person skilled in the art from the functional indications given above.

Claims

Claims

1. A display screen (10) comprising a matrix of display pixels (12 ij) each comprising at least one light-emitting diode (LED), the display screen further comprising a first circuit (60) configured to receive initial video data (V_IN) and to apply gamma decoding to the received initial video data (V_IN) to produce gamma-corrected video data (V_G), a second circuit (62) configured to receive a brightness setpoint (B_SET), a third circuit (64) configured to provide a reduction factor (FD) which depends on the brightness setpoint (B_SET), and a fourth circuit (66) configured to multiply the gamma-corrected video data (V_G) by the reduction factor (FD) to provide brightness- and gamma-corrected video data (V_GB).

2. The display screen of claim 1, wherein the display pixels (1¾) are arranged in rows and columns, the display screen further comprising a data control circuit (24) configured to provide the video data (Dataj) to the columns of display pixels (1¾) based on the brightness and gamma corrected video data (V_GB).

3. A display screen according to claim 2, wherein each display pixel (1¾) comprises a driving circuit (40) configured to determine a digital signal (R, G, B) from the video data (Dataj) and to control the light-emitting diode (LED) based on the digital signal.

4. A display screen according to claim 3, wherein the driving circuit (40) is configured to control the light emitting diode (LED) by pulse width modulation based on the digital signal (R, G, B).

5. A display screen according to any one of claims 2 to 4, comprising a selection and synchronization circuit (24) configured to provide a succession of pulses to each row of display pixels (1¾).

6. Display screen according to claims 3 and 5, in which the driving circuit (40) is configured to turn on or off the light-emitting diode (LED) in time with the succession of pulses.

7. A method of displaying images by a display screen (10) comprising a display pixel array (1¾) each comprising at least one light-emitting diode (LED), comprising the following steps: - receiving initial video data (V_IN); - applying gamma decoding to the received initial video data (V_IN) to produce gamma-corrected video data (V_G); - receiving a brightness setpoint (B_SET); - providing a reduction factor (FD) which depends on the brightness setpoint (B_SET); - multiplying the gamma-corrected video data (V_G) by the reduction factor (FD) to provide brightness- and gamma-corrected video data (V_GB).

8. The method of claim 7, wherein the display pixels (1¾) are arranged in rows and columns, the method further comprising the step of providing the video data (Dataj) to the columns of display pixels (1¾) based on the brightness and gamma corrected video data (V_GB).

9. The method of claim 8, wherein each display pixel (1¾) comprises a driver circuit (40) configured to determine a digital signal (R, G, B) from the video data (Dataj) and to control the light-emitting diode (LED) based on the digital signal.

10. The method of claim 9, wherein the driver circuit (40) is configured to control the light emitting diode (LED) by pulse width modulation based on the digital signal (R, V,

11. nj. A method according to any one of claims 8 to 10, comprising supplying a succession of pulses to each row of display pixels (1¾).

12. Method according to claims 9 and 11, in which the driving circuit (40) is configured to turn on or off the light-emitting diode (LED) in time with the succession of pulses.

Images