WO2002071381A1

WO2002071381A1 - Method and device for obtaining a parabolic light energy curve for electroluminescent light sources displaying images on electronic projection screens

Info

Publication number: WO2002071381A1
Application number: PCT/FR2002/000738
Authority: WO
Inventors: Boris Givone
Original assignee: Boris Givone
Priority date: 2001-03-01
Filing date: 2002-03-01
Publication date: 2002-09-12
Also published as: EP1366487A1; FR2821694B1; FR2821694A1

Abstract

The invention concerns a device displaying images on a so-called light-emitting diode electronic projection screen (3), comprising a first image signal (14) generator (7), connected to a control module (5), for delivering digital signals (14) representing the light intensity of a point of the image, the control module (5) of each said diode (3) being located proximate to said diode and connected thereto by a short connection (4), the control module delivering, from the signals received from the image signal generator, a time-based cyclic ratio control signal (12, 13) of duration b divisible into time steps, and a second refreshing signal generator (9) of time interval b connected by long connection (8) to a second refreshing input of the module (5). The invention is characterised in that the refreshing signal generator (9), called second generator, is a time-based signal generator of time interval b divided into a number of time steps equal to 256, which are unequal and whereof the relative positions and duration are fixed by the refreshing signal generator. There results therefrom a parabolic progression of brightness levels. FIG. 1: 10 PRIOR ART 11 INVENTION

Description

"Method and device for obtaining a parabolic light energy curve for electroluminescent light sources displaying images on giant screens."

The present invention is in the field of electronics and relates to a method and a device making it possible to obtain a parabolic light energy curve of light sources constituted by light emitting diodes (LEDs) diffusing images, in the field of giant screens. , ie screens made up of a very large number of diodes, possibly grouped into "pixels" if it is a question of obtaining an apparent polyclomia.

It is recalled that the restitution of the luminance levels, or modulation, of an image by the light sources on a giant screen is essentially carried out by an all or nothing time control of said sources. The modulation is said to have a variable conduction duration from said sources. Generally, the time control is effected by means ^bi-of-areas of the computer and the luminance levels resulting from cutting -en not N (usually N = 256 steps) of a B timebase ( typically B - 10 milliseconds (lOmS) applied to an LED control module

This universally used modulation method has a major flaw: it. does not correctly restore the light energy power curve of the luminance levels of the images to be reproduced such that these images are determined by image generators with cyclic ratio, and this defect is reflected on the screen by a blinking of the image in areas of low light.

Indeed the curve of progression of the cyclic ratio of the temporal modulation is linear which is in contradiction with the physiology of the eye which requires a parabolic progression of the light energy.

No doubt that we have sought to address this discrepancy by correcting the image generated by the generator: it was suggested various modes of ^'correction to the Applicant's knowledge all process of changing the duty cycle, mainly modifying the frequency of the signal supplied by the generator, in particular by dividing it. This correction would require transmitting to the control module, digital signals which themselves have a fairly high frequency.

2 and make them bear an additional frequency corresponding to the correction itself, which would lead to frequencies of the order of 2,000 MHz incompatible with their passage through wired links.

Indeed, the passage of such frequencies in wired links collides with the impedance of these links, impedance itself linked to the frequency of the signal conveyed, and this effect is all the more important as the distance separating the control module. LEDs, the image generator is larger, which distance varies precisely depending on the size of the screen; in other words, the more the size of a screen increases, the more the length of the control circuits coming from the generator increases, the more their impedance increases, and the more the correction by division is ineffective.

The main idea of the invention was to parabolically modulate the duration of the steps of the refresh signal whose pseudo-frequencies, even the highest, corresponding to the shortest steps at the end of the cycle are entirely compatible with their passage. in wired connections. Consequently, a parabolic progression of the luminance levels is reconstituted without having to have them transit in digital form by the wire connections of the image signal.

Thus according to the present invention a device for displaying light images, of the type of device called "giant screens" of the type comprising a plurality of light sources consisting of light-emitting diodes assembled on a panel, a first signal generator called signal " image ", connected by long wire link to a first so-called image signal input of said control module, said generator delivering digital signals representative of the light intensity of a point in the image, a control module of each said diode located in the vicinity of said diode and connected to it by short wire link, said control module delivering, from digital signals received from the image signal generator, a duty cycle control signal having a time base of duration b divisible in steps, and a second generator of refresh signal, of time base of duration (period) equal to b, said seco nd generator being connected by long wired link to a second so-called refresh input, of said control module, is generally characterized in that the generator, said second, of refresh signal is a period time base signal generator equal to b divided into a number of steps equal to 256, steps which are not equal and whose positions and relative durations are fixed by the refresh signal generator.

3 It results from this general arrangement a distortion of the distribution of the illumination of the image with respect to the distribution that the image signal would provide if it were controlled by a time base with equal steps

Preferably, and in the case of the objective of the invention, the so-called second refresh signal generator is a basic signal generator with a time period equal to b divided into a predetermined number of steps preferably equal to 256, whose duration of the so-called first step at the end of the cycle is equal to b / 256 ² .

The duration of the successive steps of a refresh signal varies according to a quadratic or parabolic progression. Thus, the n ^{leme does} not have a duration equal to (b / 256 ² ) xn ²

In the type of device considered, the time base b having a duration of 10 mS, the first step has a duration of (10/256 ² ) xl ² mS, i.e. 0.00015 mS, the second step has a duration of (10 / 256 ² ) x2 ² mS, or 0.00061 mS 'the third step has a duration of (10/256 ² ) x3 ² mS, or 0.00137 mS „etc .. It follows from this arrangement that the levels of luminance which can have a parabolic progression suitable for good perception by the eye.

To obtain this parabolic variation of the refresh signal, those skilled in the art will have access to various means well known in the art and the choice of which will be determined by the technical context of the panel such as the use of controlled variable oscillators. in voltage (NCO) or any other digital means such as a programmed memory whose written writing bits are in parabolic progression serving to read an oscillator, without it being useful to give more details.

In a preferred embodiment the second generator is a is a voltage controlled variable oscillator (NCO). According to another embodiment, the second generator could be a programmed memory whose written write bits are in parabolic progression acting as an oscillator for reading.

The invention as defined above in terms of means or device, could, in an equivalent manner having regard to the essentially functional nature of the means of electronics, be defined in terms of image control method of a LED screen, especially large screen or

"giant screen", namely: process consisting in multiplexing at the level of the control member 4 of the LEDs, the image signal coming from a generator with a quadratic (or parabolic) signal from the cycle refresh clock of said control member, or also know: by parabolically modulating the clock signal.

Obviously, the invention relates to the screen itself as soon as it incorporates such a control device or the means implementing the method.

The present invention will be better understood and details will become apparent from the description which will be made of it in comparison with the prior art, in relation to the single figure of the appended plate. Referring to the figure, a giant screen 1 is generally divided into a plurality of modular elements such as 2 each comprising a multitude of light sources 3 (LED), each light source 3 being connected by a short wire link 4 to a module 5 control (PWM) of time data which receives on the one hand by a wired link 6 the image data of the image generator 7, and on the other hand by wired link 8 a refresh cycle frequency originating from a generator 9 clock signal.

The frequency of the image signals (14) coming from the image generator is between approximately 10 and 30 megahertz.

According to the prior art, the refresh cycle frequency of the clock signal generator 9 is fixed, that is to say that it is stable over time; such a clock signal is shown at 10, the time base of which (10 mS) is divided into constant steps, each step corresponding to an illumination or non-illumination time of the diode 3, and correspondingly in 12 the diode control signal at the output of module 5 (or at the input of LED 3). It must be understood from what has been said above that the control signal will not include an illumination or extinction duration of less than 10/256 mS, ie 0.039 mS.

On the contrary, according to the invention, the signal 13 coming from the module, or at the input of the LED 3, when it is controlled by a time base with step with parabolic variation 11, can present signals of as short duration that 10/256 ² is 0.00015 mS. This last signal duration, observed at the output of the PWM module, or at the input of the diode, or even by time photometric analysis of the illumination of the diode, is characteristic of the invention. 5 Or, typically, we will find on the screen, in the vicinity of the LEDs; or any other all-or-nothing luminescence device, on the one hand, points or terminals which will be the seat of a frequency signal of the order of 10 MHz to

30 MHz which may be the image signal 14, and on the other hand points, or terminals which will be the seat of a signal of the parabolic progression type, with a pseudo-frequency of the order of 6 MHz, which is reflected, on visual examination of the screen, by an image substantially identical to the source image.

Note also the economic interest provided by the invention by the fact that there are no additional components, but only the programming of a component, NCO for example, programming whose cost is negligible.

It should be understood that the invention is not limited to the parabolic correction of the luminance but that it can extend to the correction of any other defects linked to the structure or the components of the panels, or even to the programmed modification of illuminating images

Claims

6 CLAIMS

1.- Device for displaying light images, of the type of device called "giant screens" comprising: a plurality of light sources consisting of light-emitting diodes (3) assembled on a panel (2), a first generator (7) of signal called "image" signal (14), connected by long wire link (6) to a first so-called image signal input of a control module (5), said generator delivering digital signals (14) representative of the light intensity of a point of the image, the control module (5) of each said diode (3) located in the vicinity of said diode and connected to it by short wire connection (4), said control module delivering, from the digital signals received from the image signal generator, a control signal (12,13) with cyclic ratio having a time base of duration b divisible in steps, a generator (9), said second, of signal of refresh, time base of equal duration (period) b, said second generator being connected by long wire link (8) to a second so-called refresh input, of said control module (5), characterized: in that the generator (9), said second, of refresh signal is a basic signal generator with a period equal to b divided into a predetermined number of steps, steps which are not equal and whose positions and relative durations are fixed by the refresh signal generator from which a deformation results of the distribution of the illumination of the image with respect to the distribution that the image signal would provide if it were controlled by a time base with equal steps, and in that, more particularly, the generator (9) says second, the refresh signal is a basic signal generator with a time equal to b divided into the predetermined number of steps, the duration of the steps varying according to a parabolic progression; 7 from which it ultimately results that are restored luminance levels which may have a parabolic progression capable of good perception by the eye.

2.- Device according to claim 1, characterized: in that the predetermined number of steps is equal to 256.

3.- Device according to claims 1 and 2, characterized: in that the time base b having a duration of 10 mS, the first step has a duration of (10/256 ² ) xl ² mS, or 0.00015 mS , the second step a duration of (10/256 ² ) x2 ² mS, or 0.00061 mS 'the third step a duration of (10/256 ² ) x3 ² mS, or 0.00137 mS, etc.

4.- Device according to any one of the preceding claims, characterized: in that the generator, said second, is a is a variable voltage controlled oscillator (NCO).

5.- Device according to any one of the preceding claims, characterized: in that the generator, said second, is a programmed memory whose written write bits are in parabolic progression acting as an oscillator for reading.