A VIDEO AND LIGHTING CONTROL SYNCHRONIZING SYSTEM AND METHOD

Abstract

Described is a means for synchronizing the playback of video and lighting data, specifically to a method for conforming the timing of DMX 512 lighting data so as to coincide with video data.

Description

RELATED APPLICATION

This application claims priority of

• • PCT/US2014/61437 filed on 21 Oct. 2014; and 61/893,788 provisional application filed on 21 Oct. 2013.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to means for synchronizing the playback of video and lighting data, specifically to a method for conforming the timing of lighting data so as to coincide with video data.

BACKGROUND OF THE INVENTION

It is common in entertainment and theatrical events to use both lighting and video displays in a coordinated manner in order to present a show and to improve the experience for the audience. Video images may be provided by sources such as cameras, DVD players, media servers, hard disk recorders, computers and other similar devices. These sources may be combined and manipulated through video switchers before being output to display devices such as LED video screens, video projectors and other similar devices. The communication from the video output devices to the video displays may be through one of the standard video industry protocols including, but not limited to; DVI, SDI, HD-SDI, RGB, RGBHV, VGA, SVGA.

Lighting control at the same entertainment event may be provided by lighting controllers and may communicate with lighting equipment such as dimmer racks, automated lighting, LED lighting, and other lighting devices through a standard lighting industry protocol including, but not limited to; DMX-512, ACN, RDM, Art-Net.

A common feature of both video and lighting communication systems is that they are commonly frame based where data is sent based on a repeating time interval related to a portion of the signal or a physical characteristic of the device. For example, with video devices a frame of video relates directly to a physical frame of film in prior art technology. That is, a single static image. To achieve the illusion of a moving image multiple single static images are displayed one after the other and the human eye and brain will merge these such that we perceive a moving image. This effect is often referred to as persistence-of-vision. Depending on the format being used, single images may be shown at many different rates including 24 images per second, 25 per second, 30 per second and so on. The rate of displaying these static images is often called the frame rate of the video data. The most common frame rates used in North America are rates of 24 fps (frames per second), 30 fps, and 29.97 fps. In other areas of the world 25 fps may also commonly be used. Higher frame rates such as 48 fps and 60 fps are also utilized.

Similarly, lighting control is also often sent in a repeating manner with frames of data that are updated on a regular repeating basis. This allows lighting levels to be sent repeatedly with a different set of static levels in each lighting data frame so as to give the appearance of smooth fades or changes in lighting level. The same brain-eye persistence-of-vision phenomenon that provides this illusion in video also applies to lighting so similar data frame rates are used to obtain the smooth results desired. For example, the most common lighting data protocol in use for entertainment lighting control is USITT DMX-512A. This can support a maximum frame rate of 43 fps when 512 data values are being transmitted in each frame. In practice, many lighting controllers operate at lower data frame rates, perhaps close to the same 30 fps as is used for video.

As mentioned earlier, both video and lighting are typically used at the same time in entertainment and theatrical events. With the advent of increasing use of LED light sources both in luminaires and in video display systems the timing of these devices has become even more critical. In particular, LED and other solid state lighting devices have essentially zero rise and decay time. This is in contrast to incandescent light sources which exhibit significant rise and decay times as the physical filament heats and cools. The rapid rise and decay times of solid state lighting can make them appear to flicker and makes them susceptible to aliasing and interference effects, particularly when viewed by a frame based video camera. Different frame rates in the video and lighting systems can cause strobing, flashing and other interference effects on video systems when the video and lighting frames are out of sync or out of phase with each other. These problems may occur during, and be related to, frame by frame transitions in lighting level as well as to static levels. Prior art systems suffered from similar aliasing or phasing problems when using high intensity discharge, fluorescent, or arc lamps with film or television cameras. A solution commonly utilized in that prior art was to synchronize, or genlock, the phase of the mains supply used for the luminaires and the video frame rate. This ensured that the light output from the lamp was always active at the same points within the video frame. More recently pulse width modulated (PWM) signals used to dim LED luminaires have caused similar problems with phase aliasing on camera. These particular issues have been solved in various manners including using very high frame rates for PWM data. However, there is currently no solution for such synchronization or aliasing problems when they are caused by the competing frame rates of lighting control data and video data.

It would be advantageous to have a method of synchronizing the frame rates of lighting control data and video data in order to avoid and alleviate unwanted aliasing and interference between them.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein:

FIG. 1 illustrates a schematic diagram of an embodiment of invention synchronizing system;

FIG. 2 illustrates a timing diagram of a first embodiment of the synchronizing system;

FIG. 3 illustrates a timing diagram of a second embodiment of the synchronizing system;

FIG. 4 illustrates a timing diagram of a third embodiment of the synchronizing system; and

FIG. 5 illustrates a timing diagram of a fourth embodiment of the synchronizing system.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are illustrated in the FIGUREs, like numerals being used to refer to like and corresponding parts of the various drawings.

The present invention generally relates to means for synchronizing the playback of video and lighting data, specifically to a method for conforming the timing of lighting data so as to coincide with video data.

FIG. 1 illustrates a schematic diagram of an embodiment of the invention. Lighting control system 4 is sending DMX-512 control data 6 to lighting equipment 2 through a synchronizer 10. Similarly, video control system 5 is sending video data 7 to video display device 3. Synchronization signal 8 connects video control system 5 to synchronizer 10 so as to enable the synchronization of the lighting control data to the video data. In operation it is desirable to utilize the video signal frame rate as the master frame rate and to synchronize the lighting data to the video, rather than the other way round. Video data frames are critically timed and that timing should remain intact. Lighting data is also critically timed, however, it is possible through in this embodiment to adjust that timing and still produce a satisfactory result. Various embodiments are now discussed to achieve that synchronization and timing. All discussed example embodiments use a genlock, or frame synchronization signal, from the video data and the invention conforms the timing of a DMX-512 lighting data signal to that genlock signal. However, the invention is not so limited and other types of synchronization signal and formats of video data signal and lighting data signal may be used without departing from the scope of the invention.

FIG. 2 illustrates the timing diagram of an embodiment of the invention. The top timing trace 12 shows the genlock pulses 18 derived from a video signal and provided by the video system. The provision of genlock synchronization signals by video equipment is common as the same signal can be used to synchronize multiple components of video systems. As previously discussed, these genlock pulses may be at a 30 fps frame rate, or any other frame rate as being used by the video system. Each pulse 18a-18g relates to the start of a frame of the video signal. The center timing trace 14 shows the raw DMX 512 lighting data frames as generated by the lighting control desk and input to the synchronizer. In the example illustrated the input DMX 512 frame rate is higher than that of the video genlock signal, thus there are more DMX 512 frames than video frames. In order to constrain the lighting DMX 512 data to the frame rate of the video genlock signal the number of DMX 512 frames has to be reduced in some manner.

In the embodiment illustrated in FIG. 2 this data reduction is achieved by discarding some of the DMX 512 data frames and delaying others. As illustrated frame 1 of the DMX 512 data 14 is passed through as coinciding with the first pulse 18a of genlock signal 12. The DMX 512 data now passes into a buffer within the synchronizer of the invention. This buffer accumulates a single pending DMX 512 data frame and awaits the arrival of the next genlock pulse 18 before releasing that frame. Thus, frame 2 is accumulated in the buffer and is output on receipt of the next genlock pulse 18b. DMX 512 frame 3 is next accumulated within the buffer, however DMX 512 frame 4 arrives before the next genlock pulse 18c is seen. Thus, the buffer discards frame 3 and instead, accumulates frame 4. Frame 4 is then output on receipt of the next genlock pulse 18c. The system proceeds in this manner and outputs DMX 512 frames 1, 2, 4, 6, 8, 9, and 11 synchronized with genlock pulses 18a-18g. DMX 512 frames 3, 5, 7, and, 10 are discarded.

The situation illustrated in FIG. 2 where the DMX 512 frame rate is greater than that of the video genlock signal is the more common in practice, however, if instead the DMX 512 frame rate was lower than that of the video genlock signal, the invention is still operative. Under these conditions, the DMX 512 frames may be repeated from the buffer within the synchronizer in order to create the necessary extra DMX 512 data frames.

FIG. 3 illustrates a timing diagram of a second embodiment of the invention. The timing diagram presents the same situation as FIG. 1 where the DMX 512 frame rate is greater than that of the video genlock signal. In this embodiment the data reduction is achieved through the combination and interpolation of DMX 512 data frames instead of discarding frames. The process is similar to that described in FIG. 2. As illustrated in FIG. 3, frame 1 of the DMX 512 data 14 is passed through as coinciding with the first pulse 18a of genlock signal 12. The DMX 512 data now passes into a buffer within the synchronizer of the invention. This buffer differs from that described in the first embodiment in that it accumulates multiple pending DMX 512 data frames awaiting the arrival of the next genlock pulse 18. Thus, frame 2 is accumulated in the buffer and is output on receipt of the next genlock pulse 18b. DMX 512 frame 3 is next accumulated within the buffer, however frame 4 arrives before the next genlock pulse is seen. Thus, the buffer additionally accumulates frame 4 and creates a new, interpolated, frame from the data contained in both frame 3 and frame 4. The newly created interpolated frame is then output on receipt of the next genlock pulse 18c. The system proceeds in this manner and outputs DMX 512 frames 1, 2, 3+4, 5+6, 7+8, 9, and 10+11 synchronized with genlock pulses 18a-18g. The ‘+’ symbol in this case indicates a combination and/or interpolation of the relevant frames. Such combination and interpolation may proceed in a pre-determined manner that may differ with different lighting instruments. For example, a simple averaged value for each lighting channel may be appropriate for lighting intensity information, while a more complex combination algorithm may be needed for color, position, or other lighting related data. The invention may provide any interpolation or combination algorithms as appropriate. While the example shows interpolation of two frames in other embodiments there may be more or less frames that require interpolation depending on how many DMX 512 frames occur between any two video frames. In some embodiments the number frames may be consistent in other embodiments the number of frames to be interpolated may not be consistent.

FIG. 4 illustrates a timing diagram of a third embodiment of the invention. The timing diagram presents the same situation as FIG. 1 where the DMX 512 frame rate is greater than that of the video genlock signal. In this embodiment the data reduction is achieved through the full processing and re-timing of DMX 512 data frames instead of either discarding frames or performing simple interpolation/ combination on two frames at a time. This embodiment is more complex than those illustrated in FIGS. 2 and 3, the synchronizer of the invention may decode the DMX 512 data and re-generate it 22 using the genlock pulses 18a-18g as a timing reference. The synchronizer may be configured to have knowledge of the types of lighting instruments connected to the DMX 512 data stream, and will re-generate data accordingly. In the example illustrated DMX 512 frames 1 to 12 are processed and re-timed to be output as DMX 512 frames 23a-23g to correspond with genlock pulses 18a-18g.

FIG. 5 illustrates a timing diagram for a fourth embodiment of the invention. In this embodiment the synchronizer of the invention has been incorporated within the lighting control system directly. This may be represented as hardware and/or software within, for example, a lighting control desk, media server or intelligent lighting node 24. Synchronization of the DMX 512 output to the genlock signal 12 may now happen before any DMX 512 signal is generated. The lighting control system itself will generate DMX 512 lighting frames 25a-25g using the genlock pulses 18a-18g as the timing reference.

In yet further embodiments of the invention the described synchronization technique can be applied to multiple separate data streams of DMX 512. (Different data streams of DMX 512 are often referred to as universes). If each data stream/universe is independently and individually synchronized to the same video signal then the DMX 512 data streams will also be synchronized with each other. The use of multiple DMX 512 data streams in a single large show is commonplace and, with the advent of fast reacting LED based luminaires, timing differences between the different DMX 512 data streams can be apparent to the viewers, with slight delays showing up between the lighting changes on one part of a stage compared to another art of the same stage that is running a separate DMX 512 data stream. If all data streams originate from the same lighting control console then some of this synchronization can happen within that consoled, however if, as is becoming common, there are multiple lighting controllers, nodes, computers and other devices generating DMX 512 data streams then there is no existing means to synchronize those data streams.

In this disclosure the invention the synchronizing signal has been described as originating from a video signal. This is because the synchronizing with video is one of the primary drivers for the need for the invention. However, the invention is not so limited and other signals could be used as the synchronizing source. For example, synchronization timing could be derived from a master DMX 512 data stream, from time code (such as SMPTE VITC) embedded in video, audio or lighting signals, from the mains power signal, from time code derived from Ethernet or other networking protocols, from Artnet, ACN, RDM or any other time code or heart-beat signal that are well known in the art.

Although this disclosure has discussed the invention in particular exemplary embodiments, the invention is not so limited and further embodiments of the invention may achieve comparable results where the lighting data frame is synchronized to the video data frame.

While the disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as disclosed herein. The disclosure has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the disclosure.

Claims

1. A lighting control system comprising:

a light emitting device that utilizes a frame based video signal;

a timed control signal for controlling light output; and

a synchronizer that synchronizes the timing of the control signals output to the frame rate of the video signal.

2. The lighting control system of claim 1 further comprising:

a second timed control signal for controlling light output and the synchronizer synchronizes the timing of the second timed control signal with the first timed control signal to the frame rate of the video signal.

3. The lighting control system of claim 1 where time timed control signal for controlling light output is a plurality of timed control signals and all of the plurality are synchronized with the frame rate of the video signal.

4. A DMX 512 lighting control system further with a synchronizer for receiving a synchronizing signal and synchronizing the DMX output(s) to synchronized in accordance with the synchronizing signal.