FR2461417A1 - COLOR TELEVISION CAMERA - Google Patents

Abstract

COLOR TELEVISION CAMERA. B. CAMERA CHARACTERIZED IN THAT IT INCLUDES A 6R, 6B MIXER FOR RY, BY COLOR DIFFERENCE SIGNALS AND A Y CORRECTION SIGNAL, AN ADJUSTABLE GAIN CONTROL 11B FOR THIS SIGNAL, 13 SAMPLING MEANS AND A CONVERTER OF A REFERENCE SIGNAL AND A SAMPLE COLOR DIFFERENCE SIGNAL, AS WELL AS A 33 MEMORY TO RECEIVE MRF REFERENCE AND SEA DIFFERENCE SIGNALS AS WELL AS A MEAN 16, 17, 30 TO MODIFY THE SIGNAL OF SAMPLE COLOR DIFFERENCE AND A MEAN 18 GIVING A GAIN CONTROL SIGNAL. C. THE INVENTION APPLIES TO COLOR VIDEO CAMERAS.

Description

The present invention relates to a television camera

  color vision comprising means for adjusting the balance of the video signal and in particular a simple means comprising a microcomputer. A method for adjusting the white balance is known (FIG. 1). According to Figure 1, the image of the object 1 is projected through the lens 2 of the tube 3 of the camera; horizontal and vertical synchronization signals of the synchronization signal generator 4 are applied to the tube 3 of the camera to give a video signal. This video signal passes through a decoder 5 which gives color difference signals RY, BY and a luminance signal Y. The color difference signals RY, B-Y drive the mixers 6R, 6B whose outputs are applied to window comparators 7R, 7B. The comparators 7R, 7B have VTL and VTH thresholds which are respectively set at a predetermined level below and above a reference level of the video signal in the erase period. The comparators 7R, 7B thus give a signal that the input signal level is outside the range between the thresholds and a signal indicating whether the input signal level is above or below or below the

  range defined by the thresholds. The signals of each of the

  7R, 7B are applied to counting and counting / counting control terminals for each of the up / down counters 8R, 8B. When the color difference signals R-Y, B-Y have a level higher than the threshold VTH, the counters 8R, 8B work in down counting whereas if the signals are lower than the VTL threshold, the counters 8R, 8B work in counting. The counters 8R, 8B receive a cadence signal from a clock generator 9. The state of the counters 8R, 8B is applied to digital / analog converters (D / A) 1OR, 10B which give DC voltages proportional to the current. amplitude of the counting states. These DC voltages are passed through gain control circuits 11R, 11B which allow luminance signals Y to pass through.

by the mixers 6R, 6B.

  In this way, when the signals of different

  R-Y, B-Y color difference is outside the range between the VTH, VTL thresholds, the gain control circuit liR, llB is controlled to adjust the signal level

  luminance + ^ Yr, + AYb applied to the mixers 6R, 6B.

  It is thus possible to adjust the R-Y color difference signals,

  B-Y in the range between the thresholds VTH 'VTL-

  However, in this known arrangement, since the thresholds VTH 'VTL are defined by a circuit other than that of the color difference signals, there is a risk of an offset error between these circuits and this error increases as a function of the constants of the circuit, during time etc. In addition, since the up / down counters 8R, 8B count bit by bit, it is necessary to

  a lot of time to correct an input error, important.

  The present invention aims to remedy

  disadvantages of the known solutions in tele-

  white-balance vision by detecting a white object (subject) and adjusting the level of the luminance signal Y of the color difference signals so that the color difference signals RY, BY are of the same level as the video signal of the erase period. In other words,

  the invention proposes to create a television camera

  carrying a means of adjusting the balance of white to

  using a simple device with a microprocessor.

  According to the invention, the reference level (or the video signal level of the erase signal interval) used for the adjustment of the white balance and the level of the error signal of the period of the signal in which white balance can be adjusted (or the level of the RY signal) are calculated by the same signal processing system so as to have a television camera having no adjustment error of the white balance as a result of the

  dispersion or drift of the constants of the circuit.

  Correction of the white balance adjustment must be done very quickly and the system must work first to make a rough adjustment, then a fine adjustment, so as to reduce the time required to adjust

  performed according to known techniques.

  Since the time required to adjust the balance is short, the camera's vibrations during shooting

  have little influence (shooting on a white board or

  logue), which results in a correct adjustment of the equilibrium

of white.

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  According to another characteristic, the invention relates to a means for regulating the balance of the white in a

  color video camera, using a microprocessor

  a read-only memory, a random access memory and a central processing unit as well as data buses (lines), this camera comprising: a) sampling means or providing a reference video signal (VRF) in the interval d an input video signal

  while the camera provides signals from a single object

  chromium, b) an analog / digital converter of the reference signal sampled to give a digital reference signal, c) means for recording in memory the digital reference signal in a first region of the RAM,

  d) a means for sampling the difference signal of

  in the video scanning interval of the input video signal, e) an analogue / digital conversion means of the color difference signal into a digital color difference signal, f) an in-memory recording means a digital color difference signal in a second region of the RAM memory; g) a means for calibrating or substituting the content of the digital color difference signal stored in memory so as to coincide with the difference signal contents; of color, digital recorded in the second region of the memory, the contents of the digital reference signal being recorded in the first region of the memory, h) means for adjusting the level of the luminance signal to be mixed with the difference signal color based

  substituted content in the second memory region.

  The present invention will be described in more detail with the aid of the accompanying drawings, in which: FIG. 1 is a block diagram of a known system

  adjusting the white balance.

  FIG. 2 is a block diagram serving to explain

  the operation of the embodiment according to the invention.

  - Figures 3 and 4 are explanatory diagrams for explaining the operation of the embodiment of the invention.

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  DESCRIPTION OF A PREFERENTIAL EMBODIMENT

  Figure 2 shows an example of a montage of

  the invention; in this figure, the same references have been used.

  than in Figure 1 to designate the same elements. -

  A microcomputer 30 includes a central processing unit (CPU) 31, a read only memory (ROM) 32 in which a program to be executed by the CPU 31 is written, a random access memory (RAM) 33 for storing the data, a input / output circuit 34 etc. In this computer, the CPU 31, the ROM 32 and the RAM 33 are connected by an address bus 35, a data bus 36 and a control bus 37; the CPU 31 and the input / output circuit 34 are

  connected by the data bus 36 and the control bus 37.

  This microcomputer 30 and the components mentioned are made in the form of a large-scale integration circuit (LSI) made on the same large chip. The signals of the mixers 6R, 6B are applied to two fixed contacts of a switch 12 which is implemented by a signal provided by the microcomputer 30 to select one of the signals and apply it to a sampling circuit and to 13. The signal of the synchronization generator 4 is applied to a pulse generator

  sample 14, which then gives impulses for

  SPl 'Sp2 (curves of Figures 3B and 3C) corresponding to

  during the erasure period, TB and the video scan period, Tp for the input video signal Vin (FIG. 3A). The

  Spi 'Sp2 sampling pulses are applied respectively

  two fixed contacts of an inverter switch 15

  which is implemented by a signal provided by the microcalcula-

  30 to choose one of the sampling signals and the

  provide sampling and holding circuit 13.

  The sampling and holding circuit 13

  gives a signal and applies it to the (+) terminal of the comparator 16.

  In addition, the content located at a given address of the memory 33 of the computer 30 is applied to a digital / analog converter (D / A) 17 which transforms it into an analog signal:

  the analog signal is then applied to the (-) terminal of the

  16. The comparator 16 gives an output signal and applies it to the computer 30. The content at a given address

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  the memory 33 of the computer 30 is applied to the sampling and holding circuits 18R, 18B by the D / A converter 17; the sampling pulses of the computer 30 are applied to the sampling and holding circuits 18R, 18B which respectively give the voltages Vcl 'Vc2 corresponding to the contents of the given addresses. The voltages Vc1 'Vc2 are applied to the gain control circuits 1R, 1EB. The synchronization signal of the synchronization signal generator 4 is also applied to the computer 30. In addition, the computer 30 receives the signal from the manual switch 19 to start the adjustment of the white balance and provides an error indicating signal etc to a device or element

indicator 20.

  The ROM ROM 32 contains a program that

  will be described using the table in Figure 4. In this

  gram, the R-Y color difference signal is first

  set, and then adjust the B-Y color difference signal.

  According to the flowchart of FIG. 4, the execution of the program is started and in step 1 of the program it is decided whether the switch 19 is closed or not. If the switch 19 is open, repeat step 1. When the switch 19 is closed,

  the program goes to step 2 which performs self-balancing

  whiteness, that is to say that in step 2, the switch 12 is put in the connection position of the mixer 6R of the

  R-Y color difference signal.

  Then, in step 3, the computer 30 gives a digital signal, for example "80" (the number in quotation marks corresponds to a decimal value) for adjusting the gain control circuit 1R on a reference gain and provides this signal through the converter D / A 17 to the circuit

  sampling and holding 18R.

  In step 4, the switch 15 is put in the position in which there is a sampling pulse

  corresponding to the erasure period.

  Then, in step 5, the sampled and maintained level of the signal is stored in the computer 30 at a first storage address. In this case, the MRF content of the first storage address is read and is supplied through the D / A converter 17 to the comparator 16 terminal (-) which sequentially compares this signal with the level that is applied to its terminal. (+>, the MRF content of the first storage address is thus modified sequentially until the inputs of the comparator 16 are equal to each other.Therefore, the content MRF stored at the first address finally coincides with the value retained in the exchange

Tilling and Retention 18.

  During step 6, the switch 15 is put in

  a position giving the corresponding sampling pulse

  during the video scan period.

  Then, in step 7, the level of the signal sampled and kept by the circuit 13 is recorded at one second

  storage address in the computer 30.

  Accordingly, during the erase period, at the first address of the RAM 33 of the computer 30, the video signal level and the video signal level of the video scanning period are recorded at the first address of the computer 30.

the second address.

  In step 8, the difference contained in MER is calculated

  at the second address - MRF content at the first address.

  In step 9, the MER content of the second address is replaced by "80" minus the result of the calculation; in this case, if the remainder or result of the calculation is positive, the number "80" is reduced by the difference; on the other hand, if the rest

  is negative, the number "80" is increased by this difference.

  Therefore, the content at the second address is practically

  equal to that of the first address.

  Then, in step 10, the computer 30 supplies the content MER of the second address to the sampling and holding circuit 18R via the D / A converter.

to be preserved.

  In the sampling and holding circuit 18R, a potential is fixed which is corrected by the calculation result mentioned above and thus the level of the color difference signal RY is made close to the level in the erase period with the setting A Yr. The VER level (curve of Figure 3A) is approximately equal to VFR. In this way, the level in the erase period is substantially equal to the level of the RY color difference signal, but as the gain control circuit 11R introduces a residual error, and because of the irregularity of the signal level luminance Y,

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  Convergent, final precision is achieved during the operation.

  following ration. Since the level of the luminance signal is slightly modified by the motion or vibrations of the portable television camera, the only correction described above is not sufficient to give a satisfactory result. In step 11, it is decided whether the MER content of the

  second address is within the predetermined, controlled range.

  If the MER content of the second address is outside the range or if there is an overshoot towards "00" or "FF" (F = 15), the indicator 20 gives an indication of error during of step 12. Then, the program advances to step 20 to set the BY color difference signal.

  by bypassing the adjustment steps of the difference signal

  R-Y color. This indicates that it is possible to adjust

  automatic white balance; in this case, after switching

  In manual mode, the optical system of the television camera is adjusted or corrected, for example by changing a filter;

  then, the operation described above is repeated again.

  If, on the other hand, the MFR content is in the expected range, ie in the case of an affirmative answer in the flowchart, the automatic adjustment is possible and the

program goes to step 13.

  In step 13, the computer 30 supplies the MRF content of the first address by the D / A converter 17 to the comparator 16 which compares it to the level of the difference signal.

of color R-Y.

  Then in step 14, the system decides on the comparison output. If the R-Y color difference signal has a high level, the program proceeds to step 15 in which the digit "1" is subtracted from the MER content at the second address. If the level of the R-Y color difference signal is lower, the program proceeds to step 16 in which the number "1" is added to the MER content at the second address. Then in step 17, the system decides the number N

  times during which the above operation was repeated.

  If the repetition of the operation corresponds for example to N = 15 or is less than this number, the program returns to step 10. If the number of repetitions N is set to 16 in step 17, the program advances to In this way, if the initial value is within the controlled range, the white balance adjustment is completed within the time period

  corresponding to this repetition of 16 times.

  In step 20, the switch 12 is set to the position in which the mixer 6B of the B-Y color difference signal is connected; the B-Y color difference signal is adjusted using the first and the third

  addresses, in the same way as described above.

  When setting the difference signal of

  B-Y color is complete, the program stops.

  Thus in this third montage, when the

  19 is closed during shooting, adjusting the balance

  free of white is done automatically. Then, when the RY and BY color difference signals are completely adjusted, the correction signals used to adjust the white balance of the RY and BY color difference signals are recorded as numerical values at the second and the third address in the computer 30. These digital values of the shooting of the original object, are

  read alternatively, for example for each sync signal

  and are sent to the sample circuits-

  swimming and holding 18R, 18B, which provides an image

  properly balanced white for the television camera.

  In this way, the adjustment of the balance

  According to the invention, the reference level of the video signal of the erasure period and the level of the video signal of the video scanning period are produced from the same signal line, which eliminates any risk of erasure. drift error or the like. In addition, as a rough correction is made using the difference between the levels, then a fine correction, it reduces the time required

setting.

  Whereas for the adjustment of the white balance according to the invention, a rough adjustment is carried out according to steps 1 to 10, then a fine adjustment, more precise during steps 11 to 20 (flow chart, FIG. limit itself if necessary to only steps 1 to 10 and delete the steps

11 to 20.

  Moreover, although in the embodiment

  above, the digital signal corresponding to the reference signal VRF is recorded in the random access memory RAM 33 in steps 4 and 5, the digital signal corresponding to the video signal VER is recorded in the random access memory RAM 33 in steps 6 and 7; the recorded contents are compared to step 8 but it is

  possible to reverse the order of the steps.

  In addition, the microcomputer used in this

  According to the invention, it is possible to perform all the complex adjustments simply by using the program, which simplifies the circuit for the implementation of the invention.

  Although the above description concerns the

  adjusting the balance of the color difference signals, this setting can also be applied to the difference signals

  of color G-R and G-B in the case of a camera with three tubes.

  Finally, you can do an automatic black balance using the same editing but simply change the program; it is also possible to make a fully automatic adjustment in three stages, automatic balancing

  of white -> automatic balancing of black -> self balancing

white matter.

Claims (2)

CLAIMS l1) A method of adjusting the white balance of a color television camera using a microcomputer having a read only memory (ROM), a random access memory (RAM), a central processing unit (CPU) and buses method, characterized in that a reference video signal (VF) is sampled in a reference interval (TB) of an input video signal (Vin) while the camera is analyzing a monochrome object , performing an analog / digital conversion of the sampled reference signal (VR) to give a reference signal in digital form, storing this digital reference signal in a first region of the memory (RAM) (33), sampling a color difference signal (RY) in a video scan interval (Tp) of the input video signal (Vin), an analog-to-digital conversion of the sampled color difference signal (RY) is performed to give a sig. In the case of a digital color difference, the digital color difference signal is stored in memory in a second region of the memory (RAM, 33), the content (MER) corresponding to the recorded digital color difference signal is calibrated or substituted. in the memory to coincide with the digital color difference (MER) signal recorded in the second region of the memory with the content (MRF) of the digital reference signal recorded in the first memory region and the level of the luminance signal (Y) to be mixed with the color difference signal (RY) as a function of the substituted memory content in the second memory region. An adjustment method according to claim 1, characterized in that a digital / analog conversion of the reference content (MRE) recorded in the first region of the memory is performed to obtain an analog reference signal, compared with the level of the analog reference signal and the input color difference signal (RY), the color difference content (MER) recorded in the second memory region is calibrated or substituted by bit scales, in according to the level of difference resulting from the comparison, the level of the luminance signal (Y) is adjusted as a function of the content (MER) of the color difference, substituted in the second memory t46141T) Adjustment method according to claim 2 , characterized in that the content of the color difference signal (MER) recorded in the second memory region is checked to see if this content is within the adjustable range of the system automatic white balance and the error is indicated by means of an indicator means according to the result of this control.   4) Adjustment method according to any one of   Claims 1 and 2, characterized in that the level is   of the luminance signal successively in two channels of color difference (R-Y, B-Y).    ) Color television camera giving a color television signal consisting of a luminance component and at least one color difference signal, with scanning intervals separated by erasing intervals, camera comprising a control circuit of the white balance for implementing the adjustment method   according to any one of claims 1 to 4, camera   in that it comprises a mixer (6R, 6B) for combining the color difference signal (RY, BY) and the color difference correction signal (aY), an adjustable gain control (11B) giving the color difference correction signal, this signal varying with the luminance component being proportional to the gain control signal which is   applied, a sampling circuit (13) of the difference signal   during one of the erase intervals (TB) to give a reference signal, and one of the scan intervals (Tp) to give a sampled color difference signal, a converter (17) to transform the signal   reference and the color difference signal, sample   digital storage means (33) having a plurality of memory positions for recording the converted reference signal (M- -) and the converted sampled color difference signal (MOR) at the different storage positions; means (16, 17, 30) for modifying the sampled, converted color difference signal so that the latter has substantially the same numerical value as the converted reference signal and means (18) for giving as   gain control signal, a level proportional to the   registered value corresponding to the difference signal of Izz   sampled, converted, modified.   ) Color television camera according to the   5, characterized in that it comprises a manually operated means for selectively starting the operation of adjusting the white balance. A television camera according to claim 5, characterized in that it comprises means for checking whether the sampled, converted, recorded color difference signal is outside a predetermined range and for giving an indication of this that the difference signal   of color sampled, converted, recorded, is outside laughing at this beach.   8) Color television camera according to the   5, characterized in that the means for providing a gain control signal comprises a digital converter /   analogue signal giving a level corresponding to the signal   color, sampled, converted, recorded, and sample and hold means for sampling the level during predetermined intervals and providing the signal   of gain control by means of adjustable gain control.