JPH0686096A - Production of gamma correction table - Google Patents

Abstract

PURPOSE:To provide a production method of a gamma correction table which can reduce the quantity of data on the test gamma correction value that are transferred to the gamma correction table from a control part and also can reduce the width of a transfer data bus. CONSTITUTION:The picture element data 104 outputted from an image pickup part 10 containing a CCD is converted into the digital picture element data 106 by an A/D converter 20. The data 106 is corrected by a gamma correction table contained in a gamma correction circuit part 30, and the corrected data 108 is stored in an IC memory card 50. A control part 40 controls the timing of the flow of those data and also transfers the test gamma correction value to the gamma correction table. Then the part 40 transfers only (m) less significant bits and produces more significant bits through the circuit 3 in order to reduce the width of a transfer data bus 200. Otherwise the part 40 performs the broken-straight line approximation and transfers a change point and the slope of each straight line to reduce the quantity of data to be transferred.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a gamma correction table used when performing non-linear correction of inverse characteristics on the image pickup device side in response to non-linearity of light emission characteristics of a picture tube of a receiver. It is a thing.

[0002]

2. Description of the Related Art The emission output L of a color picture tube is proportional to the signal voltage E raised to the power γ. Therefore, when the values of the light emission output L and the signal voltage E are represented by the logarithmic axis, the slope thereof is determined by the value of γ. This characteristic is the gamma characteristic, which is about γ = 2.2 in a color picture tube. Therefore, if the signal voltage proportional to the stimulus value of the subject obtained on the image pickup device side is directly displayed on the image receiver, when the signal level fluctuates, the non-linear characteristics of the picture tube distort the brightness, hue, and saturation for reproduction. Will be done. Therefore, it is necessary to perform the inverse characteristic nonlinear correction, and this is a process called gamma correction. It is economical to perform this gamma correction on the side of the image pickup device, and it is conventionally performed as such.

Even in an image pickup apparatus such as a digital electronic still camera, the gamma correction is performed when pixel data is stored in an image storage medium such as an IC memory card.

[0004]

However, in many cases, the type of solid-state image pickup device, for example, CCD, which is still used in the development stage of an image pickup device such as a digital electronic still camera, has not been determined. Therefore, there are cases where the CCD device itself is changed. In this way, when the CCD is changed, the gamma correction value is not always constant due to the characteristics of the CCD itself, and some correction is required. Therefore, at the development stage, the gamma correction table is
In many cases, instead of using a fixed table, data is transferred from a control unit such as a system controller to a memory area of a gamma correction table, and various gamma correction values are tested. In such a case, in order to improve the reproducibility in the intermediate gradation, gamma correction may be applied to image data having 1024 gradations of pixels, for example. At this time, a large amount of data for 1024 gradations must be set and transferred from the control unit to the gamma correction table memory by a 10-bit parallel data bus, which is difficult in terms of economical efficiency and work efficiency. There are challenges.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above drawbacks of the prior art and to provide a method for creating a gamma correction table in which the width of the data bus from the control unit or the amount of transferred data is reduced.

[0006]

In order to solve the above-mentioned problems, a method of creating a gamma correction table according to the present invention is a method of correcting gamma characteristics when correcting the gamma characteristics of a receiver by taking into consideration the input / output characteristics of the image pickup device. In a method of creating a gamma correction table that receives transfer information that uniquely defines a correction curve via a data bus and updates the gamma correction table, the data amount of the gamma correction curve is reduced, and the reduced data is transferred information. It is characterized in that each of the correction constants of the gamma correction table is generated and updated upon receiving this transfer information.

Further, in the method of creating the gamma correction table according to the present invention, when the gamma characteristic of the receiver is corrected in consideration of the input / output characteristic of the image pickup device, the transfer information which uniquely defines the gamma correction curve is transferred to the data bus. In the method for creating a gamma correction table for receiving the update via the gamma correction table, the lower m bits (m is a natural number smaller than n) of the gradation data of the signal expressed by a binary number of a natural number n bits are used as the transfer information. , Upper (n−m) bits are generated by using the change point of the most significant bit of the lower m bits in response to the transfer information, and gamma is generated based on the generated upper bits and lower m bits. It is characterized in that each correction constant in the correction table is updated.

Further, in the method of creating the gamma correction table according to the present invention, when the gamma characteristic of the receiver is corrected by taking into consideration the input / output characteristic of the image pickup device, the transfer information which uniquely defines the gamma correction curve is transferred to the data bus. In the method of creating a gamma correction table for receiving the via gamma correction table and updating the gamma correction table, when the gamma correction curve is represented by a two-dimensional plane and the X axis is the signal input level and the Y axis is the signal output level, a plurality of broken lines are drawn. Approximate with a straight line, the characteristic data of the linear equation with the signal input level of each straight line as a variable, and the intersection of each straight line are X
The change point represented by the coordinate on the axis is used as transfer information, and each correction constant of the gamma correction table is generated and updated based on this transfer information.

Further, in the method of creating the gamma correction table according to the present invention, when the gamma characteristic of the receiver is corrected in consideration of the input / output characteristic of the image pickup device, the transfer information which uniquely defines the gamma correction curve is stored in the data bus. In the method of creating a gamma correction table that receives via the, the gamma correction table, the signal output level difference value with respect to the signal input level between the ideal gamma correction curve and the actual gamma correction curve, and the signal input level On the other hand, one of the output level difference values between the straight line in which the signal output level is proportional and the actual gamma correction curve is used as transfer information, and each correction constant of the gamma correction table is generated and updated based on this transfer information. I am trying.

Further, in the method for creating a gamma correction table according to the present invention, any one of the above methods may be combined as transfer information, and each correction constant of the gamma correction table may be generated and updated based on this transfer information. .

[0011]

In the method of creating the gamma correction table according to the present invention, the data that uniquely defines the gamma correction curve is reduced, and this reduced data is used as the transfer information. The receiving side generates and updates each correction constant of the gamma correction table based on this transfer information.

Further, in the method of creating the gamma correction table according to the present invention, when the gradation of the signal is expressed by an n-bit binary number, the lower m bits are used as the transfer information from the control unit side.
The upper (n−m) bits are generated on the receiving side by using the change points of the most significant bits of the lower m bits, and each of the gamma correction tables is generated based on the generated upper bits and the received lower m bits. Update the correction constant.

Further, in the method of creating the gamma correction table according to the present invention, the gamma correction curve has the X-axis as the signal input level,
When represented by a two-dimensional plane with the Y-axis as the signal output level, approximation is made with a plurality of broken line straight lines, and the intersection of each broken line with the characteristic data of the linear equation with the signal input level of each straight line as a variable The change point of the input level represented by the axis coordinate is used as the transfer information. Based on this transfer information, each correction constant of the gamma correction table is generated and updated.

Further, in the method of creating the gamma correction table according to the present invention, the signal output level difference value with respect to the signal input level between the ideal gamma correction curve and the actual gamma correction curve, and the signal with respect to the signal input level. Either the output level difference value between the straight line to which the output level is proportional and the actual gamma correction curve is used as the transfer information. Based on this transfer information, each correction constant of the gamma correction table is generated and updated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for creating a gamma correction table according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration block diagram showing an embodiment of a method of creating a gamma correction table of the present invention. FIG. 2 is a transfer circuit diagram showing an example of a high-order 2 bit generation circuit of the gamma correction table in the same embodiment.

Referring to FIG. 1, the test apparatus 1 for creating a gamma correction table is controlled by a control unit 50 to output a one-shot image pickup output signal from an image pickup unit 10 of a digital electronic still camera using a CCD, for example. For each time, various gamma corrections are performed by the gamma correction circuit unit 30 variably set by the control unit 40 described later, and the corrected pixel data is stored in a storage medium such as the IC memory card 50. is there. In the figure, functions that are not directly related to the understanding of the present invention are omitted. This IC memory card 50
It is mounted on an image reproducing device (not shown). The operator can determine the optimum gamma correction value by inspecting the image reproduced on the image reproducing device.

The apparatus 1 is provided with a digital electronic still camera image pickup section 10 provided with an all-pixel readout interline CCD in which a vertical CCD having the same number of pixels as the photodiodes is arranged in the first stage. This image pickup unit 10 is based on a shutter opening / closing command 100 from a control unit 40 described later.
For example, an image of a test pattern such as grayscale or Barbara is imaged, and the charge proportional to the amount of light reflected from the subject is CCD.
Is an image pickup unit that transfers the electric charge stored in the CCD to a voltage level based on a read clock signal 102 from the control unit 40 described later. The output circuit 104 of the image pickup unit 10 is connected to the A / D converter 20. A / D
The converter 20 is a circuit unit for converting the input analog voltage level pixel data 104 into a digital signal (10 bits) with a maximum of 1024 gradations in this embodiment. The output circuit 106 of the A / D converter 20 is connected to the gamma correction circuit unit 30.

The gamma correction circuit section 30 has a look-up table storage area for storing gamma correction data, which is composed of, for example, an S-RAM (not shown). The gamma correction circuit unit 30 is a circuit unit that performs gamma correction on the digitally converted pixel data 106 input from the A / D converter 20 by table conversion. The gamma-corrected pixel data 108 is output from the gamma-correction circuit unit 30. The pixel data 108 is stored in, for example, the IC memory card 50 according to an address signal 110 output from the control unit 40 described later. The IC memory card 50 is detachably attached to the apparatus 1. After the imaging test, the IC memory card 50 is removed from the apparatus 1 and attached to a reproduction device (not shown) so that the operator can perform gamma correction. Used for inspection of effectiveness.

The control unit 40 is a control unit for supplying the gamma correction information 200 to the gamma correction circuit unit 30 through the data bus 200. This supply is performed by the operator by the control unit at the timing of turning on the power and the timing of the shutter opening / closing command 100.
It is done by 40 operations. The operator is the gamma correction information
Since the correction value of 200 can be changed on a trial basis by the operation from the control unit 40, it is possible to find the optimum gamma correction value. The control unit 40 is also a control unit that supplies a read clock signal 102 to the digital electronic still camera imaging unit 10 and an address signal 110 to the IC memory card 50. The control unit 40 sends these signals to the shutter opening / closing command 10
After sending 0, it is sent to each unit under constant timing control, and the reading of the pixel data 104 from the image pickup unit 10 and the sending of the address signal 110 to the IC memory card 50 are synchronized.

FIG. 2 is an example of a circuit for creating a gamma correction curve in this embodiment. In addition, in this specification, the term "curve" is to be interpreted in a broad sense including a straight line. The maximum digital pixel data of the present invention is 1024.
Since the gradation is used, when the gamma correction data is transferred in parallel from the control unit 40 to the gamma correction circuit unit 30, originally, a 10-bit data bus and one strobe signal line should be required. However, in this embodiment, the width of the data bus 200 is reduced to 8 bits, and the lower 8 bits of information are transferred to the data bus 20.
0 for transfer, and gamma correction circuit for upper 2 bits
I'm taking the method of generating at 30. More specifically, the control unit
40 has an output buffer circuit 41, which, in addition to forward the 2 ^{0-2 7} signals in parallel as data bits of the strobe signal 201, a gamma correction circuit unit 30, determines a state change of normally 2 ⁷ bits To do. This utilizes the fact that the so-called gamma correction curve always rises as the gradation of the input data rises. Therefore, the gamma correction information 200 is transferred in order from the lower gradation of the input data, and finally the information of 1024 gradations is transferred by the lower 8 bits.

The generation of the upper 2 bits is performed by the counters 43 and 44 which are composed of two JK flip-flops, for example. The clock input CK1 of the counter 43 is connected to two ^7-bit line 209, the clock CK2 of the counter 44
Is connected to the Q output of the counter 43. Counter 4
The respective J and K inputs of 3, 44 are fixed to the power supply level, that is, "H" level. The Q output of the counter 43 is also output as a 2 ⁸ signal. The Q output of the counter 44 is output as a 2 ⁹ signal. The reset R of the counters 43 and 44 is performed by the first strobe signal of transfer and power-on. The reset circuit is omitted because it is not particularly relevant to understanding the invention.

FIG. 3 is a diagram showing changes in received data including transfer data and additional bits. Referring to FIG. 3, the 1024th gradation of the transfer information is represented by a decimal value of 10
23. Therefore, the 2 ⁷ bit rises to “1” and then falls to “0” three times between 0 and 1023. The counter 43 inputs the falling edge of 2 ⁷ as the clock CK1. Counter 44, counter 43
Input the falling edge of Q output as clock CK2. The counter 43 has the J input and the K input fixed to the “H” level, so that the counter 43 receives the first clock CK1.
The Q output of 43 becomes "H". The J and K inputs of the counter 44 are fixed to the "H" state. At this time, the Q output of the counter 44 is still "L". Therefore, that is, when the first clock is input, 2 ⁸ bits are "1", 2
^{The 9th} bit holds the state of "0".

When the second clock CK1 is input, since the J and K inputs of the counter 43 are always in the "H" state, they are inverted by the clock CK1 input and the Q output of the counter 43 is inverted to the "L" state. By the falling edge of the clock CK2 of the counter 44, which receives the Q output of the counter 43,
The Q output of the counter 44 is inverted to the "H" state. That is, in the 2 ^8-bit second time clock CK1 input "0",
2 ⁹ bits will retain the state of "1".

When the clock CK1 is input for the third time, the Q output of the counter 43 becomes "H" again. At this time, the clock of the counter 44 that receives the Q output of the counter 43 as an input
Since CK2 does not fall, the Q output of the counter 44 does not change and maintains the "H" state. That is, 2 ^8-bit three time clock CK1 input "1", 2 ⁹ bit will retain the state of "1".

This will be described with reference to FIG. 4. A curve 300 represents a gamma correction curve to be transferred from the control section 40 to the gamma correction circuit section 30 and stored in the memory area as a look-up table. However, since the width of the data bus has been reduced from 10 bits to 8 bits, it is not possible to transfer numbers of 256 or more as they are. Therefore, the information of 2 ⁸ and 2 ⁹ is not transferred and 2 ⁰
8 bits of information up to 2 ⁷ are transferred. The transfer starts from the lower input level. First, the curve 301 rises with the input level, and the output level exceeds 2 ⁰
As for the contents of ~ 2 ⁷ , the output level drops to 0 or close to 0. At this time, the 2 ⁷ bit changes from "1" to "0" and the clock CK1 is input to the counter 43 (2 ⁷ bit becomes "1" when the value is 128 or more). Then, the curve 302 rises with the input level and again falls near 0 at point B to generate the second clock CK1. Similarly, C of curve 303
The third clock CK1 is generated at the point. Also, curve 304
Becomes forward ends at point D, by the contents of the 2 ^{0-2 7} becomes 0, actually generates a fourth time clock CK1. This clock causes counters 43 and 44 to overflow to the same reset state.

When the gamma correction circuit section 30 receives the information of the curves 301 to 304 in this way, it adds the upper 2 bits generated by the counters 43 and 44, so that each curve is translated in the ascending direction. Become. As a result, the curve 300 is generated and stored in the memory area as a look-up table.

According to the present embodiment, 10 data buses should be required to transfer information for 1024 gradations, but a simple counter is provided in the gamma correction circuit section 30 on the receiving side. By providing them, the data bus can be reduced to eight.
Furthermore, the gamma correction curve can be arbitrarily set by the control unit 40,
Since this is transferred to the gamma correction circuit unit 30 and the look-up table is updated, an image that has been subjected to optimum gamma correction in consideration of the characteristics of the imaging unit 10 can be obtained.

Next, another example of creating a gamma correction curve will be described with reference to FIG. FIG. 5 is a diagram in which the gamma correction curve is approximated by a broken line. In FIG. 5, for example, a broken line using four straight lines is used for approximation. Even if such a broken line is used, a relatively accurate approximation of the gamma correction curve can be obtained. In the example of performing this polygonal line approximation, the control unit 40
Is connected to an input device (not shown) such as a digitizer or a mouse. The operator inputs the intersections of the adjacent straight lines in FIG. 5 as the change points from this input device. In the example of FIG. 5, (x _1, y ₁ ), (x ₂ , y ₂ ), (x
_3, y ₃ ) is the change point.

When the change point is given, the control unit 40 next calculates the characteristic data of each straight line represented by the linear equation. The slope of the straight line as this characteristic data is the straight line 402
For example, it can be expressed as (y ₂ −y ₁ ) / (x ₂ −x ₁ ). The control unit 40 calculates this slope for each straight line, and when the result is represented by, for example, fixed point data, divides it into an integer part and a part below the decimal point. After the above calculation, the control unit 40 represents the change point on the X axis of FIG. 5 (x _1,
x ₂ , x ₃ ) and the integer and fractional parts that represent the slope of each straight line, and generate a transmission format that
It is transferred to the gamma correction circuit unit 30 via 0. When receiving the data, the gamma correction circuit unit 30 cumulatively adds the slopes of the respective straight lines for each gradation from 1 gradation of the input signal gradation to 1024 gradations. That is, at the time of this cumulative addition, X in FIG.
The slope of the straight line changes each time the input gradation exceeds the input value (x _1, x ₂ , x ₃ ) representing the change point on the axis. Therefore, the output signal after gamma correction along the broken straight line in FIG. 5 can be created by cumulatively adding the slopes of the straight lines for each gradation from the 1st gradation to the 1024 gradations. This data is stored in the memory area as a lookup table.

In this preparation example, the gamma correction curve along the broken line is obtained by cumulatively adding the slopes of the respective straight lines in the gamma correction circuit 30 in this way, but the method is not necessarily limited to the cumulative addition. , You may proceed as follows. Referring to FIG. 5, as described above, 4
The gamma correction curve is represented by the broken line of the book. Therefore, a Y-intercept where the extension line of each straight line intersects the Y-axis is obtained. In the figure, the Y-intercept of the straight line 404 is Y ₃ , and the Y-intercept of the straight line 403 is Y.
The intercept is Y ₂ and the Y intercept of the straight line 402 is Y ₁ , and the straight line 401
Y intercept of is 0 (origin). Further, according to the figure, (x _1, y ₁ ), (x ₂ , y ₂ ), and (x _3, y ₃ ) are set and input at the intersections of the adjacent straight lines. Next, the slope of each straight line is obtained. This can be represented by (y ₂ −y ₁ ) / (x ₂ −x ₁ ), for the straight line 402, as described above. The control unit 40 calculates the inclination and the Y intercept for each straight line. When the slope is expressed by fixed point data, for example, it is divided into an integer part and a part below the decimal point. After the above calculation, the control unit 40 represents the change point on the X axis of FIG.
(x _1, x ₂ , x ₃ ), an integer part and a decimal part representing the slope of each straight line, and a Y-intercept (0, Y _1, Y _2, Y ₃ ) of each straight line, and generate a transmission format. The data is transferred to the gamma correction circuit unit 30 via the data bus 200. Gamma correction circuit section 30
Receives the data, the linear equation of each line Y = a _n
X + b _n is obtained from the slope (a _n ) and the Y intercept (b _n ). The gamma correction circuit unit 30 sets each input gradation represented by the X axis to 0 in the linear equation Y = a _n X + b _n of each of four straight lines.
To x ₁ , x ₁ to x ₂ , x ₂ to x ₃ and x ₃ to 1023 in this order 4
The value of each Y is calculated by substituting it into X of one linear equation. That is, the straight line 401 is between 0 and x ₁ , the straight line 402 is between x ₁ and x ₂ , the straight line 403 is between x ₂ and x ₃ , and the x ₃ through 10
Between 23, the straight line 404 is used to calculate each output gradation (Y value) for each input gradation. This calculation result represents the output signal after gamma correction along the broken line. This data is stored in the memory area of the lookup table. In this example of the creation, the number of broken line straight lines was set to 4 straight lines of 3 change points, and the gamma correction curve approximation was performed. May be

According to the present embodiment, it is only necessary to input the change point when changing the gamma correction value, the operation becomes very easy, and the amount of information transferred via the data bus 200 can be greatly reduced. .

Next, a third correction curve generation example will be described with reference to FIGS. 6 and 7. 6 and 7 show characteristic curves of gamma correction in which the horizontal axis represents the input gradation of digital pixel data and the vertical axis represents the output gradation. In FIG. 6, a curve 501 is an ideal gamma correction characteristic curve (gamma value
Curve 502 indicates the gamma correction curve created by the control unit 40 in consideration of the input / output characteristics of the CCD mounted on the imaging unit 10. The control unit 40 calculates the difference value between the output gradation curves 501 and 502 for each input gradation. This difference value is stored in the data bus 20 together with the sign bit.
It is transferred to the gamma correction circuit section 30 via 0 in order from the one having the lowest input gradation. The gamma correction circuit unit 30 previously stores data of an ideal gamma correction characteristic curve in a storage table (not shown). The gamma correction circuit unit 30 adds the difference value data with the sign (positive and negative polarities) transferred from the control unit 40 to the data of the ideal gamma correction characteristic curve in order from the one having the lowest input gradation to perform the gamma correction. Reproduce the curve 502 on the circuit section 30 side. The lookup table is updated with this reproduction data. Originally, the input / output characteristics of CCD are 1: 1
The difference value data between the curve 501 and the curve 502 is not so different, and it is sufficient that there are 8 data bits in addition to the sign bit.

In FIG. 7, a straight line 601 indicates (output gradation)
/ (Input gradation) is a straight line represented by 1/1. A curve 602 is a gamma correction curve created by the control unit 40 by adding the input / output characteristics of the CCD mounted on the imaging unit 10 to the ideal gamma correction characteristic curve like the curve 502 of FIG. There is. The control unit 40 calculates the difference value between the output gradation curve 602 and the straight line 601 for each input gradation. The gamma correction curve 602 always takes a value larger than that of the straight line 601 for each input gradation. Therefore, in this case, the difference value data without the sign bit is transferred to the gamma correction circuit unit 30 via the data bus 200 in order from the one having the lowest input gradation. The gamma correction circuit unit 30 sets the difference value data transferred from the control unit 40 in order from the one with the lowest input gradation.
Add the value to the input gradation value and set the curve 60 on the gamma correction circuit 30 side.
Reproduce 2. The lookup table is updated with this reproduction data. In this case, the difference value data is the number of gradations.
Even if it exceeds 256 gradations, it does not exceed 511 gradations. Therefore, a bus width of the data bus 200 of 9 bits is sufficient.

According to the present embodiment, in both FIG. 6 and FIG. 7, if the bus width of the data bus 200 is 9 bits, the data transfer will not be hindered, and the bus width of 10 bits conventionally required. Can be reduced to 9 bits. Further, the input / output characteristics that change subtly in a dark area having a low input gradation can be dealt with by operating the difference value in the control section 40.

Next, an example of the fourth producing method will be described with reference to FIG. This example is based on a combination of the first example and the second example, or the third example and the second example, as shown in FIG. That is, as seen in FIG. 8, the dark portion, that is, the change point of the image with low input gradation
Below x ₁ , there are cases in which the input / output relationship changes with a certain function that cannot be expressed. In this case, for example, when the input gradation is between 0 and x ₁ , the data of each output gradation corresponding to each input gradation, as described in the first preparation example, or as described in the third preparation example. In addition, difference value data of each output gradation corresponding to each input gradation is created by the control unit 40 and transferred by the data bus 200. After the input gradation exceeds x ₁ , the same operation as the operation described in the second creation example is performed, and the inclination and change point of each straight line are created by the control unit 40 and transferred by the data bus 200.

According to this example, the output gradation can be finely set in the dark portion where the input gradation is low, and the output gradation is approximated by a monotonous broken line in the portion where the input gradation is higher than that. The data of a good gamma correction curve can be transferred to the gamma correction circuit unit 30 with a small transfer data amount.

[0037]

As described above, according to the present invention, the data that uniquely defines the gamma correction curve is reduced, and the reduced data is used as the transfer information. The receiving side generates and updates each correction constant of the gamma correction table based on this transfer information. Therefore, there is an effect that the data bus can be reduced or the amount of information transferred via the data bus can be greatly reduced. Also, when the present invention is applied for testing,
It is possible to expect an advantageous effect that the setting operation can be easily performed while improving the accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a test apparatus that realizes a gamma correction table creating method of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a circuit that creates upper 2 bits of transfer information in the embodiment shown in FIG.

FIG. 3 is a diagram showing a method of creating upper 2 bits of the transfer information shown in FIG.

FIG. 4 is a diagram showing a gamma correction characteristic curve when the upper 2 bits of the transfer information shown in FIG. 2 are added.

FIG. 5 is a diagram showing a gamma correction characteristic curve by polygonal line approximation in the embodiment.

FIG. 6 is a diagram showing a difference value between an actual gamma correction characteristic curve and an ideal gamma correction characteristic curve in the embodiment.

7 is a diagram showing a difference value between an actual gamma correction characteristic curve and a straight line when the ideal gamma correction characteristic curve is replaced with a straight line in FIG.

FIG. 8 is a diagram showing a gamma correction characteristic curve by combination in the embodiment.

[Explanation of symbols]

 1 Test equipment 10 Digital electronic still camera Imaging section 20 A / D converter 30 Gamma correction circuit section 40 Control section 50 IC memory card

Claims (5)

[Claims] 1. A gamma correction table is updated by receiving via a data bus transfer information that uniquely defines a gamma correction curve when the gamma characteristics of a receiver are corrected in consideration of the input / output characteristics of the image pickup device. In the method of creating the gamma correction table, the data amount of the gamma correction curve is reduced,
A method of creating a gamma correction table, wherein the reduced data is used as the transfer information, and each correction constant of the gamma correction table is generated and updated in response to the transfer information. 2. The gamma correction table is updated by receiving, via a data bus, transfer information that uniquely defines a gamma correction curve when the gamma characteristic of a receiver is corrected in consideration of the input / output characteristics of the image pickup device. In the method of creating the gamma correction table, the lower m bits (m is a natural number smaller than n) of the gradation data of the signal expressed by a binary number of a natural number n bits are used as the transfer information, and the upper (n−m) bits are ,
Receiving the transfer information, it is generated using the change point of the most significant bit of the lower m bits, and each correction constant of the gamma correction table is updated based on the generated upper bit and the lower m bits. A method for creating a gamma correction table, which is characterized in that 3. The gamma correction table is updated by receiving, via a data bus, transfer information that uniquely defines a gamma correction curve when correcting the gamma characteristic of a receiver by taking into consideration the input / output characteristics of the image pickup device. In the method of creating the gamma correction table, when the gamma correction curve is represented by a two-dimensional plane and the X-axis is the signal input level and the Y-axis is the signal output level, approximation is performed with a plurality of broken line straight lines and the signal input of each straight line is performed. Characteristic data of a linear equation having a level as a variable and a change point in which the intersection of each straight line is represented by coordinates on the X axis are used as the transfer information, and each correction constant of the gamma correction table is generated based on the transfer information. A method for creating a gamma correction table, which is characterized by updating and updating. 4. A gamma correction table is updated by receiving via a data bus transfer information that uniquely defines a gamma correction curve when the gamma characteristic of a receiver is corrected by taking the input / output characteristics of the image pickup device side into consideration. In the method of creating a gamma correction table, the signal output level difference value with respect to the signal input level between the ideal gamma correction curve and the actual gamma correction curve, and the straight line where the signal output level is proportional to the signal input level Of the output level difference value from the gamma correction curve of 1. above is used as the transfer information, and each correction constant of the gamma correction table is generated and updated based on the transfer information. 5. The method according to any one of claims 2 to 4, wherein the gamma correction table according to any one of claims 2 and 4 is used for a portion of a signal input level that is lower than a predetermined gradation. Any one of the correction table creation methods is applied, and the gamma correction table creation method according to claim 3 is applied to a portion of the signal input level that exceeds the predetermined gradation to obtain the transfer information. A method of creating a gamma correction table, characterized in that each correction constant of the gamma correction table is generated and updated based on transfer information.