JPS643393B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shading correction device for a cathode ray tube that receives an image input signal and projects an image, and particularly a shading correction device for the entire system including the optical system of a camera that takes images on the cathode ray tube. The present invention relates to a device that performs the following steps.

Conventionally, many techniques have been developed for correcting shading in document scanning devices of facsimile image transmitters and television cameras. In addition, technologies related to shading correction for flying spot scanner tubes (hereinafter referred to as FSS tubes), which are mainly intended for broadcasting, have been announced, but all of these technologies are for the purpose of imaging and do not involve image reception. It was not intended. In contrast, the present invention uses an FSS tube for the purpose of image reception, and although the basic technical idea regarding shedding correction is common, the specific methods are different. In particular, in devices that create color film for printing by photographing images projected on a cathode ray tube, the resolution of the image on the cathode ray tube is significantly lower than that of color film, so in order to compensate for this even a little. It is necessary to perform precise shading correction over the entire screen.

In imaging devices that use the bright spot of a facsimile or FSS tube as a light source, shading is corrected using the signal obtained by scanning a standard white plate, etc., positioned at the edge of the document to be imaged. Although a method is known, this method cannot be used in the case of image reception since there is no document to be scanned. In addition, in a simple image capturing device that uses the bright spot of an FSS tube as a light source, a photoelectric conversion element is placed in a position that does not interfere with imaging, picks up the luminous flux from the bright spot, and uses the output obtained from this to pick up the luminous flux from the bright spot. Therefore, the brightness is controlled to be constant and the obtained image output is corrected. This method is
Since the photoelectric conversion element is located at a biased position with respect to the fluorescent surface, it has shading itself, and the shading of the optical system that picks up the video signal cannot be corrected, so it is incomplete. On the other hand, in a photographing device using an image pickup tube, a reference signal obtained by imaging a white plate or an R, G, B colored plate illuminated with uniform illuminance is recorded in a frame memory. 2. Description of the Related Art A method of correcting a video signal obtained by imaging a subject using data is known. This method can be similarly used when using the bright spot of the FSS tube as a light source. Using this method, it is possible to set correction values for each pixel separately, so it is possible to perform strict shading correction on the entire screen.
This is effective for cameras that produce irregular shading depending on the location of the screen, such as CCD cameras. However, frame memories are expensive, and especially in the case of high-quality images having a large number of scanning lines, a large capacity memory is required, so it is difficult to use them as is. Particularly when dealing with color images, since the shading is different for each color, the memory required is tripled, resulting in an enormous amount of memory. Furthermore, it is difficult to directly apply such a shading correction technique to shading correction of an image projected on a cathode ray tube due to the circuit configuration. Furthermore, when the image projected on the FSS tube is taken with a camera, the shading is also caused by the camera's optical system, so simply correcting the shading of the projected image will not correct the final result. The shading of the resulting image will not be completely corrected. Therefore, when photographing a projected image with a camera, it is necessary to perform comprehensive shading correction that includes not only the shading of the FSS tube but also the shading of the camera's optical system. Furthermore, since the shading differs depending on the three primary colors, it is necessary to be able to correct the shading of the three primary colors individually.

An object of the present invention is to provide a shading correction device capable of satisfactorily correcting the shading of an image projected on a cathode ray tube, and in particular to a shading correction device that can be used not only on a cathode ray tube but also on a camera when an image projected on a cathode ray tube is photographed with a camera. The object of the present invention is to provide a shading correction device that can comprehensively and accurately correct the shading of the three primary colors that occurs even in the optical system of the present invention, and that is inexpensive in construction.

The present invention divides a thruster image projected on a cathode ray tube using a standard signal into several ranges each including a plurality of pixels, and stores the representative value of the received light output within each division in a memory as a shading correction signal. The image input signal and a shading correction signal obtained by interpolating the correction signal stored in the memory are applied to a modulator to give the image input signal a characteristic opposite to the shading characteristic of the cathode ray tube. The present invention is characterized in that the image input signal thus modulated is applied to a brightness modulation terminal of a cathode ray tube to correct shading of the cathode ray tube.

Furthermore, the shading correction signal of the present invention is obtained by using an optical system having the same shading characteristics as the optical system of the camera to receive the raster image of the cathode ray tube, when an image projected on a cathode ray tube is photographed by a camera. The raster image on the cathode ray tube projected by the standard signal is divided into several ranges each including a plurality of pixels, and the representative value of the light reception output within the division is calculated as a shading correction signal. The image input signal and a shading correction signal obtained by interpolating the correction signal stored in the memory are applied to a modulator, and the image input signal is inversely matched to the shading characteristic of the cathode ray tube. modulated to give the characteristics of
The image input signal modulated in this manner is applied to a brightness modulation terminal of a cathode ray tube to correct shading of the cathode ray tube and the camera.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an embodiment of the shading correction device of the present invention. In this embodiment, the entire system is controlled by the system pulse generator 25 in synchronization with the image input signal.
H _S : Horizontal control signal for one screen, V _S : Vertical control signal for one screen, P: Flat pixel control signal, H _B : Horizontal control signal for block, V _B : Vertical control signal for block,
This is done by generating each signal and supplying them to the necessary circuits. First, when creating the shading correction data, set the changeover switch 21 to the white signal side and input the standard signal from the shading test signal generator 22 to the D/A converter 2.
0, the mirror 2 is moved to a position outside the optical path so that the light beam from the FSS tube 1 that displays a black and white image can travel straight. The light beam from the raster on the FSS tube 1 passes through a filter 6 and a shedding correction optical system 7 and enters a photomultiplier tube 8 . FSS tube deflection coil 2
7 receives horizontal and vertical control signals to control raster scanning from the system pulse generator 25.
Supply H _S and V _S. R, G, B filters 3 and 6
are made up of exactly the same thing. The correction optical system 7 including an aperture corrects the shading that occurs in the film 5 of the camera 4 and the photomultiplier tube 8 to be exactly the same. Shading correction is also performed at the same time. 1st
In the embodiment shown in the figure, the camera 4 and the photomultiplier tube 8 are installed in different locations, and the light beam from the FSS tube 1 is incident on either of them by the mirror 2. When manufacturing, it is also possible to replace the film and the photomultiplier tube in a dark box with one optical system.

R, G, B by switching the filter 6
The separately obtained outputs of the photomultiplier tubes 8 are supplied to an image signal processing circuit 9, where a scanning line is selected every four lines, and one
Pixel data is sampled and held every other pixel, A/D conversion is performed, and eight pieces of data are sequentially added and written into the buffer memory 10. Next, in the average value calculating circuit 11, the average value of the 16 data obtained and written for the 16 scanning lines extracted from each of the 64 scanning lines is calculated and used as the average value of one block. Therefore, the total number of pixels in one block is (2×8)×64=1024. In this example, as shown in Figure 2, the image on the FSS monitor is divided into 1568 blocks, 49 in the horizontal direction and 32 in the vertical direction, and the average value of each pixel in each block is calculated as the data of each block. It is said that The difference between the average values calculated for each block provides the shading. The shading caused by FSS tubes and optical systems is generally bright in the center, dark in the periphery, and the gradation in between changes gradually, so dividing it into 1568 blocks is enough to accurately detect the changes. can be expressed. The data of each block is stored in separate R, G, and B frame memories 12a, 12b, and 12c under the control of the memory control circuit 26, and is stored in the R, G, and B switcher 13 when correcting the input signal. Read out. Further, as shown in FIG. 1, the image signal processing circuit 9, buffer memory 10, average value calculation circuit 11, and memory control circuit 26 include:
Horizontal and vertical synchronization signals to control each circuit
In addition to H _S and V _S , a horizontal pixel signal P, horizontal and vertical block signals, H _B , V _B and other necessary signals are added. A microcomputer is used to calculate the average value because it requires low-speed calculation.

When adding an input signal to create a desired color film, set the changeover switch 21 on the input signal side and apply the input signal to the D/A converter 20.
B switchers 13, 19 and R, G, B filters 3,
6 is set at any position, the light beam from the FSS tube 1 is bent at right angles by the mirror 2, and a bright spot on the FSS tube is imaged on the film 5 of the camera 4 to take a photograph. The changeover switches 13, 19 and the filters 3, 6 are automatically switched one after another, and the R, G, B
The structure is such that each image is superimposed on the film. Input signal is interface 24
The control signals H _S , V _S ,
The data are sequentially read out via the D/A converter 20 under the control of P. In addition, the shading correction is
The correction data previously calculated using the reference signal and stored in the frame memories 12a, 12b, 12c is read out via the selection switch 13, and is sent to the modulators 17a, 17b, 17c together with the input signal.
This is done by adding to. When reading correction data from frame memories 12a, 12b, and 12c, if there is shading, input signals corresponding to adjacent blocks will be corrected by discontinuous correction data. Insertion is in progress. FIG. 3 is a diagram schematically showing a method of interpolation calculation. The data of each block is assumed to be the value at the center of each block, and the data of adjacent blocks are assumed to change linearly64.
It is divided into equal parts and the value on this equal dividing line is used as the interpolated value. In FIG. 3, if the data of adjacent blocks are V1 and V2, and the data on the nth equal dividing line counting from V1 is V, then V is expressed by the following equation.

V=V ₁ V ₂ −V ₁ /64×n (n=0 to 63) This calculation is performed 64 times for each block, a total of 100,352 times for the entire screen, so it takes too much time with a computer software program. The present invention uses logic circuits to perform high-speed calculations. FIG. 4 is a diagram showing a logic circuit for interpolation in the sub-scanning line direction used in one embodiment of the present invention. Data V ₁ and V ₂ of adjacent blocks in the sub-scanning direction (vertical scanning direction) are taken out from the frame memory to accumulators 31 and 32, and added to a subtracter 33 to calculate (V ₂ −V ₁ ). .
This result is added to the arithmetic unit 34, and the counted value n from the counter 35 and the numerical value 64 stored in the ROM.
n(V ₂ -V ₁ )/64 is calculated from the equation and the value is added to the adder 36. V1 is also added to the adder 36, and V shown in the above equation is determined from the value.
After finding the value of V for a certain n (n changes sequentially from 0 to 63 as described above), the same process is performed for the next two adjacent blocks in the scanning direction, leaving the value of n unchanged. Perform calculations to find V' in Figure 3. Similar calculations are then performed to find 49 interpolation points for one value of n to complete one scanning line. In this embodiment, one scanning line is created and at the same time two scanning lines are created as shown in FIG.
As soon as the calculation between the two blocks is completed, the interpolation circuit 1 in the main scanning direction (horizontal scanning direction), which will be described later, applies to the data that becomes an analog value via the D/A converter 15.
6 performs interpolation in the scanning line direction, and each control signal supplied from the system pulse generator 25
Analog data that has been interpolated under the control of H _S , V _S , P, H _B , and V _B is continuously supplied to modulators 17a, 17b, and 17c. Next, by changing the value of n, similar calculations are performed for n+1 to find adjacent scanning lines, and the same calculations are repeated to find 64 scanning lines between two blocks. Repeat this 31 times for each scanning line, and each
Obtain 64 scanning lines, completing a total of 1984 scanning lines. FIG. 5 is a block diagram showing the main scanning line direction interpolation method used in this embodiment. In the circuit shown in FIG. 5, the sample and hold circuit 39 holds the pixel data V ₁ before two pixels to be interpolated on one scanning line, and adds the difference between the pixel data V 1 and the subsequent pixel data V ₁ to the arithmetic unit 37. When this is calculated and added to the Miller integration circuit 38, data in which the distance between V ₁ ' and V ₁ changes almost linearly is output. As is well known, the Miller integrator circuit is a complete integrator circuit used for the generation of triangular or sawtooth waves.

The analog data that has been interpolated in the manner described above is sequentially sent to the modulator 17 for each of R, G, and B.
a, 17b, and 17c to perform R, G, and B shading correction. This modulator may be any circuit that provides characteristics inverse to the level of the correction data, and various methods may be used, but in this embodiment, a method of dividing the input signal by the correction data is adopted. In other words, when the input signal is E _IN and the coefficient representing the shedding effect due to the FSS tube and the camera's optical system is E _S , the signal that caused the shedding is given by E _IN E _S , so it can be divided by E _S. If so, use the principle that requires E _IN . FIG. 6 is a block diagram showing the modulation method in the modulator of the present invention. The circuit shown in FIG. 6 constitutes a division circuit by combining a multiplication circuit 40, an arithmetic circuit 41, and an amplifier 42. This modulator is supplied with H _S , V _S , and P signals as control pulses. When the input signal passes through this modulator, E _S is equal to the output signal of the main scanning correction circuit 16 when the aforementioned standard signal, that is, E _IN =1 is input, so E ₀ = E _IN /
By dividing by (1+E _S ), the input signal is modulated to have the opposite characteristics to the shading caused by the FSS tube and the optical system of the camera, that is, in a direction that corrects shading, and it is possible to expose the film with a light beam with almost no shading. can. Here,
E ₀ is the input signal of the modulator. The signal for which the shedding correction has been completed is further processed by correction circuits 18a and 1.
8b and 18c. In this correction circuit,
The film τ, the FSS tube τ, the input circuit characteristics, and the pedestal characteristics are each corrected, and the signals are supplied to the FSS tube separately for R, G, and B, and a photograph is taken using the method described above.

As explained in detail above, according to the present invention,
The shading of the FSS tube and the optical system of the camera can be corrected extremely precisely and quickly, and the frame memory for storing data is extremely small compared to the total number of pixels, making it possible to save memory. . Furthermore, the present invention can be used not only for photographing an image projected on an FSS tube, but also for other purposes in which it is necessary to accurately correct the shading of an FSS tube.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an example of the shading correction device of the present invention that corrects shading in a photographing device for images on an FSS tube, and Fig. 2 shows the screen surface of the FSS tube divided into blocks in the present invention. A diagram showing the state, FIG. 3 is a diagram showing the interpolation method in the sub-scanning direction between each section, FIG. 4 is a block diagram showing the logic circuit that executes the interpolation method shown in FIG. 3, and FIG. 6 is a block diagram showing a circuit that performs interpolation in the main scanning direction, and FIG. 6 is a block diagram showing a circuit that modulates an input signal with a correction signal. 1...FSS tube, 2...Mirror, 3, 6...R,
G, B filter, 4... Photographer, 5... Photographic film, 7... Correction optical system, 8... Photomultiplier tube, 9... Image signal processing circuit, 10... Buffer memory, 11... Average Value calculation circuit, 12... Frame memory, 13, 19... R, G, B changeover switch, 14... Sub-scanning line direction interpolation circuit, 15, 2
0...D/A converter, 16...Main scanning direction interpolation circuit, 17...Modulator, 18...Correction circuit, 21...
...Selector switch, 22...Test signal generator, 2
3...Line buffer, 24...Interface, 25...System pulse generator, 26
...Memory control, 27...FSS tube deflection coil.

Claims (1)

[Scope of Claims] 1. Means for generating a standard signal, means for receiving a raster image projected on a cathode ray tube surface by the standard signal, and means for transmitting the raster image into several pixels each including a plurality of pixels. a memory for dividing into ranges and storing representative values within the divisions as correction signals; means for reading and interpolating the correction signals in the memory to create a shading correction signal; and a modulator that gives the input signal characteristics opposite to the shading characteristics of the cathode ray tube, and the modulated output is applied to the brightness modulation terminal of the cathode ray tube to correct the shading of the cathode ray tube. Device. 2. A white standard signal, and red, green, and blue filters provided between the white raster image projected on the cathode ray tube surface by the white standard signal and the light receiving means;
means for switching the filter; a memory for separately storing red, green, and blue signals switched by the filter; a modulator for separately modulating the red, green, and blue signals; and a modulator for separately modulating the red, green, and blue signals; The shading correction signal according to claim 1, further comprising a correction means for correcting the shading correction signal. 3. means for generating a standard signal when a raster image projected on the cathode ray tube surface is photographed by a camera; and means for receiving the raster image projected on the cathode ray tube surface using the standard signal; A memory that divides the raster image into several ranges each including a plurality of pixels and stores representative values within the division as a correction signal, and reads out and interpolates the correction signal in the memory to generate a shading correction signal. a modulator that adds the input signal and the shading correction signal to provide a characteristic opposite to the shading characteristics of the cathode ray tube and the camera; and an optical system of the camera disposed between the surface of the cathode ray tube and the light receiving means. 1. A shading correction device comprising: an optical system having shading characteristics equivalent to the shading of the shading of the cathode ray tube, and the modulated output is applied to a brightness modulation terminal of a cathode ray tube to correct shading of the cathode ray tube and the camera. 4. A white standard signal, and red, green, and blue filters provided between the white raster image projected on the cathode ray tube surface by the white standard signal and the light receiving means;
means for switching the filter; a memory for separately storing red, green, and blue signals switched by the filter; a modulator for separately modulating the red, green, and blue signals; and a modulator for separately modulating the red, green, and blue signals; 4. The shading correction device according to claim 3, further comprising a correction means for correcting the shading.