JPS61131696A - White balance device - Google Patents

Abstract

PURPOSE:To eliminate the error of white balance caused by the object by controlling with a partial compression against the color temperature variation in case each chrominance signal gain is controlled by the output from the color temperature sensor. CONSTITUTION:The signals obtained by the color temperature sensors 1R, 1G, and 1B are operated by a subtracting circuit 2 and a logarithmic- compressing circuit 3, converted to digital signals by an A/D converter 4, and are supplied to a system controller 5. After the controller 5 performed the operation to generate the control voltage for gain control amplifiers 11R and 11B at each color temperature, the signals are converted by a D/A converter 6, and are supplied to the control terminals of the amplifiers 11R and 11B via clipping circuits 15 and 16. Therein, among the signals obtained from a pick-up device 7, the gains of the R-signal and the B-signal are controlled to furnish a proper white balance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a white balance device for a video camera, and particularly to an automatic tracking type white balance device that constantly feeds back information from a color temperature sensor to a signal system.

[Prior art]

Conventionally, this type of automatic tracking white balance device uses the color temperature information of the light source obtained from the color temperature sensor and the color temperature correction curve shown in Figure 1 to calculate the gain control amplifier of the color signal system. I decided on the control voltage and took care of the white balance.

In other words, in the conventional method, the ratio of color temperature to color signal R/B
, R/G, and B/G are from the radiation side of the blank, color temperature 5500'K''t'R: G: B=1: 1
: When normalized to 1, the result is as shown in FIG. 2. Using the normalized RSGSBFti, minutes, the correction gains G, Gm at a certain color temperature K can be expressed as follows. On the other hand, the relationship between the control voltages vl and vjuku of the gain control amplifier and the gains GK and Gl is as follows:
From Figure 2, it becomes. From equations (11, (21, (31, (4)), Vt
, Vs is expressed as. The actual calculation is, for example, R
Regarding the ch system, it is performed as follows. In other words, the color temperature information obtained by the temperature sensor is converted to -4- type by a divider/logarithm amplifier, and then A/D converted.
After the calculation of equation (5) is performed by the system controller, it is D/A converted and becomes the Huntroll voltage V wing.

However, the drawback of this type of automatic tracking white balance method is that if a highly saturated subject occupies a relatively large area in the direction that the color temperature sensor is facing, the output from the sensor will be independent of the color temperature. This caused the white balance to malfunction during development. For example, if a red subject occupies a large area in front of the camera, the output of the color temperature sensor will increase even though the color temperature of the light source is constant, and as a result, vl in equation (5) will become smaller and the signal system will change. I had an inconvenience where I lowered the gain and the screen turned bluish.

〔the purpose〕

An object of the present invention is to eliminate such a phenomenon, that is, to provide a white balance device that can eliminate errors in white balance caused by a subject.

〔Example〕

FIG. 3 shows an embodiment of this invention, 1R91G.

Reference numeral 1B denotes a color temperature sensor, and the shaded portions are filters each adapted to the R, G, and B characteristics of the color filter of the imaging device 7. 2 and 3 are division 1 logarithmic compression circuits, 4 is an A/D converter, 5 is a system controller, 6 is a D/A converter, and T is an imaging device (
With color filter) 8 is S/H% 9R, 9G, 9B
is s/H, 10R, 1 for separating R, G, and B signals.
0G, 10B, IOY are LP for R, G, B, Y signals
F.

11R, 11B are gain control amplifiers, 12R,
12G, 12B, 12Y Fir conversion circuits; 13 is a matrix circuit; 14 is an NTSC coater; and 15 and 16 are IJ emitter circuits for performing compression according to the present invention.

With this configuration, the color temperature sensor IR
, IG, and 1B are calculated in the form of G, , G, B, O, respectively, in the division/logarithm compression circuit 2.3, converted into a digital signal by the A/D converter 4, and sent to the system controller 5. Then, with this Sysfun 5, gain control amplifiers 11R and 11 at each color temperature are used.
After the calculation for generating the control voltage of B is performed,
A D/A converter 6 performs D/person conversion, and a clip circuit 15.
Gain control amplifier 1 with upper and lower limits at 16
Leads to control terminals 1R and 11B.

On the other hand, the image signal obtained by the imaging device 7 is
A portion goes to LPFiQY for the luminance signal system, and the rest goes to S/H9R for separating color signals.

It reaches 9G and 9B, and becomes R, G, and B signals through LprloR, 10G, and 10B. Of these, for the R and B signals, the white balance gain control amplifier IIR, 11Bt-path, and the G signal are left as they are, respectively.
After passing through circuits 12R, 12G, and 12B, the luminance signal is also γ-converted by an r-conversion circuit 12Y, and then reaches a matrix@path 13. Here, after being coded into color difference signals R-Y and B-Y, the NTSC encoder 14 outputs the signals as NTSC signals.

In short, the limit circuits 15 and 16 are provided to limit or compress the mount roll voltage as shown by the dotted line in FIG. It is possible to prevent color shift 7 when the color temperature information deviates greatly due to a highly saturated subject. Note that as a compression method, a logarithmic compression circuit or the like may be used instead of the limit circuits 15 and 16.

The present invention is effective in systems such as still video cameras that obtain one-shot still image information using a trigger switch. Furthermore, in a movie camera that obtains continuous images, in addition to the above method, the limiter circuits 15 and 16 are integrated circuits with large time constants,
Even if a highly saturated object appears for a very short time, it is possible to prevent color shift by compressing its influence per unit time.

In the above embodiment, the gain control amplifier 11R, 1
Excessive changes in gain were suppressed by analog-limiting the control voltage of 1B, but this effect is not the same even if the system controller 5 calculates a compressed control voltage as shown by the solid line in Figure 4. be. Also, if you use Syscon 5 to create a compressed control voltage as shown in the solid line compared to the original control voltage (dotted line) as shown in Figure 5, it will be possible to create a control voltage that is compressed as shown in the solid line in Figure 5. In this case, a slightly reddish image can be obtained, and in areas with a high color temperature (bluish), a slightly bluish image can be obtained, making it possible to perform coloring operations that are more in tune with the human eye.

〔effect〕

As explained above, (1) according to the present invention, it is possible to eliminate errors in white balance due to the subject.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the color temperature normalized to 5500° and the color sum pair value, Figure 2 is Gay)
FIG. 3 is a block diagram showing an embodiment of the present invention, and FIGS. 4 and 5 are graphs showing the control voltage of the gain control amplifier. IR, IG, 1B・・・・・・Color temperature sensor 1
1R, 11B......Gain control amplifier 15.16......Limiter circuit

Claims (1)

[Claims] A white balance device comprising a control means for controlling the gain of each color signal according to an output from a color temperature sensor, and performing the control by at least partially compressing changes in color temperature.