JPH06189160A - Digital gamma correcting device - Google Patents

Abstract

PURPOSE:To provide the gamma correcting device having a characteristic approximating an ideal curve with small circuitry. CONSTITUTION:An inputted digital input signal 2 is supplied to a level detector 3, and a multiplication coefficient 4 and an addition coefficient 5 are respectively supplied to a multiplier 6 and an adder 8. After the multiplication coefficient 4 is multiplied to the digital input signal 2 by the multiplier 6, the addition coefficient 5 is added by the adder 8 to obtain a polygonal line gamma correcting signal 9. When the digital input signal 2 is close to a break point, a correction coefficient 15 is obtained by multiplying a correcting signal 13 from a table 11 for correcting signal generation and a multiplication coefficient 12 with a multiplier 14. The polygonal line gamma correcting signal 9 and the correction coefficient 15 are added by an adder 16, and a gamma correcting signal 17 having the characteristic approximated to the ideal curve is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital gamma correction device for performing gamma correction on a digital video signal converted from an analog signal output from a solid-state image pickup device.

[0002]

2. Description of the Related Art A digital gamma correction device used in a conventional digital camera will be described with reference to FIGS.

FIG. 2 shows a digital gamma correction device using only a ROM / RAM table. In FIG. 2, the digital input signal 32 is transferred to the ROM / RAM via the input terminal 31.
It is supplied as the address of the table 33. ROM / R
The AM table 33 has an input / output characteristic of a gamma characteristic, and outputs the gamma correction data 34 according to the digital input signal 32 supplied as an address to the output end 35.

In such a gamma correction device, the gamma characteristic can be freely set, but in order to improve the resolution (gradation characteristic) of the camera, the digital signal 32 and the gamma correction data 34 are made multi-bit. Need to RO
There is a problem that the circuit scale of the M / RAM table 33 becomes large. In addition, there is a problem in that the resolution of the camera is affected because speeding up is difficult.

FIG. 3 shows a polygonal line gamma correction apparatus having one multiplier and one adder. Such a polygonal line gamma correction device is disclosed in JP-A-4-18865 and JP-A-4-4-2.
It is disclosed in Japanese Patent No. 3569 and Japanese Patent Laid-Open No. 4-23570. In FIG. 3, the input signal 42 is supplied to the coefficient generation circuit 43 and the multiplier 45 via the input end 41. The coefficient generation circuit 43 creates a multiplication coefficient 44 corresponding to the input signal 42 and outputs it to the multiplier 45, and also creates an addition coefficient 46 corresponding to the input signal 42 and outputs it to the adder 47. The multiplier 45 outputs a signal obtained by multiplying the input signal 42 and the multiplication coefficient 44 to the adder 47. The adder 47 adds the output of the multiplier 45 and the addition coefficient 46, and outputs the gamma-corrected signal to the output end 48. Next, a more detailed description will be given with reference to FIG. 4 showing the input / output characteristics of this polygonal line gamma correction device.

The input / output characteristic shown in FIG. 4 is called a polygonal line gamma, and in this embodiment, the multiplication coefficient 44.
The case where there are three combinations of and the addition coefficient 46 will be described. The more combinations of the multiplication coefficient 44 and the addition coefficient 46, the closer to the ideal gamma curve. The input signal 42 of the coefficient generation circuit 43 is from A to
Between B, the multiplication coefficient = K, addition coefficient = 0, between B and C, multiplication coefficient = K / 2, addition coefficient = D1, and when larger than C, multiplication coefficient = K / 4, addition coefficient = D2. It outputs to the multiplier 45 and the adder 47, respectively. As a result, the input / output characteristic of this polygonal line gamma becomes as shown by the polygonal line characteristic 41.

Such a gamma correction device has a multiplication coefficient of 44
Although the more the number of combinations of the addition coefficient 46 and the addition coefficient 46 is increased, the closer to the ideal gamma curve can be obtained, but in order to do so, the coefficient generation circuit 43 becomes complicated and the circuit scale becomes large. . On the contrary, when the number of types of combinations is reduced, it is advantageous in terms of circuit scale and speed compared with the table method described in FIG. 2, but accurate gamma correction is performed because a difference from the ideal curve occurs before and after the break point. There is a problem that you can not. Also,
There is a problem that a sharp change in the characteristics at the break point appears in the image and the image quality deteriorates.

[0008]

As described above, in the conventional gamma correction apparatus, when only the ROM / RAM table is used, it is necessary to increase the number of bits in order to improve the resolution (gradation characteristics) of the ROM. There is a problem that the circuit scale of the / RAM table increases. In addition, there is a problem that speeding up is difficult.

Further, in a general polygonal line gamma correction device,
Although reducing the number of break points is advantageous in terms of circuit scale and speeding up, there is a problem in that the difference from the ideal curve becomes large and a sharp change before and after the break point deteriorates image quality. It was Further, when the number of break points is increased to approximate the ideal curve, there is a problem that the circuit scale of the coefficient generation circuit becomes large.

An object of the present invention is to provide a gamma correction device which eliminates the above-mentioned drawbacks of the prior art and can obtain a gamma correction device having a characteristic close to an ideal curve with a small circuit scale. .

[0011]

In order to achieve the above object, in the present invention, a level detecting means for detecting the level of an input video signal, and a predetermined level according to the detection level of the level detecting means. A coefficient output means for outputting a multiplication coefficient and an addition coefficient, a multiplication means for multiplying the video signal by the multiplication coefficient, a polygonal line for adding the output of the multiplication means and the addition coefficient, and outputting a polygonal line gamma correction signal. When the level of the video signal is within a predetermined range before and after a change level at which the multiplication coefficient and the addition coefficient change, a gamma correction means and a predetermined correction signal according to a level difference from the change level are provided. A digital gazer comprising: a correction signal output means for outputting; a polygonal line gamma correction means; and an addition means for adding the outputs of the correction signal output means. To provide between correction device. Also, the correction signal output means is a ROM (or RAM) table, and a digital gamma correction device is provided.

Also, the coefficient output means has a plurality of change levels, and the correction signal output means uses the same ROM (or RAM) table data at the plurality of change levels. I will provide a.

Further, the coefficient output means has a plurality of change levels, and the correction signal output means uses the same ROM (or RAM) table data for the plurality of change levels, and the position of the table data and the change level. There is provided a digital gamma correction device, characterized in that the correction signal is obtained by multiplying by a multiplication level according to.

[0014]

With this structure, the multiplication coefficient and the addition coefficient are obtained according to the level of the input video signal. The input video signal is multiplied by the multiplication coefficient, and this signal and the addition coefficient are added to obtain a polygonal line gamma correction signal. Also,
When the input video signal is around the change level, a correction signal is obtained according to the level difference from the change level, and the correction signal and the polygonal line gamma correction signal are added to obtain a gamma correction device close to an ideal curve. it can. Also,
The circuit scale can be further reduced by using a common circuit for correction before and after the break point.

[0015]

Embodiments of the present invention will be described in detail below with reference to FIG.

FIG. 1 is a diagram showing the construction of a gamma correction apparatus showing an embodiment of the present invention. In FIG. 1, a digital input signal 2 is supplied to a level detector 3 and a multiplier 6 via an input terminal 1. The level detector 3 detects the level of the input digital input signal and outputs the multiplication coefficient 4 and the addition coefficient 5 corresponding to the detected level to the multiplier 6 and the adder 8, respectively.

The multiplier 6 multiplies the input digital input signal by the multiplication coefficient 4, and outputs the multiplication signal 7 as the multiplication result to the adder 8. The multiplication signal 7 becomes a signal having an inclination according to the multiplication coefficient 4. The adder 8 adds the multiplication signal 7 and the addition coefficient 5, and outputs the polygonal line gamma correction signal 9 obtained by the same method as the conventional technique to the adder 16. In addition, the level detector 3 includes, before and after the break point of the input digital input signal, an address signal 10 indicating before and after the break point, a multiplication coefficient 12 having information indicating which break point, and a correction signal generation table 11. And to the multiplier 14, respectively. The correction signal generation table 11 outputs the correction signal 13 corresponding to the address signal 10 to the multiplier 14. The correction signal generating table 11 is a ROM / RAM table, but it is small in scale as compared with a conventional gamma correction device using only a ROM / RAM table, as it only needs to have a table around the break points. . The multiplier 14 multiplies the correction signal 13 by the multiplication coefficient 12, and outputs the correction coefficient 15 as a result of the multiplication to the adder 16. The adder 16 adds the polygonal line gamma correction signal and the correction coefficient 15 and outputs a smooth gamma correction signal 17 close to an ideal curve to the output end 18.

In this way, the correction signal generation table 11
Since it suffices to output the correction signal only for the input level near the break point, the circuit scale can be reduced.

Further, the correction signal generating table 11 can be used in common even if the multiplication coefficient 4 and the addition coefficient 5 change at different bending points, whereby the circuit scale can be further reduced. At this time, the correction amount can be optimized by changing the multiplication coefficient 12. Also,
If the scale of the correction signal generation table 11 is considerably small, it may be replaced with a corresponding generation circuit.

[0020]

According to the present invention, a large-scale ROM / R can be used.
Without using the AM table, it is possible to obtain a gamma correction device having a small circuit configuration and a high speed and close to an ideal curve.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a gamma correction device according to the present invention.

FIG. 2 is a diagram showing a configuration of a conventional gamma correction device.

FIG. 3 is a diagram showing a configuration of another conventional gamma correction device.

FIG. 4 is a diagram showing a correction waveform for polygonal line gamma correction.

[Explanation of symbols]

1 ... Input end, 2 ... Digital input signal, 3 ... Level detector, 4, 12 ... Multiplication coefficient, 5 ... Addition coefficient, 6, 14 ... Multiplier, 7 ... Multiplication signal, 8, 16 ... Adder, 9 ... Polygonal line gamma correction signal, 10 ... Address signal, 11 ... Correction signal generation table, 13 ... Correction signal, 15 ... Correction coefficient, 17
... Gamma correction signal, 18 ... Output end.

Claims (4)

[Claims] 1. A level detection means for detecting the level of an input video signal, a coefficient output means for outputting a predetermined multiplication coefficient and addition coefficient according to the detection level of the level detection means, the video signal and the Multiplication means for multiplying a multiplication coefficient; a polygonal line gamma correction means for adding the output of the multiplication means and the addition coefficient to output a polygonal line gamma correction signal; and a level of the video signal in which the multiplication coefficient and the addition coefficient Is within a predetermined range before and after the change level, which is a changing level, a correction signal output means for outputting a predetermined correction signal according to a level difference from the change level, the polygonal line gamma correction means, and the correction signal output. A digital gamma correction device comprising: an addition unit that adds the outputs of the units. 2. The digital gamma correction apparatus according to claim 1, wherein the correction signal output means is a ROM (or RAM) table. 3. The coefficient output means has a plurality of change levels, and the correction signal output means uses the same ROM (or RAM) table data for the plurality of change levels. The digital gamma correction device according to the item. 4. The coefficient output means has a plurality of change levels, and the correction signal output means uses the same ROM (or RAM) table data for the plurality of change levels.
The digital gamma correction apparatus according to claim 1, wherein the correction signal is obtained by multiplying the table data by a multiplication level corresponding to the position of the change level.