JPH04107082A - Negative picture signal processing circuit - Google Patents

Abstract

PURPOSE:To realize the optimal white balance of the color signals of negative pictures by adjusting the color signals so that the maximum levels of the three kinds of the color signals can be coincident with each other, and the minimum levels of the three kinds of the color signals can be coincident with each other. CONSTITUTION:Three primary color signals G, R, and B indicating picked-up object images are outputted from an image pickup device 10. A peak detection circuit 12 detects both the maximum level and the minimum level of input signals, and the maximum level and the minimum level correspond to a black peak level and a white peak level, respectively. A microcomputer 11 controls variable gain amplifying circuits 15 and 16 by using input data indicating the black and white peak levels in order to adjust the white balance. Moreover, the black and white peak levels, and tonal characteristics of the color signals G, R, and B are made coincident with each other by gamma correcting circuits 41, 43, and 45.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention The white peak level and black peak level of three types of color signals R, G, and B obtained by capturing a negative image are detected, respectively. Then, the amplitude and level are adjusted so that the white peak levels of the second rapid signals R, G, and B match, and the black peak levels of the brown signals R, G, and B match.

In addition, the signals representing the levels of these detected white peaks and black peaks are superimposed on the first half and the second half of the blanking period of each color signal R, G, and B, so that they can be used in the subsequent signal processing. .

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative image signal processing circuit, and more particularly to a processing circuit for white balance adjustment.

In this specification, negative means negative.
ve), and negative image refers to a negative image or negative picture. Also, positive means positive.
tive), and positive image refers to a positive image or positive image.

Prior Art and its Problems To capture a negative image, for example, an image displayed on a negative film is photographed and the image remains as a negative.

Alternatively, it is necessary in a system where the image is inverted to positive and displayed on a large display screen or projected onto a screen. This system is a new system that replaced the optical so-called overhead projector.
Used at research presentations, etc. A video signal obtained by capturing a negative image has different characteristics from a video signal obtained by capturing a positive image, and therefore cannot be treated in the same way.

Figure 3 shows an example of the gradation characteristics (logarithmic expression) of a negative film, which shows the relationship between the amount of incident light when the negative film is exposed and the resulting developed density of the negative film after development. It shows. Areas that are not exposed at all (
Completely light-shielded area) A has the lowest density, and completely exposed area B has the highest density. The brightness range of the photographed image is not the range from parts A to B mentioned above, but the range from the darkest part to the brightest part of the photographed image, as shown as the usage range C. Therefore, the darkest part of the photographed image must be the black level of the video signal, and the brightest part must be the white level of the video signal. Therefore, it is necessary to detect the upper and lower limits of the usage range C.

When the negative image is a color image, the color gradation characteristics of the three primary colors R, G, and B that make up the color are different from each other as shown in Figure 4, and each color gradation characteristic has a usage range (
There is a problem that the values (represented by thick lines) are different from each other. If the color gradation characteristics differ depending on the color, the intermediate tones of the reproduced image will be discolored, and if the usage range differs, there will be a problem that color balance cannot be achieved. The above problem similarly occurs with complementary colors of yellow, magenta, and cyan.

′! Figure s5 shows a conventional negative image signal processing circuit. Camera (video camera, still video camera)
Of the three primary color signals G, R, and B output from the imaging device 60 such as
5. H, and white balance adjustment is performed by a known method. When a negative image is captured, this white balance adjustment adjusts the peak level of the negative image signal (
This is called the black peak level), that is, the black peak ψ level when inverted to positive is adjusted so that the three primary color signals G, R, and B match.

The color signals G, R and B after white balance adjustment are as follows.

On the one hand, it is applied to gamma correction circuits 61.83 and 65, respectively, and on the other hand, it is inverted by inversion circuits 71.73 and 75, respectively (the negative image signal is inverted to a positive image signal), and the blanking mix circuit 72.7
4 and 76, the blanking signal BLK is superimposed on the blanking period, and the gamma correction circuit 62
．． 64 and 6B, respectively. The same gamma correction curve is set for the positive gamma correction circuits 61, 63 and 65. Negative gamma correction circuit 82.6
4 and 86, gamma correction curves are set according to the gradation characteristics of G, R, and B, and the gradation characteristics after gamma correction are G.
The three primary colors of , R and B are matched.

The changeover switches 51, 52 and 53 are for each color signal G, R.
and B for switching between a positive gamma-corrected color signal and a negative gamma-corrected color signal. These switches 51, 52 and 5
The output color signals G, R and B of No. 3 are given to a matrix circuit 83, which outputs a luminance signal Y and color difference signals R-Y, B-Y.
is converted to Furthermore, these signals Y, RY and B
-Y is converted into an NTSC format video signal by the encoder 84 and output.

In such a conventional circuit, gamma correction curves corresponding to the gradation characteristics of each color are set in the negative gamma correction circuits 62, 84 and 6B, and the gradation characteristics of each color signal after gamma correction are uniform. The above-mentioned problem of coloring in intermediate tones does not occur.

However, in white balance adjustment, color signals G and R
Since the gains of the variable gain amplifier circuits 85 and 86 are only adjusted so that only the black peak levels of and B match, when this is inverted to positive, the black peak levels on the positive match. However, there is a problem that the white peak level on the positive does not match and the white balance is not appropriate.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION An object of the present invention is to provide a processing circuit that can realize an appropriate white balance of color signals of a negative image.

Structure 2 of the Invention Functions and Effects The negative image signal processing circuit according to the present invention detects the maximum level (black peak level) and minimum level (white peak level) of each of three types of color signals obtained by capturing a negative image.
A peak detection circuit detects the three types of color signals such that the detected maximum levels are mutually equal for the three types of color signals and the detected minimum levels are mutually equal for the three types of color signals. It is characterized by comprising a circuit for adjusting the amplitude and the maximum or minimum level.

According to this invention, the color signals are adjusted so that the maximum levels of the three types of color signals match each other and the minimum levels of the three types of color signals match each other. Therefore, the black peak levels of the three types of color signals match each other, and the white peak levels of the three types of color signals also match each other. In this way, white.

Since the black peak levels are the same for the three types of color signals, appropriate white balance adjustment is always achieved even if the first sudden signal remains negative or is inverted to positive.

The adjustment circuit includes, for example, a variable gain amplifier circuit that adjusts the amplitudes of at least two types of color signals so that the differences between the detected maximum level and minimum level are equal to each other for the three types of color signals, and a variable gain amplifier circuit that adjusts the amplitude of at least two types of color signals, and a maximum level or and a level adjustment circuit that adjusts the levels of three types of color signals so that their minimum levels are equal to each other.

Preferably, a gamma correction circuit is provided to equalize the gradation characteristics of the three types of color signals, and the gamma correction circuit is provided with the level adjustment circuit.

More preferably, a clamp circuit for aligning the levels of the DC components of the three types of color signals to a constant level is provided before the peak detection circuit for each of the three types of color signals. This makes it possible to reliably detect the maximum level and minimum level without being affected by DC signal components.

The negative image signal processing circuit according to the present invention detects the detected maximum It further includes a blanking mix circuit that superimposes signal components representing the level and minimum level, respectively.

Since the signal component representing the black peak level and the signal component representing the white peak level are added at different positions on the time axis during the blanking period when there is no signal component representing the image, the signal component representing one image is However, since the black and white peak levels are preserved in the color signal, they can be used by the subsequent signal processing circuit.

Description of examples FIG. 1 shows an embodiment of the invention.

An imaging device 10 such as a still video camera or a video camera sends three primary color signals G and R representing a captured subject image.
and B are output. If the subject image is a stationary object such as a negative film, the color signal representing the image of the negative film has a fixed period (for example, 1760 seconds).
will be output repeatedly. Color signals G, R and B output from the imaging device 10 are shown in FIG. 2a. In this way, the color signals G, R, and B reflect the above-mentioned differences in gradation characteristics for each color, and the levels of the DC signal components generally also differ.

Among these color signals, the color signal G is directly connected to the clamp circuit 2.
1, and the other color signals R and B are given an appropriate gain (1
(in some cases, the signal may be less than or equal to 100%) and then provided to clamp circuits 22 and 23, respectively. Clamp circuit 2
The same clamp level is set for 1.22 and 23, and these clamp circuits 21.22 and 23
As a result, the DC signal components of the color signals G, R, and B are uniform.

The color signals G, R and B outputted from the clamp circuits 21, 22 and 23 are applied to blanking mix circuits 31, 32 and 33, respectively, on the one hand, and to a changeover switch (multiplexer) 24 on the other hand. The changeover switch 24 is the microcomputer 1
1, and one color signal G, R, and B are sequentially applied to the peak detection circuit 12.

The peak detection circuit 12 detects the maximum level and minimum level of the input signal. Color signal G.

When R and B represent a negative image such as a negative film, the maximum level corresponds to the black peak level and the minimum level corresponds to the white peak level.
Use level terminology. When the color signal G is input to the peak detection circuit 12 by the changeover switch 24, the black and white peak levels of the color signal G are respectively detected.

The time during which the changeover switch 24 selects the color signal G may be the period during which an appropriate area within one screen is being scanned. This is equivalent to setting a window on the screen and detecting the black and white peaks within the window. The same applies to the other color signals R and B.

The black and white peak levels of the two color signals G, R and B detected in this manner are provided to the microcomputer 11. The microcomputer 11 uses the input data representing the black and white peak levels to calculate the difference between the black peak level and white peak level of the private signal G.

The difference between the black peak level and the white peak level of the color signal R and the difference between the black peak level and the white peak level of the one color signal B (these are shown as D in FIG. 2b) are equal to each other. The gains of the variable gain amplifier circuits 15 and 18 are controlled so that the white balance is adjusted. The color signals G, R and B after white balance adjustment and DC component clamping are shown in FIG. 2b. Black peak level and white peak level of three color signals G, R and B
Levels are not yet matched. Furthermore, the difference in gradation characteristics of the single color signals G, R, and B has not yet been adjusted.

The white balance-adjusted color signals G, R, and B are sent to the blanking mix circuits 31, 32, and 3 as described above.
3 are given respectively. These blanking mix circuits 31. Two types of blanking timing signals BLKI and BLK2 are input to H and 33. The blanking timing signal BLKI is a signal that becomes H level during the first half of the blanking period, and the blanking timing signal BLK2 is a signal that becomes H level during the second half of the blanking period. Blanking/
The mix circuit 31 receives the detected black peak of the color signal G.
Signals representing the level and white peak level are provided from the microcomputer 11. Similarly, the blanking mix circuit 32 receives signals representing the detected black peak level and white peak level of the color signal R, and the blanking mix circuit 33 receives signals representing the detected black peak level and white peak level of the color signal B. Signals representing the level and white peak level are provided from the microcomputer 11, respectively. Blanking φ mix circuit 31.3
2 and 33 are blanking timing signals BLK
While I is at H level.

Pulse signals representing the corresponding white peak levels are superimposed on the color signals G, R, and B, and while the blanking timing signal BLK2 is at H level, the pulse signals representing the corresponding black peak levels are superimposed on the color signals G, R, and B. Superimpose on R and B.

In this way, the color signals G, R and B, to which pulse signals representing the white peak level and the black peak level are added during the blanking period, are applied to the blanking timing signal BLK1. It is shown in FIG. 2C together with BLK2. Since the white peak level and black peak level are saved during the blanking period of the color signals G, R, and B, these white and black peak levels can be used in the subsequent circuit. For example, the black peak level is inverted to positive and then used as the black reference level of the video signal. Further, the white peak level is used for clamp processing in gamma correction, which will be described later.

The output signals of the blanking mix circuits 31, 32 and 33 are applied on the one hand to negative gamma correction circuits 41, 43 and 45, respectively, and on the other hand to positive gamma correction circuits 42, 44 and 46, respectively.

G for negative gamma correction circuits 41, 43 and 45;
Gamma correction curves are set according to R and B gradation characteristics. These gamma correction circuits 41, 43 and 4
In step 5, each input signal (color signals G, R, and B) is clamped so that their white peak levels are at a predetermined level and match, and the gradation characteristics after gamma correction are adjusted to G according to the gamma correction curve. , R and B are each gamma corrected so that they match. The output color signals G, R and B of the gamma correction circuits 41, 43 and 45 are shown in FIG. 2d. As can be seen from this figure, the color signals G, R, and B have the same black peak level, the same white peak level, and the same gradation characteristics.

The output signals of gamma correction circuits 41, 43 and 45 are then inverted to positive by inverting circuits 57, 58 and 59, respectively. The signal after this inversion is shown in Figure 2e.

The same gamma correction curve is set for the positive gamma correction circuits 42, 44 and 46. of course.

Different gamma correction curves may be set for these correction circuits 42, 44 and 4B as well.

The outputs of the gamma correction circuits 41 and 42 are sent to the changeover switch 51, and the outputs of the gamma correction circuits 43 and 44 are sent to the changeover switch 52.
The outputs of the gamma correction circuits 45 and 4B are connected to the selector switch 5.
3, respectively.

The changeover switches 51, 52 and 53 are for each color signal G,
It is provided for each of R and B and switches between a two-positive gamma-corrected color signal and a negative gamma-corrected color signal. Of course, these selector switches 5
1.52 and 53 are preferably interlocked. The output color signals G, R and B of these switches 51, 52 and 53 are applied to the matrix circuit 13 and converted into a luminance signal Y and color difference signals RY, BY. Furthermore, these signals Y, RY, and B-Y are converted into NTSC format video signals by an encoder 14 and output.

The encoder 14 has a blanking timing signal BL.
K3 is given. As shown in FIG. 2f, this timing signal BLK3 is a signal representing a blanking period (at L level during this period), and the timing signal BLK3
This is a pulse-like signal with a width slightly wider than the combined width of I and BLK2 pulse widths. During the L level period of timing signal BLK3, signals Y, R-Y and B-Y
is blanked to match each signal level (i.e., black level) during the H level period of the timing signal BLK2, so that the signal component representing the blanking period of the NTSC format becomes the signal Y.

Assigned to RY and BY. The final N
The TSC output is shown in Figure 2g.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention. 2a to 2g are waveform diagrams showing output signals of each block of the circuit shown in FIG. 1. FIG. FIG. 3 is a graph showing the gradation characteristics of an image expressed on a negative film, and FIG. 4 is a graph showing how the gradation characteristics differ depending on the color. FIG. 5 is a block diagram showing a conventional example. IO...imaging device. 11...Microcomputer. 12...Peak detection circuit. 15, 18...Variable gain amplifier circuit. 21, 22.23... Clamp circuit. 31, 32.33...Blanking mix circuit. 4142, 43.44.45.4B... Gamma correction circuit. Agent for the above patents: Fuji Photo Film Co., Ltd.
Person Patent Attorney Ken Ushiku Figure 3 Figure 4 Figure 1

Claims (5)

[Claims] (1) A peak detection circuit that detects the maximum level and minimum level of each of the three types of color signals obtained by capturing a negative image, and a peak detection circuit that detects that the detected maximum levels are mutually equal and detected for the three types of color signals. A circuit that adjusts the amplitude and maximum or minimum level of three types of color signals so that the three types of color signals have the same minimum level. A negative image signal processing circuit equipped with (2) a variable gain amplification circuit for adjusting the amplitudes of at least two types of color signals such that the difference between the detected maximum level and minimum level is mutually equal for the three types of color signals; 2. The negative image signal processing circuit according to claim 1, further comprising a level adjustment circuit that adjusts the levels of the three types of color signals so that their levels or minimum levels are equal to each other. (3) Processing of a negative image signal according to claim (1), further comprising a gamma correction circuit for aligning gradation characteristics of the three types of color signals, and the gamma correction circuit includes the level adjustment circuit. circuit. (4) Signal components representing the maximum level and minimum level detected in the first and second half of the blanking period of three types of color signals adjusted so that the difference between the maximum level and the minimum level is mutually equal The negative image signal processing circuit according to claim 2, further comprising: a blanking mix circuit that superimposes each of the following. (5) Claim (5) wherein a clamp circuit for aligning the levels of the DC components of the three types of color signals to a constant level is provided before the peak detection circuit for each of the three types of color signals.
1) The negative image signal processing circuit according to item 1).