JP3387177B2 - Shading correction circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device having a plurality of pixels arranged in a matrix.

[0002]

2. Description of the Related Art Conventionally, an image pickup output signal obtained from an image pickup device is accompanied by shading which is caused by various causes such as sensitivity unevenness of the image pickup device and influence of dark current, that is, distortion of light and darkness over a relatively wide range of the screen. It has been known. For example, charge coupled devices (CCD)
In the solid-state imaging device such as a CCD imaging device formed by an ed device), an image sensor that employs various methods such as a frame transfer type, an interline transfer type, and a frame interline transfer type as a signal charge transfer method is provided. However, in each of them, the signal charges of a plurality of pixels arranged in a matrix are transferred in the vertical direction and sequentially read out one horizontal line at a time during one horizontal scanning period through the horizontal transfer register. Since the image pickup output signal is obtained by reading out the signal charges of all pixels for one screen in the period, a dark current proportional to the time of transfer to the horizontal transfer register is added to the signal charges, This dark current causes a sawtooth-like luminance change in one vertical scanning period, that is, causes shading in the vertical direction. . In addition, the dark current in the horizontal transfer register causes a sawtooth-like luminance change in one horizontal scanning period, that is, horizontal shading.

In general, the shading includes white (modulation) shading in which the output is small in the peripheral portion of the screen,
There is black (superimposed) shading in which the black level is not uniform over the screen. The shading correction processing is performed by mixing the shading correction signal with the imaging output signal in an analog manner by a multiplier for white shading and an adder for black shading. The shading correction signal is formed by creating a sawtooth wave signal and a parabolic wave signal in both horizontal and vertical directions and synthesizing them.

In the conventional shading correction circuit, the output levels of the signal generators of the sawtooth wave signal and the parabolic wave signal can be variably adjusted by a manual operation with a level adjuster such as a volume. In order to perform processing, the output level of each of the signal generators is manually adjusted while watching the waveform monitor.

Further, in a three-plate type color image pickup device in which color components of a subject image are separated into, for example, a red component, a green component, and a blue component, and images of each color component are individually picked up by three image pickup elements, Shading correction processing is performed for each of the image pickup devices.

[0006]

By the way, in the conventional shading correction circuit, the output levels of the respective signal generators of the sawtooth wave signal and the parabolic wave signal are checked while observing the waveform monitor so that the proper shading correction processing is performed. Since the adjustment was performed manually, it is necessary to perform the adjustment work over time in order to perform the adjustment accurately. In addition, skill is required for the adjustment work. Particularly, in the three-plate color image pickup device, it is necessary to perform the shading correction process for each of the image pickup devices, and there is a problem that the adjustment work requires a great deal of labor and time.

Therefore, in view of the above-mentioned problems of the shading correction circuit, the applicant of the present invention uses a black shading correction circuit in a shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device in which a plurality of pixels are arranged in a matrix. Forming horizontal and vertical shading correction data required for shading correction from the imaging output signal obtained by the image sensor for the purpose of enabling quick and appropriate correction processing and white shading correction processing. Then, the shading correction data is read from the storage means during the actual image pickup operation, and black shading correction and white shading correction are automatically performed on the image pickup output signal of each image pickup element based on the shading correction data. Shading Provided a positive circuit (JP-A-3-26
2282).

By the way, in the above shading correction circuit, in the process of forming horizontal and vertical shading correction data necessary for shading correction from the image pickup output signal obtained by the image pickup device, the random noise component superimposed on the image pickup output signal is added. Is large, the shading component and the random noise component cannot be separated, and the shading correction data including the random noise component is formed. When black shading correction data or white shading correction is applied to the image pickup output signal of the image pickup device based on this shading correction data, random noise appears as fixed pattern noise, resulting in unsightly image output. Is desired.

Further, in the case where the shading correction error is detected by the least square method or the like in the image output signal which has been subjected to the shading correction processing, when the random noise component superimposed on the image output signal is large, the shading component and the random noise component are included. Cannot be separated, and a shading correction error in a state where a random noise component is included will be detected. Therefore, it is desired to improve the point that the shading correction error changes due to the random noise level and the accurate shading correction error cannot be detected.

In view of the problems of the conventional shading correction circuit as described above, the present invention provides a shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device having a plurality of pixels arranged in a matrix. An object of the present invention is to provide a shading correction circuit capable of detecting an accurate shading correction error for the purpose of quickly and properly performing black shading correction processing and white shading correction processing.

[0011]

A shading correction circuit according to the present invention is a shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device having a plurality of pixels arranged in a matrix. And an analog / digital converter for digitizing the image pickup output signal of the image pickup device, and an image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter in a state where no light is incident on the image pickup surface of the image pickup device. First correction data forming means for integrating level data in the horizontal and vertical directions to form first and second shading correction data according to the horizontal and vertical shading components, and the first and second correction data forming means. The first storage means for storing the shading correction data of No. 2 and the first storage means. The first shading correction data is added to the third shading correction data newly formed by the first correction data forming means to form fifth shading correction data, which is stored in the first storage means. Second shading correction data forming means for forming sixth shading correction data by adding the second shading correction data and the fourth shading correction data newly formed by the first correction data forming means. A second storage unit for storing the fifth and sixth shading correction data, and the shading correction data read from the second storage unit for storing the fifth and sixth shading correction data at the time of shooting. A subtractor for subtracting a corresponding shading correction signal from the output signal of the image sensor, To solve the above problems by being adapted to supply to the subsequent signal processing circuit output signal of Ijitaru converter as an imaging output signal of the black shading-corrected.

Here, with no light incident on the image pickup surface of the image pickup device, the level data of the image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter and the level data A shading amount detecting means for detecting the shading amount by integrating the absolute value of the difference between the average levels is provided, and the effect of shading correction is confirmed.

A shading correction circuit according to the present invention is a shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device in which a plurality of pixels are arranged in a matrix, and the image pickup output signal of the image pickup device is An analog / digital converter for digitizing
The level data of the image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter is integrated in the horizontal direction and the vertical direction in a state where light having a uniform amount of light is incident on the entire image pickup surface of the image pickup device. And a first correction data forming means for forming first and second shading correction data corresponding to the horizontal and vertical shading components, and a first storage for storing the first and second shading correction data. Storage means, the first shading correction data stored in the first storage means, and the third shading correction data newly formed by the first correction data forming means are added to obtain a fifth shading correction data. Shading correction data of the first shading correction data is formed, and the second shading correction data stored in the first storage means is newly added to the first shading correction data. Second correction data forming means for adding the fourth shading correction data formed by the data forming means to form sixth shading correction data, and the fifth and sixth shading correction data are stored. The output signal of the image sensor is divided by a second storage unit and a shading correction signal corresponding to the shading correction data read from the second storage unit that stores the fifth and sixth shading correction data at the time of shooting. The above-described problem is solved by including a divider and supplying the output signal of the analog / digital converter to the signal processing circuit in the subsequent stage as an image pickup output signal subjected to white shading correction processing.

Here, the level data of the image pickup output signal of each pixel of the image pickup device, which is digitized by the analog / digital converter, in a state where light having a uniform light amount is incident on the entire image pickup surface of the image pickup device, The shading amount detecting means for detecting the shading amount by integrating the absolute value of the difference between the average levels of the level data is provided, and the effect of the shading correction is confirmed.

[0015]

In the present invention, the image pickup output signal of the image pickup device in which a plurality of pixels are arranged in a matrix is digitized by the analog / digital converter in a state where no light is incident on the image pickup surface of the image pickup device. Level data of the image pickup output signal of a predetermined number of pixels is stored in the first storage unit as black shading correction data, and the black shading correction signal is read based on the black shading correction data read from the first storage unit at the time of actual image pickup. To correct the black shading of the image pickup output signal of the image pickup element, quickly and appropriately and automatically. Further, the correction amount of black shading correction with respect to the detection amount of black shading is freely set.

Further, an image pickup output signal of an image pickup device in which a plurality of pixels are arranged in a matrix is digitized by an analog / digital converter in a state where light having a uniform light quantity is incident on the entire image pickup surface of the image pickup device. Level data of the image pickup output signals of the predetermined number of pixels are stored in the first storage unit as white shading correction data, and white shading is performed based on the white shading correction data read from the first storage unit during actual image pickup. A correction signal is formed, and white shading correction processing of the image pickup output signal of the image pickup device is automatically performed quickly and appropriately. Further, the correction amount of white shading correction with respect to the detected amount of white shading is freely set.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the shading correction circuit according to the present invention will be described in detail below with reference to the drawings.

In the embodiment shown in FIG. 1, the present invention is applied to a three-plate type color image pickup device, and image pickup outputs of RGB channels obtained by the first, second and third image pickup elements 1R, 1G and 1B. The signals E _R , E _G , E _{B comprise} a correction processing circuit 3 which is supplied via preamplifiers 2R, 2G, 2B, respectively.

In this embodiment, the image pickup device 1R,
Reference numerals 1G and 1B form an image pickup section of the three-plate color image pickup apparatus, and are provided in an image pickup optical system 7 including an image pickup lens 4, an iris mechanism 5, a color separation prism 6 and the like. As shown in FIGS. 2, 3 and 4, the image pickup devices 1R, 1G, and 1B have M * N pixels S _{11 to} S _MN in the horizontal direction and N pixels in the vertical direction in a matrix. The CCD image sensors arranged in a pattern are driven by a CCD driving unit (not shown) so that the signal charges of all pixels S _{11 to} S _MN for one screen are read in one vertical scanning period.

Then, the first image pickup device 1R uses the image pickup output signal E _R of the red component of the subject image color-separated by the color separation prism 6 as an R channel signal to perform the correction via the preamplifier 2R. It is supplied to the processing circuit 3.
The second image pickup device 1G uses the image pickup output signal E _G of the green component of the subject image color-separated by the color separation prism 6 as a G channel signal via the preamplifier 2G to correct the correction processing circuit 3G. Supply to. Further, the second image pickup device 1B uses the image pickup output signal E _B of the blue component of the subject image color-separated by the color separation prism 6 as a B channel signal via the preamplifier 2B to correct the correction processing circuit 3 Supply to.

The correction processing circuit 3 performs black shading correction processing and white shading correction processing on the image pickup output signals E _R , E _G , and E _B of RGB channels obtained by the image pickup devices 1R, 1G, and 1B. And the subtractors 8R, 8G, 8B for the respective RGB channels to which the image pickup output signals E _R , E _G , E _B are supplied.
And the subtraction output signals from the subtractors 8R, 8G, and 8B are supplied via the variable gain amplifiers 9R, 9G, and 9B to the dividers 10R and 10R for the respective RGB channels.
G and 10B.

In the correction processing circuit 3, the subtractors 8R, 8G, and 8B perform black shading correction processing on the image pickup output signals E _R , E _G , and E _B of the RGB channels, respectively. Signal forming unit 14
The RGB shading correction signals B _RSH , B _GSH , and B _BSH of the respective RGB channels supplied from
Black shading correction processing is performed by subtracting from _R , E _G , and E _B. In addition, each variable gain amplifier 9 described above
R, 9G, and 9B are for performing signal level adjustment such as white balance adjustment and black balance adjustment for the image pickup output signals E _R , E _G , and E _B of the RGB channels, and RGB supplied from the system controller 27 described later.
Each gain is controlled by the control signal of each channel. Furthermore, each of the dividers 10R, 10G, and 10B has RGB
White shading correction signals W _RSH , W _{GSH of} RGB channels supplied from a shading correction signal forming unit 14 to be described later are provided for performing white shading correction processing on the imaging output signals E _R , E _G , E _B of each channel. W
White shading correction processing is performed by dividing the image pickup output signals E _R , E _G , and E _B by _BSH .

The above dividers 10R, 10G, 10B
The white shading correction signal W _RSH, W_GSH, W
_BSHThe reciprocal of is the imaging output signal E of each RGB channel_R,
E_G, E_BIt is okay to use a multiplier that multiplies
Yes.

The image pickup output signals E _R , E _G , and E _{B which} have been subjected to the correction processing by the correction processing circuit 3 are output from the correction processing circuit 3 to the prinny circuits 11R and 1R, respectively.
It is supplied to the A / D converters 12R, 12G, and 12B of RGB channels via 1G and 11B. Here, the purine circuits 11R, 11G, and 11B output the RGB signals output from the correction processing circuit 3 so that the input signal levels of the A / D converters 12R, 12G, and 12B do not exceed the dynamic range. Non-linear processing is performed on the imaging output signals E _R , E _G , and E _B of each channel.

Further, the A / D converters 12R, 12
G and 12B form level data indicating signal levels of the respective image pickup output signals E _R , E _G , and E _B that have been subjected to the correction processing by the correction processing circuit 3. A above
RG obtained by the A / D converters 12R, 12G, 12B
The level data of the image pickup output signals E _R , E _G , and E _B of the respective B channels are the same as the image pickup output simultaneous data D _R , D _G , and D _{B which have} been subjected to the shading correction processing, and the defect correction processing circuits 13R, 13G, and 13B are used. The signal is supplied to the shading correction signal forming unit 14 and a signal processing circuit in the subsequent stage (not shown) via the via.

The defect correction processing circuits 13R and 13R
G and 13B perform defect correction processing so as to correct the signal levels of the signal charges due to the defective pixels of the image pickup devices 1R, 1G and 1B, that is, the image pickup output signals E _R , E _G and E _B of the RGB channels. Therefore, the defect correction processing is performed based on the level data of the defective pixels detected in advance for the image pickup devices 1R, 1G, and 1B.

Further, the shading correction signal forming section 14 is a low-pass filter 15 to which the image pickup output simultaneous data D _R , D _G , D _{B of the} RGB channels are supplied.
R, 15G, 15B, these low-pass filters 15R,
The image pickup output simultaneous data D _R via 15G and 15B,
The data selector 16 to which D _G and D _B are supplied, and the dot sequential data D [R /
G / B] is supplied to the data processing circuit 17, a rewritable random access memory (RAM: Random Access Memory) connected to the data processing circuit 17, the detection working memory 18, the correction working memory 26, And electrically erasable read-only memory (EEPROM: Electrically Erasable and Programmable
The read-only memory backup memory 19 and the black shading correction data D [ _BRSH / _BGSH / _BBSH ] output dot-sequentially from the data processing circuit 17 are stored in R
The data selector 20 which distributes to each channel of GB, and the white shading correction data D [W _RSH / W _GSH / W _BSH ] output from the data processing circuit 17 in a dot-sequential manner are RG.
B data selector 21 for distributing to each channel B, black shading correction data D [ _BRSH ], D [B for each channel of RGB distributed by the data selector 20.
_GSH ] and D [ _BBSH ] are _converted to analog D /
White shading correction data D [W _RSH ], D [W _GSH ], D [W of RGB channels distributed by the A converters 22R, 22G, 22B and the data selector 21.
_BSH ] to each D / A converter 23
R, 23G, 23B, these D / A converters 22R, 22
Low pass filters 24R, 24G, 24B, 25R provided on the output side of G, 22B, 23R, 23G, 23B,
It is composed of 25G and 25B.

In the shading correction signal forming section 14, the low pass filters 15R, 15G and 15B are provided.
Are the A / D converters 12R, 12G, 12B, respectively.
Is a digital filter having a cutoff frequency of ⅛ of the clock frequency of the above, and performs band limiting processing for limiting the band of the image pickup output simultaneous data D _R , D _G , D _B to ⅛.

Further, the data selector 16 outputs the image pickup output simultaneous data D _R , D _G , D _B of each of the R, G, B channels which are band-limited by the low pass filters 15R, 15G, 15B as one channel. Point-sequential data D, which is selected point by point, and the number of data is thinned to 1/4
[R / G / B] is formed. The dot-sequential data D [R / G / B] formed by the data selector 16 is indicated by hatching in FIG. 2, FIG. 3 and FIG.
The signal level of the image pickup output signal by the signal charges of all the pixels S _{11 to} S _MN of R, 1G, and 1B is shown in a dot-sequential manner.

Here, the image pickup devices 1R, 1G, 1B
The drive unit 28 of the iris mechanism 5 of the image pickup optical system 7 is controlled by the system controller 27, and when detecting the black shading characteristic, the iris mechanism 5 is closed and light is incident on each image pickup surface. In the case where the image pickup operation is performed in the state of not being performed and the white shading characteristic is detected, the iris mechanism 5 is opened and, for example, a white pattern such as a porta pattern is used, and the luminance is equal to 100% on the entire image pickup surface. Imaging is performed in a state where light with a uniform light amount is incident.

Then, the data processing circuit 17 is
Black shading characteristics of the image pickup devices 1R, 1G, 1B and
Black shading correction data according to white shading characteristics.
Data D [B_RSH/ B_GSH/ B_BSH] And White Shadin
Correction data D [W_RSH/ W _GSH/ W_BSH] The above day
Dot sequential data D [R / G supplied from the data selector 16
/ B] and, as shown in A of FIG.
After storing in the working memory 18 for detection, as shown in FIG.
As shown, the correction working memory 26 is dot-sequentially
Remember. Furthermore, the data processing circuit 17 is actually
At the time of imaging of
Black shading correction data D [B_RSH/ B_GSH/ B
_BSH] And white shading correction data D [W_RSH/ W
_GSH/ W_{BS H}] Is read out in a dot-sequential manner, and each of the above selectors is read.
Output via 20 and 21.

In this embodiment, the data processing circuit 17 includes all the pixels S _{11 of the} image pickup devices 1R, 1G and 1B.
~ S _MN, the dot-sequential data D [R / G / B] indicating the signal level of the image pickup output signal by the signal charge for every four pixels is displayed in the horizontal direction as shown in FIGS. 2, 3 and 4. By integrating the level data indicating the imaging output levels of the pixels at the same positions P _{h1 to} P _hm , the data string D [l _h1 ~ l _hm ], and obtains this data string D
Horizontal shading correction data is formed dot-sequentially from [l _{h1 to} l _hm ], and at the same position P _{v1 in the} vertical direction.
By integrating the level data indicating an imaging output level of the pixel in the to P _vm, obtain a data string D [l _v1 to l _vm] indicating the vertical shading characteristics using the level data with improved S / N This data string D [l _v1 ~
shading correction data in the vertical direction is formed in a dot-sequential manner from l _vm ].

Such a data processing circuit 17 is constructed as shown in FIG. 6, for example. That is, in the data processing circuit 17 shown in FIG. 6, the dot sequential data D [R / G / B] from the data selector 16 is supplied to the clipping circuit 31. The clip circuit 31 operates the image pickup devices 1R and 1R for the dot sequential data D [R / G / B].
After subtracting the average value for each of the G and 1B screens in a dot-sequential manner,
The process of clipping to the lower n bits is performed, and the clipped dot-sequential data D [R / G / B] is supplied to the down-sampling circuit 32. The down-sampling circuit 32 uses the dot-sequential data D [R /
G / B], the dot-sequential data D [R / G / which indicates the shading characteristics of the image pickup devices 1R, 1G, and 1B is obtained by a digital filter having a transfer function H (z) as shown in equation (1). B] is limited to 1/16.

H (z) = 1/4 × z ^-4 + 1/2 × z ⁰ + 1/4 × z ⁴ (1)

Point-sequential data D [R / G /, which has been down-sampled by the down-sampling circuit 32.
B] is supplied to the accumulator 33 and the absolute value conversion circuit 46. The absolute value conversion circuit 46 removes the sign of the dot-sequential data D [R / G / B] that has been down-sampled by the down-sampling circuit 32, converts it to absolute value data, and supplies it to the integration circuit 47. The integration circuit 47 synchronously adds the dot-sequential data D [R / G / B] converted into absolute values by the absolute value conversion circuit 46 for each RGB channel by synchronous addition of the level data of each RGB channel. The above system controller 2
Output to 7.

On the other hand, the accumulator 33 is
For the sequential data D [R / G / B], the detection data
King memory 18 is used and shown in FIG. 2, FIG. 3 and FIG.
, The same position P in the horizontal direction_h1~ P_hmOf pixels in
Simultaneously add and integrate level data indicating the image output level
As a result, the horizontal direction of each image sensor 1R, 1G, 1B
Black shading as shading correction data
Correction data D [B_RSH/ B_GSH/ B_BSH]_HOr white
Trading correction data D [W_RSH/ W_GSH/ W _BSH]_H
Are formed in a dot-sequential manner and the same position in the vertical direction.
Setting P_v1~ P_vmLevel indicating the image output level of the pixel in
By integrating the data, each image sensor 1R, 1G,
Black as vertical shading correction data for each 1B
Shading correction data D [B_RSH/ B_GSH/
B_BSH]_VOr white shading correction data D [W_RSH
/ W_GSH/ W_BSH]_VAre formed dot-sequentially.

Here, the horizontal black shading is performed.
Correction data D [B_RSH/ B_GSH/ B _BSH]_HOr white
Trading correction data D [W_RSH/ W_GSH/ W_BSH]_H
Using the working memory 18 for detection,
Formed by the synchronous addition above, and also in the vertical direction above
Black shading correction data D [B_RSH/ B_GSH/ B
_BSH]_VOr white shading correction data D [W_RSH/
W_GSH/ W_BSH]_VIs due to the synchronous addition on the register
It is formed.

In this way, the dot sequential data D [R /
G / B], the image pickup elements 1R, 1G, 1B
Horizontal black shading correction data D [ _BRSH /
B _{GS H} / B _{BSH] H} and vertical black shading correction data D [B _RSH / B _GSH / B _{BSH] V,} or horizontal white shading correction data D [W _RSH / W _{GS H}
/ W _BSH ] _H and vertical white shading correction data D [W _RSH / W _GSH / W _BSH ] _V are written and stored dot-sequentially in the detection working memory 18, respectively.

Horizontal black shading correction data D [ _BRSH stored in the detection working memory 18].
/ _BGSH / _BBSH ] _H and vertical black shading correction data D [ _BRSH / _BGSH / _BBSH ] _V or horizontal white shading correction data D [ _WRSH / W]
_GSH / W _BSH ] _H and vertical white shading correction data D [W _RSH / W _GSH / W _BSH ] _V are stored in buffer 3
4 is supplied to the multiplier 43.

The multiplier 43 converts the coefficient signal K supplied from the system controller 27 into horizontal black shading correction data D [ _BRSH / _BGSH / _BBSH ] _H.
And vertical black shading correction data D [ _BRSH
/ B _GSH / B _BSH ] _V or horizontal white shading correction data D [W _RSH / W _GSH / W _BSH ] _H and vertical white shading correction data D [W _RSH / W
_GSH / W _BSH ] _V is multiplied. Then, the multiplier 43
Horizontal black shading correction data D [ _BRSH / _BGSH / _BBSH ] _H and vertical black shading correction data D [ _BRSH / _BGSH / B
_BSH ] _V or horizontal white shading correction data D [ _WRSH / _WGSH / _WBSH ] _H and vertical white shading correction data D [ _WRSH / _WGSH / _WBSH ]
_V is supplied to the adder 44.

In the adder 44, the multiplier 43
The horizontal black shading correction data
Data D [B_RSH/ B_GSH/ B_BSH]_HAnd vertical black
Shading correction data D [B_RSH/ B_GSH/
B_BSH]_V, Or the horizontal white shading correction
Data D [W_RSH/ W_GSH/ W_BSH]_HAnd vertical white
Shading correction data D [W_RSH/ W_GSH/
W_BSH]_VAnd stored in the working memory for correction 26
Horizontal black shading correction data D
[B_{RS H}/ B_GSH/ B_BSH]_HAnd vertical black shade
Ding correction data D [B_RSH/ B_GSH/ B_BSH]
_VAnd horizontal white shading correction data D [W
_RSH/ W_GSH/ W_BSH]_HAnd vertical white shade
Correction data D [W_RSH/ W _GSH/ W_BSH]_VAnd
Add each. Then, the adder 44 adds
The horizontal black shading correction data D [B
_RSH/ B_GSH/ B_BSH] _HAnd vertical black shady
Correction data D [B_RSH/ B_GSH/ B_BSH]_VAnd water
Horizontal white shading correction data D [W_RSH/ W
_GSH/ W_BSH]_HAnd vertical white shading correction
Data D [W_RSH/ W_GSH/ W_BSH]_VAnd the above correction
Is written and stored in the working memory 26.

Further, horizontal black shading correction data D stored in the correction working memory 26.
[ _BRSH / _BGSH / _BBSH ] _H and vertical black shading correction data D [ _BRSH / _BGSH / _BBSH ]
_V and horizontal white shading correction data D [W
_RSH / _WGSH / _WBSH ] _H and vertical white shading correction data D [ _WRSH / _WGSH / _WBSH ] _V
When the shading correction processing is applied to the image pickup output signals E _R , E _G , and E _B of each of the RGB channels, they are sequentially read out from the working memory 26 and supplied to the data separator 35 via the buffer 42.

The data separator 35 is arranged in the horizontal direction.
Black shading correction data D [B _RSH/ B_GSH/ B
_BSH]_HAnd white shading correction data D [W_RSH/
W_GSH/ W_BSH]_HAnd vertical black shading
Positive data D [B_RSH/ B_GSH/ B_BSH]_VAnd white shade
Ding correction data D [W_RSH/ W_GSH/ W_BSH]_VWhen
The horizontal black shading correction data above.
Type D [B_RSH/ B_GSH/ B_BSH]_HAnd above horizontal white
Shading correction data D [W_RSH/ W_GSH/ WBSH
 ]_HAre supplied to the interpolation processing circuit 36, and
Direction black shading correction data D [B_RSH/ B_GSH
/ B_BSH]_VAnd the vertical white shading correction
Data D [W_RSH/ W_GSH/ W_BSH]_VAnd adder 3
7 and 38.

The interpolation processing circuit 36 uses the data separator.
Dot-sequential at the data rate of the clock frequency from the transmitter 35
Horizontal black shading correction data D supplied to
[B _RSH/ B_GSH/ B_BSH]_HAnd horizontal white shade
Ding correction data D [W_{RS H}/ W_GSH/ W_BSH]_HTo
Then, average value interpolation processing is applied to
Ding correction data D [B_RSH/ B_GSH/ B_BSH]_HWhen
The horizontal white shading correction data D [W_RSH
/ W_GSH/ W_BSH]_HTo separate the clock frequency
Output at 1/4 data rate. Interpolation processing circuit 3
Data rate of 1/4 of the clock frequency obtained by
Horizontal black shading correction data D [B_RSH
/ B_GSH/ B_BSH]_HIs supplied to the adder 37
It The adder 37 is provided with the horizontal black shading
Correction data D [B_RSH/ B_GSH/ B_BSH]_HAnd above
Direct black shading correction data D [B_RSH/ B
_GSH/ B_BSH]_VBy adding and,
And vertical black shading correction data D [B_RSH/
B_GSH/ B_BSH] Through the clip circuit 39
Output. In addition, obtained by the interpolation processing circuit 36
Data rate of 1/4 the clock frequency
White shading correction data D [W_RSH/ W_GSH/ W
_BSH]_HIs supplied to the adder 38. This adder
38 is the horizontal white shading correction data D
[W_RSH/ W_GSH/ W_BSH]_HAnd the vertical white shel
Trading correction data D [W_RSH/ W_GSH/ W_BSH]_V
Add and to add horizontal and vertical white shading
Correction data D [W_RSH/ W_GSH/ W _BSH] To form
Output through the clipping circuit 39.

[0045] The data processing circuit 17 black shading dot are sequentially outputted from the correction data D [B _RSH / B _GSH
/ B _BSH ], the selector 20 supplies the black shading correction data D [B _RSH / B _GSH / B _BSH ].
To the D / A converters 22R, 22
It is to be distributed and supplied to G and 22B, and is composed of, for example, a latch circuit. Then, the D / A converters 22R, 2
2G, 22B, said black shading correction data D supplied from the selector 20 [B _RSH / B _{GS H} / B
_BSH ] is _converted to analog.

The black shading correction data D [B
The output signal of the D / A converter 22R for analogizing _RSH ] is supplied as a black shading correction signal B _{RSH to} the R channel subtractor 8R of the correction processing circuit 3 via the low pass filter 24R. The output signal of the D / A converter 22G, which converts the black shading correction data D [B _GSH ] into an analog signal, is black-shaded to the G channel subtractor 8G of the correction processing circuit 3 via the low pass filter 24G. It is supplied as a correction signal B _{GS H.} Further, the D / A converter 22 for analogizing the black shading correction data D [ _BBSH ]
The B output signal is supplied to the B channel subtractor 8B of the correction processing circuit 3 as the black shading correction signal B _BSH via the low pass filter 24B.

Also, from the data processing circuit 17, dot-sequential
The white shading correction data D [W
_RSH/ W_GSH/ W_BSH] Is supplied to the selector 21
Is_,The white shading correction data D [W_RSH/ W
_GSH/ W_BSH]] D / A conversion of each of the RGB channels
It supplies and distributes to the vessels 23R, 23G and 23B.
For example, it is composed of a latch circuit. And the above D / A change
The converters 23R, 23G, and 23B are connected to the selector 21.
The white shading correction data D [W _RSH
/ W_GSH/ W_BSH] To each analog.

The white shading correction data D [W
The output signal of the D / A converter 23R for analogizing _RSH ] is supplied as a white shading correction signal W _{RSH to} the R-channel divider 10R of the correction processing circuit 3 via the low-pass filter 25R. The output signal of the D / A converter 23G, which converts the white shading correction data D [W _GSH ] into an analog signal, is white-shaded to the G-channel divider 10G of the correction processing circuit 3 via the low-pass filter 25G. Correction signal W _GSH
Supplied as. Further, the output signal of the D / A converter 23B for converting the white shading correction data D [ _WBSH ] into an analog signal is supplied to the B channel divider 10B of the correction processing circuit 3 via the low pass filter 25B.
_Is supplied as a white shading correction signal W _BSH .

The shading correction circuit of this embodiment is
The system controller 27 controls as shown in the flowchart of FIG. When the shading correction mode is set, first, a black shading characteristic detecting operation is started. In step S1, the iris mechanism 6 is detected.
To close. Thereby, the image pickup devices 1R, 1G,
1B performs an imaging operation in a state where no light is incident on each imaging surface.

In the next step S2, the shading amount is detected. This is the integration result of the absolute values of the level data of the RGB channels output from the integration circuit 47, and increases in proportion to the shading amount. Therefore, the shading amount can be detected by detecting the integration result.

In the next step S3, the shading amount detected in step S2 is compared with the standard value. If the shading amount is below the standard, the process proceeds to step S5, and if the shading amount exceeds the standard. , And proceeds to step S4. This determination is performed in order to determine whether or not the contents of the black shading correction data D [ _BRSH / _BGSH / _BBSH ] currently stored in the correction working memory 26 are appropriate.

In step S4, after the black shading correction data D [ _BRSH / _BGSH / _BBSH ] stored in the correction working memory 26 is preset,
Black shading characteristics are detected. When this detection is performed, the black shading correction data D [ _BRSH / _BGSH / _BBSH ] according to the black shading characteristic is written in the detection working memory 18. Then, this black shading correction data D [ _BRSH / _BGSH / B
_BSH ] is written to the correction working memory 26 via the multiplier 43 and the adder 44. For example, the multiplier 43
To the adder 44 so that the black shading correction data D [ _BRSH / _BGSH / _BBSH ] stored in the correction working memory 26 is not input to the adder 44. Open the switch. That is, the black shading correction data D [ _BRSH / _BGSH / _BBSH ] written in the detection working memory 18 is stored in the correction working memory 26 without being calculated. .

In step S5, the shading amount is detected again. However, unlike the detection of the shading amount performed in step S2, the integration time constant for detecting the accurate shading amount is increased to, for example, 10 screens. This is the image pickup device 1R, 1G, 1B.
The time constant is set to eliminate the influence of the amount of random noise included in the image pickup output signals E _R , E _G , and E _B.

Next, in step S6, black shading characteristics are detected. When this detection is done,
The black shading correction data D [ _BRSH / _BGSH / _BBSH ] corresponding to the black shading characteristic is written in the detection working memory 18. Then, this black shading correction data D [ _BRSH / _BGSH / _BBSH ]
Are written in the correction working memory 26 via the multiplier 43 and the adder 44. Also, the multiplier 43 supplies a coefficient K 1 below, for example, 0.5, the black shading to the adder 44 is stored in the correction working memory 26 the correction data D [B _RSH / B _GSH /
B _BSH ] is input, the switch of the adder 44 is closed. That is, in the correction working memory 26, the black shading correction data D [ _BRSH / _BGSH / _BBSH ] previously stored and the black written in the detection working memory 18 multiplied by the coefficient K are written. Black shading correction data D [B _RSH / B _GSH added with shading correction data D [B _RSH / B _GSH / B _BSH ]
/ _BBSH ] is written. This makes it possible to effectively utilize the result of previously detecting the black shading characteristic. Also, by making the value of the coefficient K variable,
Since the adjustment sensitivity can be changed, fine adjustment can be performed. Furthermore, since there is an integration effect, it is possible to suppress the influence of the amount of random noise included in the image pickup output signals E _R , E _G , and E _B.

Next, in step S7, the shading amount is detected three times. The processing operation of detecting the shading amount is exactly the same as the processing operation performed in step S5.

After this, in step S8, it is determined whether or not the black shading detection operation is to be ended. In this determination, if the shading amount detected in step S7 is below the standard, the process proceeds to step S9, and if the shading amount exceeds the standard, the process returns to step S6.

However, if the shading amount cannot be accurately detected due to the influence of the random noise amount contained in the image pickup output signals E _R , E _G , and E _B , the shading amount detected in step S7, When the shading amount detected in the previous step is compared, and the shading amount detected in step S7 becomes larger than the shading amount detected before that, the process proceeds to step S9, and when it becomes smaller. To return to step S6. In other words, when the shading amount is reduced by the detection of the black shading characteristic in step S6, the detection is performed again, and when the shading amount is increased, that is, when only the influence of random noise is detected, the black shading characteristic It is intended to end the detection operation.

Further, in step S9, it is determined whether or not the white shading characteristic detecting operation is to be continued. When the white shading characteristic detection operation is not performed by this determination, the control operation of the shading characteristic detection mode ends, but when the white shading characteristic detection operation is performed, the process proceeds to step S10.

In step S10, the iris mechanism 6 is opened. Then, the image pickup devices 1R, 1G, 1B
Uses a white pattern such as a porta pattern,
Imaging is performed in a state where a uniform amount of light having a brightness of 100% is incident on the entire imaging surface.

Then, in the next step S11, the shading amount is detected. This is the integration result of the absolute titanium nitride film of the level data of the RGB channels output from the integration circuit 47 and increases in proportion to the shading amount. Therefore, the shading amount can be detected by detecting the integration result.

In the next step S12, step S11
Compare the shading amount detected in and the standard value,
If the shading amount is below the standard, step S1
If the shading amount exceeds the standard, go to step S13. This determination is performed to determine whether or not the contents of the white shading correction data D [W _RSH / W _GSH / W _BSH ] currently stored in the correction working memory 26 are appropriate.

At step S13, the correction work-in-process is performed.
White shading correction data stored in memory 26.
Data D [W_RSH/ W_GSH/ W_BSH] Was preset
After that, the white shading characteristic is detected. This detection
Is performed, the white shading according to the white shading characteristics is performed.
Ding correction data D [W_RSH/ W_GSH/ W_BSH] Is above
It is written in the working memory 18 for detection. That
The white shading correction data D [W_RSH/ W
_GSH/ W_BSH] Through the multiplier 43 and the adder 44
The correction working memory 26 is written. This station
In step S13, the coefficient K supplied to the multiplier 43 is set to 1
In the adder 44, the correction working memory 26
Stored white shading correction data D [W_RSH
/ W_GSH/ W_{BS H}]] Is not input to the adder 44
Open the switch. That is, the working memory for detection
White shading correction data D [W
_RSH/ W _GSH/ W_BSH] Is not calculated
In addition, to store in the correction working memory 26
Become.

In step S14, the shading amount is detected again. However, unlike the detection of the shading amount performed in step S11, the integration time constant for detecting the accurate shading amount is increased to, for example, 10 screens. This is the image pickup device 1R, 1G,
The time constant is set so that the influence of the amount of random noise included in the image pickup output signals E _R , E _G , and E _B from 1B is eliminated.

Next, in step S15, the white shade
The ding characteristic is detected. This detection is done
And white shading compensation according to the white shading characteristics.
Positive data D [W_RSH/ W_GSH/ W_BSH] For the above detection
It is written in the working memory 18. And this white
Shading correction data D [W_RSH/ W_GSH/
W_BSH] Through the multiplier 43 and the adder 44
The working memory 26 is written. Also the above multiplication
The coefficient K supplied to the container 43 is set to 1 or less, for example 0.5
In the adder 44, the correction working memory 26
Stored white shading correction data D [W_RSH
/ W_GSH/ W_BSH] Is input to the adder 44
Close the switch. That is, the working memo for correction
Re26 contains the previously stored white shading supplement.
Positive data D [W_RSH/ W_GSH/ W_BSH] And the coefficient K
White written in the working memory 18 for detection
Shading correction data D [W_RSH/ W_GSH/
W_BSH] And white shading correction data D
[W_RSH/ W_GSH/ W_BSH] Is written. By this
The result of previous detection of white shading characteristics
Can be effectively utilized. In addition, the value of coefficient K
You can change the adjustment sensitivity by making it variable.
Then, it becomes possible to make fine adjustments. Furthermore, the integral effect
Therefore, the image pickup output signal E_R, E _G, E_Binclude
The influence of the amount of random noise can be suppressed.

Next, in step S16, the shading amount is detected three times. The processing operation of detecting the shading amount is exactly the same as the processing operation performed in step S14.

Thereafter, in step S17, it is determined whether or not the white shading detection operation is to be ended. In this determination, if the shading amount detected in step S16 is less than or equal to the standard, the process proceeds to step S18,
If the shading amount exceeds the standard, step S
Return to 15.

However, if the shading amount cannot be accurately detected due to the influence of the random noise amount contained in the image pickup output signals E _R , E _G , and E _B , the shading amount detected in step S16, If the shading amount detected in step S16 is compared with the shading amount detected in the previous step and the shading amount detected in step S16 is greater than the shading amount detected in the previous step, the process proceeds to step S18 To return to step S15. In other words, when the shading amount decreases due to the white shading characteristic detection in step S15, the white shading characteristic is detected again, and when the shading amount increases, that is, when only the influence of random noise is detected, the white shading characteristic It is intended to end the detection operation.

Then, in step S18, the white balance adjustment processing is performed, and then the control operation of the shading characteristic detection mode is terminated. In this step S18, RG obtained by the image pickup devices 1R, 1G, 1B
Imaging output signal B each channel E _R, E _G, with E _B, this way the black shading taken sequentially point two said correcting working memory 26 the correction data D
Black shading correction processing based on [ _BRSH / _BGSH / _BBSH ] and white shading correction data D [ _WRSH /
W _GSH / W _BSH ], the correction processing circuit 3 is configured so that the image pickup output simultaneous data D _R , D _G , and D _B of the respective channels have the same signal level in a state where the white shading correction processing is performed. Variable gain amplifier 9R, 9
White balance adjustment is performed by setting gains of G and 9B.

Here, the black shading characteristic and the white shading characteristic may be influenced by the usage condition and environment, but they are not much deteriorated without frequent correction. Therefore, if the latest black shading correction data and white shading correction data obtained by the shading characteristic detection operation are stored in the backup memory 19 by the EEPROM, the correction data remains, and thus the shading characteristic has a problem in use. It is not necessary to perform the detection operation except in the case.

[0070]

As is apparent from the above description, the shading correction circuit according to the present invention is a shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device in which a plurality of pixels are arranged in a matrix. And an analog / digital converter for digitizing the image pickup output signal of the image pickup device, and the image pickup device digitized by the analog / digital converter in a state where no light is incident on the image pickup surface of the image pickup device. First correction data forming means for integrating the level data of the image pickup output signal of the pixel in the horizontal direction and the vertical direction to form first and second shading correction data corresponding to the shading components in the horizontal direction and the vertical direction. A first storage means for storing the first and second shading correction data,
The first shading correction data stored in the first storage means and the third shading correction data newly formed by the first correction data forming means are added to obtain fifth shading correction data. Sixth shading is performed by adding the second shading correction data which has been formed and is stored in the first storage means and the fourth shading correction data which is newly formed by the first correction data forming means. Second correction data forming means for forming correction data, second storage means for storing the fifth and sixth shading correction data, and fifth storage means for storing the fifth and sixth shading correction data at the time of shooting. Two
A subtractor for subtracting a shading correction signal corresponding to the shading correction data read from the storage means from the output signal of the image sensor,
The output signal of the digital converter is supplied to the signal processing circuit in the subsequent stage as an image pickup output signal which has been subjected to the black shading correction processing, so that the black shading correction processing can be performed automatically quickly and appropriately. .
Further, it is possible to effectively use the black shading correction data that has already undergone the correction processing. Further, the correction amount of the black shading correction with respect to the detection amount of the black shading can be freely set, so that the influence of random noise included in the image pickup output signal from the image pickup device can be suppressed.

Further, with no light incident on the image pickup surface of the image pickup device, the level data of the image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter and the average of the level data are obtained. The shading amount detecting means for detecting the shading amount by integrating the absolute value of the level difference is provided, and by confirming the effect of the shading correction, the random noise and the black shading amount included in the image pickup output signal of the image pickup device are detected. It can be detected separately.

The shading correction circuit according to the present invention is a shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device in which a plurality of pixels are arranged in a matrix. An analog / digital converter for digitizing
The level data of the image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter is integrated in the horizontal direction and the vertical direction in a state where light having a uniform amount of light is incident on the entire image pickup surface of the image pickup device. And a first correction data forming means for forming first and second shading correction data corresponding to the horizontal and vertical shading components, and a first storage for storing the first and second shading correction data. Storage means, the first shading correction data stored in the first storage means, and the third shading correction data newly formed by the first correction data forming means are added to obtain a fifth shading correction data. Shading correction data of the first shading correction data is formed, and the second shading correction data stored in the first storage means is newly added to the first shading correction data. Second correction data forming means for adding the fourth shading correction data formed by the data forming means to form sixth shading correction data, and the fifth and sixth shading correction data are stored. The output signal of the image sensor is divided by a second storage unit and a shading correction signal corresponding to the shading correction data read from the second storage unit that stores the fifth and sixth shading correction data at the time of shooting. A divider is provided, and the output signal of the analog / digital converter is supplied to the signal processing circuit in the subsequent stage as an image pickup output signal that has been subjected to white shading correction processing, so that white shading correction processing can be performed quickly and appropriately. Can be applied automatically. Further, it is possible to effectively use the white shading correction data that has already undergone the correction processing. Further, the correction amount of white shading correction with respect to the detection amount of white shading can be freely set, so that the influence of random noise included in the image pickup output signal from the image pickup device can be suppressed.

Further, level light of the image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter in a state where light having a uniform light amount is incident on the entire image pickup surface of the image pickup device, The shading amount detection means for detecting the shading amount by integrating the absolute value of the difference between the average levels of the level data is provided, and by confirming the effect of the shading correction, the random noise included in the image pickup output signal of the image pickup device is detected. The white shading amount can be detected separately.

In addition, the level data of the image pickup output signal of each pixel of the image pickup device which is digitized by the analog / digital converter is integrated in the vertical direction and the horizontal direction, and is integrated according to the shading components in the horizontal direction and the vertical direction. Since the first and second shading correction data are formed, the data amount of the shading correction data used for the shading correction can be reduced, and the first and second shading can be performed by using the storage unit having a small storage capacity. Correction data can be stored.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a shading correction circuit according to the present invention.

FIG. 2 is a diagram showing an arrangement state of pixels by the image sensor 1R and shading characteristics in horizontal and vertical directions thereof.

FIG. 3 is a diagram showing an arrangement state of pixels by the image sensor 1G and shading characteristics in horizontal and vertical directions thereof.

FIG. 4 is a diagram showing an arrangement state of pixels by the image pickup device 1B and shading characteristics in horizontal and vertical directions thereof.

FIG. 5 is a diagram showing a data string of black shading correction data and white shading correction data stored in a memory.

FIG. 6 is a block diagram showing a specific configuration of a data processing circuit of a shading correction signal forming unit.

FIG. 7 is a flowchart showing control contents by the system controller 27 of FIG.

[Explanation of symbols]

1R, 1G, 1B: Image sensor 3: Correction processing circuit 4: Imaging lens 5:・ ・ ・ Iris mechanism 6 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Color separation prism 7 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Imaging optical system 8R, 8G, 8B ・ ・ ・ ・ ・Subtractors 9R, 9G, 9B ... Divider 14 ... Shading correction signal forming unit 17 ... Data processing circuit 18 ...・ ・ ・ ・ ・ ・ ・ ・ Working memory for detection 19 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Backup memory 26 ・ ・ ・ ・ ・ ・ ・ ・ Working memory for correction 27 ・ ・ ・ ・ ・ ・.... System controller

Continuation of the front page (56) Reference JP-A-3-262282 (JP, A) JP-A-4-330872 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 5 / 243 H04N 5/16 H04N 5/335

Claims (4)

(57) [Claims] 1. A shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device in which a plurality of pixels are arranged in a matrix, the analog / digital converter digitizing the image pickup output signal of the image pickup device. And the level data of the image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter in a state where no light is incident on the image pickup surface of the image pickup device is integrated in the horizontal and vertical directions. First correction data forming means for forming first and second shading correction data according to horizontal and vertical shading components, and first storage means for storing the first and second shading correction data. And the first shading correction data stored in the first storage means and the first supplementary shading correction data. The third shading correction data formed by the data forming means is added to form fifth shading correction data, and the second shading correction data stored in the first storage means and the new shading correction data are newly added. The second shading correction data forming means for adding the fourth shading correction data formed by the first shading correction data forming means to form the sixth shading correction data; and the fifth and sixth shading correction data. From the output signal of the image pickup device, a second storage unit that stores the shading correction signal corresponding to the shading correction data read from the second storage unit that stores the fifth and sixth shading correction data during shooting. And a subtractor for subtracting the output signal of the analog / digital converter. A shading correction circuit which is adapted to be supplied to a signal processing circuit at a subsequent stage as a processed image pickup output signal. 2. Level data of an image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter and an average of the level data in a state where no light is incident on the image pickup surface of the image pickup device. The shading correction circuit according to claim 1, further comprising shading amount detection means for detecting an amount of shading by integrating an absolute value of a level difference, and confirming an effect of shading correction. 3. A shading correction circuit for removing a shading component of an image pickup output signal of an image pickup device in which a plurality of pixels are arranged in a matrix, the analog / digital converter digitizing the image pickup output signal of the image pickup device. And level data of the image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter in a state where light having a uniform light amount is incident on the entire image pickup surface of the image pickup device in the horizontal and vertical directions. A first correction data forming unit that integrates to form first and second shading correction data according to the horizontal and vertical shading components, and stores the first and second shading correction data. A first storage means, a first shading correction data stored in the first storage means, and a new shading correction data Second shading correction data stored in the first storage means by adding the third shading correction data formed by the first correction data forming means to form fifth shading correction data. And second correction data forming means for forming sixth shading correction data by adding the fourth shading correction data newly formed by the first correction data forming means, and the fifth and sixth <br of a second storage means for storing shading correction data, shading correction signal according to the shading correction data read from the second storage means for storing shading correction data of said fifth and sixth at the time of shooting /> and a divider for dividing an output signal of the image pickup device, white shell output signal of the analog / digital converter Shading correction circuit, characterized in that is adapted to supply to the subsequent signal processing circuit as an imaging output signal of the loading-corrected. 4. Level data of an image pickup output signal of each pixel of the image pickup device digitized by the analog / digital converter in a state where light having a uniform light amount is incident on the entire image pickup surface of the image pickup device, 4. The shading correction circuit according to claim 3, further comprising shading amount detection means for detecting the shading amount by integrating the absolute value of the difference between the average levels of the level data, and confirming the effect of the shading correction.