DE4132853C2 - Method and device for avoiding the flickering of brightness of a video image reflected from a film camera - Google Patents

Description

The invention relates to a method for avoiding light flickering of the video image on the beam path a film camera with a mirror lens or another periodically interrupted optical beam directed Video camera with a video sensor and a device for Implementation of such a procedure.

Video cameras for SLR cameras to record the Viewfinder images have been used for many years. From the DE 35 25 526 C1 it is known to have a motion picture film camera rotating mirror cover with a magnifier extension to provide and a mirror for a video camera in to order this magnifier extension. In the viewfinder Beam path of the SLR motion picture film camera is located  itself a beam splitter, so that the viewfinder image also one Video camera is fed, which accordingly as a video viewfinder camera can be called. The video camera gets that Image as well as the viewfinder alternate with the film. While the exposure time of the film remains the image sensor of the Video camera unexposed. Only during that time while the mirror cover covers the film receives the Video camera take a picture. This will drop depending on the film speed of the rotating mirrors aperture, especially for non-synchronous operation between Film camera and video camera, image sections. this leads to especially with fast solid-state image recorders (half conductor sensors, CCD's) to flickering, the one Image assessment significantly complicate and record to make impossible. For video cameras with recording tubes this effect also exists, but falls due to the Inertia of the photocathode less pronounced.

To avoid or reduce these flickering the following suggestions are already known:

It is possible to synchronize the film camera to the video camera sieren. The video camera has a frequency transmitter that specifies a frequency of 50 or 60 Hz, for example. By synchronization can be achieved that both the Film camera as well as the video camera synchronized to a pre given frequency, for example the network frequency. It another frequency can also be specified. This The procedure is only for fixed frame rates by the Video standards are specified, suitable. If the picture is different frequencies, the image dropout is not eliminated. It was proposed, in addition, a special mirror cover watch for the exposure of each video field. This too is however only possible for fixed frame rates of the video camera. The image dropout is fixed. However, it will the recording light for the film camera is significantly reduced.  

In addition, expensive special film cameras (e-cam) are required derlich, which are no longer for normal mobile operation are suitable, but only for use in studios.

It is known from DE 34 37 210 A1 to record partial images draw and save line by line in the video clock. Then the drawing files become full pictures line by line added. This process is very complex electronically. It are large special film cameras with precise synchronization facilities required. For these reasons, this is System known as "WAVE" disappeared from the market again.

From DE 38 33 823 C1 a method is known in which Drawing files can be scanned. The speed and position or phase of the revolving mirror diaphragm and the Integration window of each individual video field detected. This results in the exposure time of the semiconductor sensor determined, that is the duration of the true exposure of the half conductor sensor. The integration window indicates the location and size of the integration interval for each field of the Semiconductor sensor. While the size of the integration window a norm-specific or camera-specific matter is, the location of the integration window from the synchronous signal of the video signal can be derived. Since the synchron signal is specified, you can in relation to the synchronous signal the start of the integration time of the semiconductor sensor deduce. To reduce the flickering of brightness, that is Video output signal of each video field with one Correction factor multiplied. This correction factor is a function of the ratio of the average exposure time of a video field at true exposure time this Video field. This true exposure time depends again of the speed and phase of the mirror diaphragm and the Integration window of the video image. The correction factor can be determined using a function table preferably after the gamma correction curve of the video camera.  

The drawing files are not saved. The video amplifier kung is inversely proportional to the percentage Exposure of the respective video image via a computer and an electronic table (EPROM, PROM) for consideration the phase and frequency ratio between video and Film camera. The method known from DE 38 33 823 C1 however, has a number of disadvantages. A correction is only possible within narrow speed limits. Missing Parts of the picture cannot be added. The signal-to-noise Ratio deteriorates significantly because of the noise reduced signal is fully amplified. It is one specially equipped film camera required. It will only produces a limited flicker-free image.  

US 4,928,171 discloses a video camera for a single-lens reflex camera, at which the image scan created is implemented on a common television standard.

From US 4,839,729 a CCD sensor is known in which the integrated Single images are buffered in a buffer.

DE 35 17 737 A1 describes a method for recording and Playback of static or moving objects known, in which by means of an up and took individual pictures of the object in the standard cycle Single images in succession on a playback device or a Zwi be given memory. Electric charges become dependent integrated in the brightness of the object image. At below a pre Given the threshold of charge quantities, the reading process for a predetermined number of standard cycles suspended.

EP 0 162 311 A2 discloses a control circuit for a tube video Camera and a method for controlling this tube camera, in which a La image of an object to be recorded is generated when reading out the charge image for generating a video output signal of the video camera is at least partially deleted. To even with fluctuating, especially pe periodically interrupted light supply from the object to be recorded to the video To generate a flicker-free video image from the camera, the control circuit has one Signal source whose output signal is the presence and absence of a light represents supply from the object to be recorded to the video camera. The tax circuit is connected to the input of the tube camera. She leads the sem a signal preventing the reading of the charge image at least during the length of time during which the output signal of the signal source is present represents the supply of light. A disadvantage of this method is that the clock  of the video frame must be shorter than the dark period, otherwise the procedure ren is not feasible.  

The object of the invention is the significant restrictions to avoid the known methods just described.

According to the invention, this object is characterized by the solved the part of claim 1 specified features. The on light-dark phases (exposure intervals) are recorded. This becomes a trigger signal derived the beginning of the integration of a single image controls on the video sensor. The method according to the invention is suitable for a motion picture film camera with a rotate the mirror cover. But it is also for other SLR suitable cameras with fixed or variable image sequence as well for other video recordings with intermittent breaks exposure, the interruption being regular or can be irregular. In general, that describes Method according to the invention a video camera system for synchronous capture of the viewfinder image from SLR cameras with fixed or variable image sequences or otherwise eng video recordings with regular or irregular under broken exposure without flickering. With the inventive methods are during image recording with a single-lens reflex camera (freeze frame or motion picture)  synchronous to this via the viewfinder channel of the camera video images recorded and with a fixed image sequence according to video standard reproduced without flickering. The video output signal is in black and white or color according to the internals national standards possible.

The light-dark phases occurring on the video sensor or Exposure intervals are recorded, both after Phase position as well as according to interval length. this happens preferably by a brightness detector that the incident light intensity and from this the brightness Detects dark phases of the (rotating) mirror diaphragm. Out the exposure time of a individual video image derived. The detection of the light Dark phases can also be done differently, for example by detecting the position of the mirror aperture of the film camera.

With short exposure times (this corresponds to high image can follow) several, for example two or more, Bright phases are collected in the video sensor. Hereby the video sensor receives a multiple of light per up taken film picture, resulting in an even higher video picture Quality leads.

Advantageous further developments are in the dependent claims wrote.

The individual images integrated in the video sensor can be Film camera-controlled caching controlled by Video frames in a preferably digital image memory be taken over. It is advantageous if the in the video sensor-integrated single images in a buffer be cached. The cache can Storage zone of the video sensor. Preferably the individual images stored in the image memory continuously  output, advantageously in video standard or corresponding to a frequency of the video standard.

The light falling on the video sensor can be during or the bright phases of the video sensor. After this At the end of the (last) light phase, the charges of the Video sensors are taken over in its storage zone. Of there they will B. when the next video Frame read out. This is done through a sequential control system controlled. If a new light phase occurs during this reading occurs, this does not bother, since it is now in the light phase charges formed in the image sensors be saved and not yet adopted.

The (read out) video images can be recorded in a video preparation level. The (reinforced) Video images can be written into an image memory become. This image memory is preferably a digital one Image storage. He can get a quick one at his entrance Analog-digital converters have and one at its output fast digital-to-analog converter. The image memory saves the valid pictures and gives them continuously at the exit Video standard off until a new picture is available.

An inventive device for performing the inventions The method according to the invention consists of a periodically under broken optical beam path, preferably one Film camera with a mirror aperture, a video sensor, one Detector, preferably a brightness detector, for detection the light-dark phases occurring on the video sensor (Exposure intervals) and a control device for Trigger the integration of the impact on the video sensor the light through the detected light-dark phases. The Brightness detector is preferably located next to the Video sensor or in addition to the optics that the video sensor is arranged, or in the associated beam path or one of them  split beam, especially using the IR Proportion of radiation.

The control device is a set-up device, which is the signal of the detector or brightness detector on the one hand and the video frame on the other hand processed for Triggering the image acquisition, to take over the in the video sensor integrated single images in the buffer, for Transfer of the individual images into the image memory and for off reading the image memory.

An advantageous development of the device according to the invention device is characterized by a sequence control for the transfer taking the charges of the video sensor after the end of (last) bright phase in the memory zone of the video sensor and / or for reading out the content of the memory zone of the Video sensor when the z. B. next after Takeover of video frames occurring in the storage zone and / or for inscribing the (amplified) video images in a preferably digital image memory and / or to continue continuous output of the stored images to the image memory Output.

Another advantageous development is characterized through a video editing stage to reinforce the (read) video images and standard complements the Image signals.

An embodiment of the invention is described below described in detail in the accompanying drawing. In the Drawing shows

Fig. 1 is a motion picture film camera with a rotating mirror shutter, a finder optical system and a video camera in a schematic representation,

FIG. 2 shows a view of the motion picture film camera of Figure 1 in the direction X at a time in which the film is exposed.

Fig. 3: the motion picture film camera shown in Figure 2 in a time in which the detector and the video camera are exposed.

Fig. 4 shows a first block diagram,

FIG. 5 shows a second block diagram,

Fig. 6: the time course of the video frame (top) and the brightness detector (bottom) and

Fig. 7: another representation of the temporal course of the video frame and the brightness detector for three different film camera frame rates.

The motion picture film camera shown in FIG. 1 has a mirror diaphragm 1 which rotates about an axis 2 . The light of the object to be recorded passes through the lens 3 to the mirror diaphragm 1 or - depending on its position - to the film 4 located behind it. When the mirror diaphragm 1 is in the position shown in FIG. 2, the film 4 is exposed. If the mirror aperture 1 is in the position shown in Fig. 3, the light from the mirror aperture 1 is deflected at right angles. From there it arrives in the finder beam path 5 , in which a beam splitter 6 is located. The deflected partial beam 7 passes through the eyepiece 8 of the viewfinder into the eye of the cameraman, the continuous partial beam 9 reaches the video camera 10 . A video sensor (for example a CCD) is arranged within the video camera 10 . A focusing screen 11 may be located in the beam path 5 at the location of the viewfinder image.

Brightness detectors 12 are arranged on the input side of the video camera 10 in the vicinity of the input optics of the video camera. These brightness detectors 12 detect the incident light intensity and use them to identify the light-dark phases of the rotating mirror diaphragm 1 . However, it is also possible to detect the light-dark phases of the rotating mirror diaphragm from the angular position of this mirror diaphragm. The exposure time of a single video image is derived directly from the light-dark information.

There is no sense for image sequences between 0-10 frames / sec full evaluation. If less than 10 frames per second the video camera should be made with its standard frequency of 50 or 60 Hz run freely, as an infinite Exposure time is not possible. To this special case too will recognize at frame rates around 5 frames per second made a decision. In order to avoid disturbances (e.g. at a pan of the camera over very dark objects) none Incorrect switchover between the two operating states "free-running camera" and "more than 10 frames per second" too is obtained between these two states as follows switched:

If the camera is in its static state (0 pictures per second), it is checked whether during a second there are at least 8 light-dark transitions. If this is the If this is the case, the system changes to the other state. Otherwise the camera remains in its static state. If the camera is in its dynamic state (more than 10 Frames per second), it is checked whether a light-dark over gear is greater than 200 ms. This corresponds to an image frequency of less than 5 frames per second. If this is the If so, it is checked for a second whether more than 8  Light-dark transitions have occurred. If so, too the camera remains in its dynamic state. Otherwise the system switches to the static state. in the The end result is a certain hysteresis.

With the exposure intervals obtained in this way, the exposure control of the CCD sensor is controlled by the sequence control. As can be seen from FIG. 4, there is a brightness detector A (reference number 12 in FIG. 1) which emits a trigger signal. The brightness detector A outputs signals to the sequential control unit D. The CCD recording sensor B outputs signals to the video processing unit C. Furthermore, the CCD recording sensor B exchanges signals with the sequence controller D. The video processing system C also exchanges signals with the sequential control system D. The video processing unit C also outputs signals to the digital image memory E. This digital image memory E exchanges signals with the sequence controller D. The transition from the viewfinder beam coming light is denoted by 1, the video output is designated in FIG. 4 with 2.

The CCD image sensor B has image sensors and a closed storage zone. Furthermore, the CCD image sensor B can be operated in the “delete”, “take over” and “read out” operating modes. With these inputs, delete, accept and read out, the exposure time can be varied and reading can be started at the right time. The flow chart in Fig. 6 describes this procedure. The video signal (the video signal frame) is shown there, which consists of continuously repeated signals. Below this, the light-dark information is given. If the signal level of the light-dark information is at "1", this means that the video camera is not receiving any light. When light strikes the video camera, the signal level of the light-dark information is at "0".

At time 1 (cf. lower curve in FIG. 6) during the dark phase, the sensor H is constantly deleted by the control input. The deletion is stopped from time 2 and the incident light is collected in the image sensors of the CCD image sensor B. When state 3 is reached , all charges are taken over by the image sensors into the storage zone of the CCD recording sensor B. The sequence control D now waits until the next video frame (cf. upper curve in FIG. 6) and reads out the individual pixels from the memory zone of the CCD sensor B at the time in which the next video frame occurs. So this happens at time 4 . This process lasts until time 5 . If a new bright phase occurs during this time, this is not a problem since the charges now occurring are initially stored in the image sensors of the CCD recording sensor B and have not yet been accepted. In the case of very high image sequences, the sequence control D must decide whether there is "good" information or whether a new exposure has to be started if necessary.

The sporadically occurring images are amplified in a video processing stage C and written into the digital image memory E. The image memory E has a fast analog-to-digital converter, for example operating at 15 MHz, followed by a memory with, for example, 256 K × 8 bits, and a fast, for example operating at 15 MHz digital-analog converter at the output. It stores the valid images between states 4 and 5 (cf. lower curve in FIG. 6) and outputs them continuously at the output until a new image is available.

With higher image sequences (i.e. with short exposure times), you can increase the sensitivity by using several Bright phases in the image sensors of the CCD image sensor B collects before you take them into the storage zones. The Control for this is taken over by sequence control B.  

This ensures a flicker-free video image.

With the invention it is possible, even with variable Exposure times to get a flicker-free video image. Exposure times can vary from 200 ms to 2 ms (This corresponds to a frame rate of 5-500 frames per Second). Other exposure times are without essential Changes possible due to changes in individual parameters. The invention is almost without any electrical intervention Film camera or other optical transmission device adaptable. An increase in sensitivity by one selectable factor preferably between 2 and 16, but also is higher by adding the amount of light of several images Film camera or exposure phases of any optical Operation adjustable from the outside.

Automatic recording of images from 0-500 images per Second, controlled by the process to be recorded, is after Some parameters can be changed. It is automatic Detection provided for period periods (exposure times) of more than 200 ms (less than 5 frames per Second) in a normal video recording mode (at 50 Hz or 60 Hz).

FIG. 7 shows the time profile of the light distribution 32 on the video sensor or film and the video frame 37 . In Fig. 7A, the relationships with a film camera frame rate of 25 frames per second are shown. The frequency of the video frame is also 25 frames per second or 50 fields per second. The complete cycles of the mirror aperture are numbered in line 31 . With each full rotation of the mirror diaphragm, the viewfinder and the video camera are exposed during one half 41 of the time, and the film is exposed during the other half 42 of the time. This light distribution is shown in line 32 . During the exposure time 41 of the video camera, the light falling on the video sensor is integrated, as shown in line 33 . At the time 43 of the end of the exposure time of the video sensor, the integrated image from the video sensor is transferred to the buffer, as shown in line 34 . From this point in time, the buffered image is available for reading out. However, it is only read out at the point in time 44 in which the next video frame appears. At this point in time 44 , the transfer 36 of the temporarily stored image takes place.

As a result, the images of the CCD image sensor film camera synchronous ( 33 ) are time-corrected ( 35 ) in a video memory in a digital memory ( 36 ), from which they can be called up as often as required via an intermediate memory ( 34 ).

In the case of the same frame rate ( FIG. 7A) of the film camera (25 frames per second) and the video signal (25 frames per second or 50 fields per second), each viewfinder image recorded is reproduced twice, namely once for the viewfinder phase 41 , on the other hand for the film exposure phase 42 .

If the frame rate of the film camera is lower ( FIG. 7B: 22 frames per second) than the video standard (25 frames per second), from time to time a “field” is not called up twice, but three times from the memory 36 .

If the frame rate of the film camera is higher ( Fig. 7C: 28 frames per second) than the video standard, a field must occasionally be omitted because of the "oversupply" of images.

In this described type of "time-variable" intermediate storage ( 35 ), an image-frequency stable, standardized FBAS video output signal ( 37 ) arises at any film camera image frequency. The entire process is done in digital video signal processing.

Claims (14)

1. A method for avoiding the flickering of brightness of the video image of a video camera with a video sensor directed at the beam path of a film camera with a mirror diaphragm or another periodically interrupted optical beam path, characterized in that
that the video sensor is a CCD sensor
that the light-dark phases (exposure intervals) occurring on the CCD sensor are detected
and that the integration of the light striking the CCD sensor is triggered by the detected light-dark phases. 2. The method according to claim 1, characterized in that the in the CCD Sensor integrated frames in a buffer, preferably the storage zone of the CCD sensor. 3. The method according to claim 1 or 2, characterized in that the individual Images controlled from the video frame into a preferably digital image file cher be taken over. 4. The method according to any one of the preceding claims, characterized records that the one stored in the buffer or image memory  Single images are output continuously, preferably according to a video standard become. 5. The method according to any one of the preceding claims, characterized shows that with short exposure times, several bright phases in the CCD Sensor can be collected. 6. The method according to any one of the preceding claims, characterized records that with long exposure times the CCD sensor with its Stan dard frequency is read out. 7. The method according to claim 6, characterized in that the switching of the CCD sensor between camera-synchronous reading and its standard tard frequency with a certain hysteresis. 8. The method according to any one of the preceding claims, characterized records that the light-dark phases of a brightness detector can be detected. 9. The method according to any one of the preceding claims, characterized records that the charges of the CCD sensor after the end of the (last) Bright phase are transferred to the buffer. 10. The method according to claim 9, characterized in that the content of the Zwi storage when the next occurs after the transfer to the Intermediate memory occurring video frame read out or in the image memory is taken over. 11. The method according to any one of the preceding claims, characterized records that the (read) video images in a video Preparation level reinforced and supplemented in accordance with standards.   12. Device for performing the method according to one of claims 1 to 11, consisting of
a periodically interrupted optical beam path, preferably a film camera with a mirror diaphragm,
a CCD sensor,
a detector, preferably a brightness detector for detecting the light-dark phases (exposure intervals) occurring on the CCD sensor and a control device for triggering the integration of the light incident on the CCD sensor by the detected light-dark phases. 13. The apparatus according to claim 12, characterized by a sequence control to take charge of the CCD sensor preferably after End of the (last) light phase in a buffer, preferably the Storage zone of the CCD sensor and / or for reading out the content of the intermediate memory or the storage zone of the CCD sensor when an egg occurs nes, preferably the next after the takeover in the clipboard cher or the memory zone occurring video frame and / or for on write the (amplified) video images into a preferably digital image memory and / or for the continuous output of the possibly saved saved images at the image memory output. 14. The apparatus according to claim 12 or 13, characterized by a video Preparation level for strengthening and / or completing the standards (read out) video images.