JP2884384B2 - Video signal compression method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal compression method for compressing an output video signal output from an image pickup device such as an image pickup tube and a solid-state image pickup device used in, for example, a television camera. The present invention relates to a technique for preventing the occurrence of false contour enhancement accompanying a change.

[0002]

2. Description of the Related Art In a television camera using an image pickup device such as an image pickup tube and a solid-state image pickup device, the dynamic range of the device itself is as large as about 400 to 600%. Compress the signal for use. A knee circuit is provided with a certain level (knee point) because an output level of a video signal becomes too large when an excessive amount of light enters an image pickup device such as an image pickup tube and a solid-state image pickup device. Circuit. When this is performed by an analog circuit, a circuit as shown in FIG. 5 is obtained. When the input signal gradually rises from the left to the right of the screen as shown by the line a in FIG. 6, the output signal becomes the knee point level due to the characteristics of the diode in the circuit as shown by the line b in FIG. Compressed smoothly around. However, the bending characteristics near the knee point level are uniquely determined by the characteristics of the diode used.

When the knee circuit is formed by a digital circuit, the compression is not performed smoothly because there is no effect of the diode characteristic as in the analog circuit. In order to compress a video signal by a digital circuit, an output level larger than a knee point is simply linearly compressed. That is, compression is performed at the knee point so as to have a polygonal line characteristic. Such a conventional video signal compression device will be described with reference to FIG. When the input video signal y is input from the input terminal 1, the input level y of the video signal is compared with the knee point level KP by the comparator 2. When the input level y is smaller than the knee point level KP, the input level y becomes The video signal is not compressed and output from the output terminal 12 via the switch 11 as it is.

When the input level y is equal to or higher than the knee point level KP, the level difference (y-KP) is detected by the level difference detector 5, and the level difference (y-KP) is detected.
P) is multiplied by a predetermined compression coefficient k satisfying 0 ≦ k <1, and the multiplication result is added to the knee point KP. Then, the video signal is output from the output terminal 12 via the switch 11 with the added value as the output level Y. That is, the data is compressed and output with the broken line characteristic as shown in FIG.

[0005]

However, in the compression characteristic having a broken line at the knee point KP, a harmonic component appears at a broken portion of the broken line, that is, a knee point portion. When the image is displayed on a monitor television, the image is switched stepwise from non-compression to compression, so that the image is emphasized by the outline emphasizing circuit by erroneously judging the part as an outline, and is not a true outline but a false outline, which is not appropriate. .

Further, in the case of an analog circuit as shown in FIG. 5, even if an attempt is made to obtain a characteristic in which the output level of a video signal changes smoothly with respect to a change in input level, the characteristic at the bent portion will not be equal to that of the diode used. Uniquely determined by characteristics and cannot be changed freely. By the way, there is a method of using a look-up table as a method for avoiding the polygonal line characteristic as shown in FIG. This is a method in which the input / output characteristics are stored in advance in a look-up table formed of a ROM or the like so that the output signal becomes like the line b in FIG. 6 with respect to the level of the input signal.

However, this method has the following problems. When the quantization level is 128, which is 30% of the video signal level, the quantization level of the dynamic 600% input signal is 2560, and the RAM and ROM used for the look-up table require 2560 words. Further, depending on the variable range of the compression coefficient K, a capacity for the variable range is required. For example, assuming that the range of K is from 0 to 1, 11 steps (for example, 0.0,
0.1, 0.2,. . . , 0.9, 1.0), the capacity of the ROM is at least 256 × 11 = 282
60 words are required.

When a look-up table is used to obtain an output signal compressed for all dynamic levels of an input signal, the capacity of the look-up table becomes considerably large. Would. The present invention has been made in view of such a conventional problem.
It is an object of the present invention to provide a video signal compression method in which the output level of a video signal smoothly changes with respect to a change in an input level and in which a false contour signal is prevented from being generated.

It is another object of the present invention to provide a video signal compression method capable of freely setting a characteristic in which an output level of a video signal changes smoothly with a change in an input level.
In addition, the present invention provides a video image that can be minimized by using a look-up table only within a predetermined range of the input signal level even when compression is performed using the look-up table. It is an object to provide a signal compression method.

[0010]

According to the present invention, there is provided an image processing apparatus comprising:
When the input level of the signal is higher than a predetermined value, the input level
Compression coefficient k (0 ≦ k <1.0) to the difference between
Increase in the difference between the multiplied value and the input level and the predetermined value
Multiplied by (1.0-k) to a value that smoothly increases monotonically according to
The value obtained by adding the calculated value and the predetermined value is output as a video signal.
Force level .

Further, the input level of the video signal is
Output at a level equal to the input level when it is less than the specified value.
Configuration.

Further , a difference between the input level and the predetermined value is provided.
The value that smoothly and monotonically increases with the increase of
The rate of increase was gradually reduced to 0 for large values.

[0013]

According to the above arrangement, the input level is equal to or higher than the predetermined value.
, The level difference between the input level and the predetermined value
A value obtained by adding a value obtained by multiplying the compression coefficient k to the predetermined value is:
This is the value obtained by the conventional compression method.
A value that smoothly and monotonically increases as the difference increases (1.0-
k) Just perform a simple process of adding the value multiplied by
It is possible to easily increase the compression ratio smoothly.
You. Here, it is divided into two values and added to a predetermined value.
When trying to set the compression level to a desired value,
It is sufficient to change the value of the compression coefficient k, and change the compression coefficient k.
Even so, the increase rate at both ends of the predetermined range does not change,
A smooth connection can be maintained.

[0014]

[0015]

When the input level of the video signal is less than a predetermined value , if the video signal is output at a level equal to the input level, the video signal is output without the input level being compressed.
You. Furthermore, as the difference between the input level and the predetermined value increases, the slippage increases.
The value that increases monotonically seems to increase at a rate
Is gradually reduced to 0, the rate of increase becomes 0
Above the power level, the output level increases with the input level.
Then, it increases smoothly and continuously.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing an embodiment of the present invention. When the input level exceeds a predetermined value level, the circuit shown in FIG. Is a circuit for compressing so as to have a characteristic that smoothly changes in response to a change in the predetermined point.
And the end level within the predetermined range is defined as the knee curve end point KE.

FIG. 2 shows a conceptual diagram of the above. In FIG. 1, the comparator 2 compares the input level y of the video signal input to the input terminal 1 with the knee point level KP, and the comparator 6 compares the input level y of the input video signal with the knee curve. A magnitude comparison with the endpoint KE is performed. The level difference detector 5 detects a level difference (y-KP) between the input level y and the knee point KP.

The multiplier 8 sets the compression coefficient to k (0 ≦ k <1).
As the level difference (y−y) detected by the level difference detector 5.
KP) is multiplied by k. The ROM (read only memory) 7 is a memory used as a look-up table, and outputs 0 when the level difference (y-KP) is 0, as shown in FIG. When the level difference (y-KP) is (KE-KP), the maximum value is output, and as the increasing tendency, the rate of increase gradually decreases from 1 as the level difference (y-KP) increases, and the level increases. Data having differential characteristics such that the rate of increase becomes zero near the difference (y-KP) near (KE-KP) is stored in advance. Note that the level difference (y-KP) is (KE-K
The maximum value output at the time of P) is called the maximum value CL of the look-up table.

The look-up table stored in the ROM 7 is created as follows. Knee processing is
Since the output level is suppressed to 110% or less when the input level is high, when the most compressed output is obtained, that is, when the compression coefficient k is 0, for example, the output signal is set to 1
It should be suppressed to 02% or less. If the input level is 9
It is assumed that an output having a characteristic that is smoothly compressed is obtained at a level in the range of 5% to 125%. In this case, the knee point KP is 95% and the knee curve end point KE is 125
%. Also, the maximum value C of the lookup table
L should be set to 102% −95% = 7%, but is set to 6.56% for convenience of conversion to the quantization level.

Hereafter, the quantization level is set to 128 in units of 30% of the video level. The range from the knee point KP to the knee curve end point KE is 30% (= 125−
95), which is 128 when converted to a quantization level, so that the capacity of the look-up table is 128 words.
Also, since the maximum value CL of the look-up table is 6.56% at the video level, it is 28 × at the quantization level.
(6.56 × 128/30).

Therefore, as shown in Table 1, the data stored in the look-up table starts from 0 and ends at the maximum value 28, and the rate of increase is initially 1 and gradually becomes 0.

[0023]

[Table 1]

The above settings can be arbitrarily set in accordance with the image characteristics and for creating a picture such as a special effect. The level difference (y−K) is stored in the ROM 7.
When P) is input as an address, a corresponding value is output. In the switch 13, the output of the comparator 6 is obtained, and when the input level y is smaller than the knee end point KE, the output of the look-up table is obtained. , And outputs the maximum value CL.

The multiplier 9 outputs the output of the switch 13 to (1-
k), and the adder 10 calculates the knee point K
The output from the multipliers 8 and 9 is added to P.
The switch 11 switches an input video signal or an output of the adder 10 under the control of the comparator 2. Next, the operation will be described.

The input level y of the video signal input from the input terminal 1 is compared with the knee point KP by the comparator 2 and with the knee curve end point KE by the comparator 6, respectively. When the input level y is smaller than the knee point KP (y <KP), the comparator 2 controls the switch 11, and the input video signal is output without being compressed.

When the input level y is larger than the knee point KP, the level difference detector 5 detects a level difference (y-KP) between the input level y and the knee point KP. The level difference (y-KP) is multiplied by k in the multiplier 8 and output to the adder 10 as shown in FIG. In ROM7,
The input level difference (y-KP) is converted based on the stored look-up table.

The switch 13 obtains the output of the comparator 6 and
When the input level y is lower than the knee end point KE, the output of the look-up table is output. When the input level y is higher than the knee end point KE, the maximum value CL is output. That is, when KP ≦ y <KE, the level difference (y−KP) input at the address is the data LT (y−KP) corresponding to the level difference (y−KP) as shown in Table 1.
−KP), and when the input level y is equal to or higher than the knee curve end point KE (y ≧ KE), the same value as the maximum value of the look-up table, that is, CL is output.

The output data of the switch 13 is output from the multiplier 9 to (1
-K) and is input to the adder 10. In the adder 10, the output of the multiplier 8, the output of the multiplier 9, and the knee point KP are added. Under the control of the comparator 2, the switch 11 switches the input level y if the input level y is smaller than the knee point KP, and switches the output of the adder 10 if the input level y is larger than the knee point KP. , And the output Y is obtained.

The above result can be expressed by the following equation. Y = y (however, y <K
Y = k · (y−KP) + (1−k) · LT (y−KP) + KP (However, when KP ≦ y <KE) Y = k · (y−KP) + (1 −k) · CL + KP (when y ≧ KE) With this configuration, the input level y of the video signal is in the range from the knee point KP to the knee curve end point KE, and the output level Y is as shown in FIG.
As in the case of k = 0.0 in (C), the compression characteristic is a smooth curve without a broken line, and does not generate a high frequency component. Therefore, a false image by the contour emphasizing circuit is applied to the video signal near the knee point KP. No contour occurs.

Further, the value is converted into a value corresponding to the level difference (y-KP) using a look-up table, and a value obtained by multiplying the converted value by (1.0-k) is a value obtained by a conventional compression method. (K · (y−KP) + KP)
The output level can be smoothly increased from the knee point KP to the knee curve end point KE easily by using one look-up table. If the value of the compression coefficient k is changed, the compression level can be set to a desired value. Even if the compression coefficient k is changed, the rate of increase at both ends of the predetermined range does not change, so that a smooth connection can be maintained. For example, when k = 0.8, k in FIG.
= 0.8, and when k = 0.3, k = 0.3
Characteristic.

Also, as shown in FIG. 3, if the range from the knee point KP to the knee curve end point KE is set to a narrow range, a smooth change near the knee point is maintained and then the knee circuit shown in FIG. The output characteristic can be close to the characteristic shown in FIG. 8, while, as shown in FIG. 4, if the predetermined range is expanded, the characteristic changes gradually and is emphasized. Can be set.

In a circuit such as that shown in FIG. 1 in which compression is performed in the range from the knee point KP to the knee curve end point KE using a look-up table, the capacity of the look-up table is as follows. Is determined by setting the range from to the knee curve end point KE. In the case of the present embodiment, the capacity can be as small as 128 words.

In the embodiment, the digital look-up table is used. However, the present invention is not limited to this. A non-linear circuit may be used instead of the look-up table, and the same effect is obtained. be able to.

[0035]

As described above, according to the present invention, the input
Increases smoothly and monotonically as the difference between the force level and the specified value increases
The value obtained by multiplying the value to be added by (1.0-k) is
Performs simple processing that only adds to the compressed value by the method
The output level smoothly as the input level increases.
Can be increased, and add two values separately
Thus, the compression coefficient k can be set within a range of 0 ≦ k <1.
By changing the setting, you can set the compression level to the desired value.
And maintain a smooth connection even if the compression coefficient k is changed.
You can have.

[0036]

When the input level of the video signal is less than the predetermined value , if the video signal is output at the same level as the input level, the video signal is output without the input level being compressed.
Furthermore, the smoothness increases as the difference between the input level and the predetermined value increases.
Value increases monotonically, and the rate of increase gradually increases with the increase in the difference.
If it is reduced to 0, the input rate at which the increase rate becomes 0
Above the bell, the output level increases as the input level increases
It increases smoothly and continuously.

[0038]

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a conceptual diagram of the present invention.

FIG. 3 is an explanatory diagram showing compression characteristics of the configuration of FIG. 1;

FIG. 4 is an explanatory diagram of the above.

FIG. 5 is a circuit diagram showing a conventional analog circuit.

FIG. 6 is an explanatory diagram of compression characteristics.

FIG. 7 is a circuit diagram showing a conventional digital circuit.

FIG. 8 is an explanatory diagram showing the compression characteristics of FIG. 7;

[Explanation of symbols]

 2,6 comparator 5 level difference detector 7 ROM 10 adder 11 switch

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/14-5/217

Claims (3)

(57) [Claims] An input level of a video signal is equal to or higher than a predetermined value.
Sometimes, the difference between the input level and the predetermined value is a compression coefficient k.
(0 ≦ k <1.0), the input level,
To a value that increases smoothly and monotonically as the difference from the predetermined value increases
A value obtained by multiplying (1.0−k) and the predetermined value are added.
A video signal output level of the video signal. 2. The system according to claim 1, wherein the input level of the video signal is less than the predetermined value.
2. The video signal compression method according to claim 1 , wherein the output is performed at a level equal to the input level when the video signal is full. 3. An increase in a difference between the input level and the predetermined value.
The value that increases smoothly and monotonically in accordance with
And the rate of increase gradually decreases to zero.
3. The video signal compression method according to 1 or 2 .