JP2004289276A - Television camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a television camera capable of sharply photographing a subject even when the subject is photographed through a glass pane or in a misty state. <P>SOLUTION: A maximum value detection section 5, an average arithmetic section 6 by each area, and a minimum value detection section 7 detect the video signal level of the darkest part of a subject and define the level to be a minimum level L. A correction value calculation section 9 compares the minimum level L with a reference value S to obtain a correction signal C. Then subtraction circuits 2, 3, and 4 subtract the correction signal C from video signals R1, G1, B1 so as to lower the video signal level to a proper level, thereby recovering the contrast of the subject. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a color television camera of a three-color separation system, and more particularly to a color television camera suitable when a wide dynamic range is required.
[0002]
[Prior art]
If a photograph is taken through a glass plate by a television camera or when photographing is performed in a fog state, the subject becomes hazy, information on the shape and color becomes ambiguous, and the entire screen becomes whitish.
[0003]
On the other hand, in a television camera, in order to obtain a wide dynamic range, a high-luminance portion of a video signal is often subjected to compression processing. In this case, if the entire screen becomes whitish under the above shooting conditions, Since the level of the video signal is shifted in the direction of high luminance, the gradation is reduced due to the compression processing, and as a result, the blurred object has low contrast and is difficult to see.
[0004]
In the case of a television camera, the color information of an output video signal is expressed as a level difference after converting three types of light separated by a prism or the like into an electric signal. Decreases, the color of the image becomes lighter, so that the contrast of the subject also decreases, and as a result, it becomes more difficult to see.
[0005]
By the way, in such a case, flare correction is applied in the related art (for example, see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-5-3569
[Problems to be solved by the invention]
The above prior art does not consider photographing through glass or in a state of fog, and has a problem in maintaining image quality under such imaging conditions.
[0008]
That is, the prior art corrects only flare to the last, and therefore, there is a problem in maintaining image quality under the above-described imaging conditions.
[0009]
An object of the present invention is to provide a television camera capable of clearly photographing a subject even when photographing through glass or in a state of fog.
[0010]
[Means for Solving the Problems]
The object is to compare the levels of the red, green, and blue components of a video signal for each frame period in a color television camera in which a high-luminance portion of the video signal is compressed to obtain an expanded dynamic range. Means for detecting the video signal of the color component having the maximum value, and capturing the video signal of the color component having the maximum value for each frame, dividing one frame screen into a plurality of areas, and Means for calculating the average value of the signal level, means for comparing the average value of the signal levels for each of the areas to detect the lowest value, and comparing the lowest value with a preset reference value, Means for detecting a level exceeding the minimum reference value as a correction signal, and subtracting the correction signal from each of a red component, a green component, and a blue component of the video signal, It is accomplished as performing compression processing of the luminance portion.
[0011]
At this time, the above object can be achieved even if the reference value is set by the minimum value when a specific subject is imaged.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a television camera according to the present invention will be described in detail with reference to the illustrated embodiments.
[0013]
FIG. 1 shows a first embodiment of the present invention. Here, a basic part of the television camera is a color image pickup head 1, which comprises a color separation optical system (prism) and an R (red) color. , G (green) color, and B (blue) image sensors.
[0014]
Then, the video signal R1 composed of a red component, the video signal G1 composed of a green component, and the video signal B1 composed of a blue component of the subject image output from the color imaging head 1 are first subtracted by respective color signal subtraction circuits. 2, 3, and 4 are input.
[0015]
Then, a correction signal C (described later) is subtracted by these subtraction circuits 2, 3, and 4, and becomes a red component video signal R2, a green component video signal G2, and a blue component video signal B2. It is supplied to a circuit or the like, where the high-luminance partial compression processing for expanding the dynamic range is performed.
[0016]
At this time, the video signals R2, G2, and B2 output from the respective subtraction circuits 2, 3, and 4 are input to the maximum value detection unit 5 for each frame. Here, first, among the video signals R2, G2, and B2, The one having the maximum level (peak value) during one frame period is selected as the video signal M for each frame, and is supplied to the average value calculation unit 6 for each area in the same frame unit.
[0017]
The area average calculation unit 6 sequentially receives the video signal M (any one of the video signals R2, G2, and B2) for one frame, and divides one frame screen into a plurality of, for example, n areas. The average value A (A1 to An) of the signal level in each area is calculated for each area and supplied to the lowest value detection unit 7 for each frame.
[0018]
The lowest value detection unit 7 compares the input average values A (A1 to An) for one frame with each other, detects the signal level of an area showing the lowest level among them, and determines this as the lowest level. The level L is supplied to one input of the correction value calculator 9. At this time, a predetermined reference value S preset from the reference level generator 8 is supplied to the other input of the correction value calculator 9.
[0019]
Then, the minimum level L supplied from the minimum value detection unit 7 is compared with the reference value S by the correction value calculation unit 9, and the correction signal C (= L) having a level where the minimum level L exceeds the reference value S is used. -S) is calculated for each frame, and this is input to the subtraction circuits 2, 3, and 4. As a result, video signals R2, G2, and B2 obtained by subtracting the correction signal C from the video signals R1, G1, and B1 are obtained. Will be done.
[0020]
Then, according to these video signals R2, G2, and B2, the subject does not become whitish and a clear image can be obtained even when photographing through glass or operating in a fog state. Hereinafter, the reason will be described.
[0021]
As described above, when shooting through a glass plate or shooting in a foggy condition with a television camera that widens the dynamic range by compressing the high-brightness part, the contrast of the subject appears to be reduced. The difficulty is caused by the fact that the whole screen becomes whitish and the level of the video signal shifts in the direction of high luminance, so that the gradation is suppressed by the compression processing.
[0022]
Therefore, in order to suppress a decrease in contrast due to such a reason, it is only necessary to suppress a shift of a video signal level in a high luminance direction, which is caused by the entire screen becoming whitish.
[0023]
Here, in the above embodiment, regarding the lowest level L output from the lowest value detecting unit 7, it can be considered that this corresponds to the video signal level of the darkest part of the subject.
[0024]
Therefore, subtracting the lowest level L from the video signals R1, G1, and B1 removes the shift of the video signal level in the high-luminance direction, so that the reduction in contrast should be suppressed. The video signal level in the darkest part is at a certain level even if the entire screen is not whitish.
[0025]
Therefore, in the above embodiment, instead of subtracting the lowest level L from the video signals R1, G1, and B1 as it is, a reference value S is set to the lowest level L, and correction of a level at which the lowest level L exceeds the reference value S is performed. The signal C is subtracted.
[0026]
Therefore, according to this embodiment, when the entire screen becomes whitish, the video signal level can be reduced to an appropriate level in accordance with the degree thereof, and it is possible to prevent the subject from being difficult to see due to a decrease in contrast. it can.
[0027]
Next, another embodiment of the present invention will be described. First, FIG. 2 shows a second embodiment of the present invention, in which a time constant circuit 10 includes a correction signal output from a correction value calculating unit 9. The function of this embodiment is to reduce the change in C and to supply the corrected correction signal T to the subtraction circuits 2, 3, and 4. The other components are the same as those in the first embodiment shown in FIG.
[0028]
Here, although not particularly described in the embodiment of FIG. 1 described above, the correction signal C output from the correction value calculation unit 9 is updated one after another in frame period units. The correction signal C changes largely in a step-like manner, and the state of the image may change abruptly as it is.
[0029]
Here, according to the embodiment shown in FIG. 2, the time constant circuit 10 is provided and the change of the correction signal C is mitigated. It is possible to eliminate the possibility of the change.
[0030]
By the way, the embodiments described with reference to FIGS. 1 and 2 each take in the video signals R2, G2, and B2 output from the subtraction circuits 2, 3, and 4, generate the correction signal C, and generate the correction signal C. Although the present invention is implemented by the feedback control method in which the input is returned to the inputs 3 and 4, the present invention may be implemented by the feedforward control method.
[0031]
Here, FIG. 3 shows a third embodiment of the present invention, which corresponds to the embodiment of FIG. 1 implemented by a feedforward control method, and FIG. 4 shows a fourth embodiment of the present invention. In form, this corresponds to an implementation of the embodiment of FIG. 2 in a feed-forward control manner.
[0032]
Accordingly, these embodiments of FIGS. 3 and 4 have the same components as those of the embodiments of FIGS. 1 and 2, respectively, and the video signal output from the color imaging head 1 before the subtraction circuits 2, 3, and 4. The only difference is that a correction signal C is generated by taking in R1, G1, B1 and input to the inputs of the subtraction circuits 2, 3, 4 together with the video signals R1, G1, B1. .
[0033]
Therefore, according to the embodiment of FIGS. 3 and 4, it is apparent that the same operation as the embodiment of FIGS. 1 and 2 can be obtained, and as a result, the same operation and effect can be obtained. Detailed explanation is omitted.
[0034]
By the way, as is easily understood from the above description, in the embodiment of the present invention, how to set the reference value S output from the reference level generator 8 is an important requirement.
[0035]
Here, the setting of the reference value S may be adjusted so as to obtain an appropriate image while actually photographing with a television camera. In this case, however, the setting requires some skill.
[0036]
Here, FIG. 5 shows a fifth embodiment of the present invention, in which the output of the minimum value detection unit 7 is sampled at a predetermined timing and set as the reference value S of the reference level generation unit 8. The other configuration is the same as that of the embodiment of FIG.
[0037]
The predetermined timing at this time is, for example, when a test pattern is taken as a subject and shooting is performed under standard imaging conditions, and the output of the lowest value detection unit 7 at this time is taken as a reference value S and set. By doing so, settings suitable for the imaging environment can be easily obtained.
[0038]
Here, FIG. 5 describes the case where the present invention is applied to FIG. 1, but it is needless to say that the present invention can be similarly applied to other embodiments, that is, the embodiments of FIGS. 2 and 3 and FIG. .
[0039]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, a subject can be image | photographed clearly even if it image | photographs through glass or the state which was fog.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of a television camera according to the present invention.
FIG. 2 is a block diagram showing a second embodiment of the television camera according to the present invention.
FIG. 3 is a block diagram showing a third embodiment of the television camera according to the present invention.
FIG. 4 is a block diagram showing a fourth embodiment of the television camera according to the present invention.
FIG. 5 is a block diagram showing a fifth embodiment of the television camera according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Color imaging heads 2, 3, 4 Subtraction circuit 5 Maximum value detection unit 6 Average value calculation unit for each area 7 Minimum value detection unit 8 Reference level generation unit 9 Correction value calculation unit 10 Time constant circuit

Claims (2)

In a color television camera in which a high-luminance portion of a video signal is compressed to obtain an expanded dynamic range,
Means for comparing the levels of the red component, the green component, and the blue component of the video signal for each frame period to detect a video signal of a color component having a maximum value,
Means for capturing the video signal of the color component having the maximum value for each frame, dividing one frame screen into a plurality of areas, and calculating an average signal level for each area;
Means for comparing the average value of the signal levels for each area to detect the lowest value,
A means for comparing the lowest value with a preset reference value, and detecting a level exceeding the reference value of the lowest value as a correction signal,
A television camera, wherein the correction signal is subtracted from each of a red component, a green component, and a blue component of the video signal, and then the high-luminance portion is compressed. The television camera according to claim 1,
A television camera, wherein the reference value is set by the lowest value when a specific subject is imaged.

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