JPH0218789B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image signal contour correction method for correcting the contour of an image by compensating for the high-frequency characteristics of an image signal such as that output from a television camera, and particularly relates to a method for correcting the contour of an image by digitally processing the image signal. Even if contour correction is applied, the analog
This is to prevent image quality deterioration due to digital conversion.

Prior Art This type of conventional image signal contour correction method has exclusively
Signal processing for contour correction was performed on analog image signals, but when performing digital processing on image signals, so-called gamma correction was performed after performing analog-to-digital conversion on the image signals to perform contour correction. In other words, in conventional digital processing of image signals, the number of quantization levels of the analog-to-digital converter is finite. ,
By performing non-linear signal level processing of gamma correction in a process amplifier, the gradation characteristics of low-level portions of the image signal, that is, dark portions, become coarse, resulting in deterioration of image quality.

Summary of the Invention An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional art, and to solve the problem of image quality deterioration even when analog-to-digital conversion is performed after nonlinear signal level processing for gamma correction is performed on an image signal in advance. It is an object of the present invention to provide an image signal contour correction method that performs contour correction on an image signal in such a manner that there is no distortion, and takes advantage of the advantages of image signal digital processing.

That is, the image signal contour correction method of the present invention includes an analog-to-digital converter that converts an input analog image signal into a digital image signal, and a method for sequentially converting the digital image signal converted by the analog-to-digital converter into a predetermined period of time. a plurality of delay circuits for delaying, a plurality of level corrections for multiplying signal levels of the digital image signal converted by the analog-to-digital converter and each delayed output image signal of the plurality of delay circuits by predetermined coefficients; and a plurality of adders that sequentially add the level correction outputs of the plurality of level correction means. After performing gamma correction to compress the high level part, the signal is supplied to the analog-to-digital converter and converted into a digital image signal. A table in which correction results in a direction opposite to the gamma correction are stored in advance in correspondence with the input level of the level correction means, and data corresponding to the input signal is read out using the input signal as an address. - It is characterized in that signal processing is performed by applying the lookup method.

EXAMPLES The present invention will be explained in detail below using examples with reference to the drawings.

First, when performing vertical contour correction on an analog image signal, conventional image signal contour correction devices perform contour correction signal processing and then gamma correction non-linear signal level processing. The configuration is shown in Figure 1. In the conventional configuration shown,
First, the captured output image signal from the television camera 1 is sequentially supplied to delay circuits 2 and 3 for one horizontal scanning period, and is delayed by one horizontal scanning period.
The image signals at the input point A and output point C of the series-connected delay circuits 2 and 3 are added by the adder 4, and the added output signal is supplied to the coefficient unit 5 to calculate the coefficient (-
1/2) to invert the polarity and halve the signal amplitude. Next, when the output signal of the coefficient unit 5 and the image signal at the intermediate point B of the series-connected delay circuits 2 and 3 described above are added by the adder 6, the contour correction signal component is obtained at the output point D of the adder 6. can get. After the signal amplitude of this contour correction signal component is appropriately adjusted by a gain adjuster 7, it is guided to an adder 8, and is fed to the above-mentioned series-connected delay circuits 2 and 3.
is added to the image signal delayed by one horizontal scanning period at the midpoint B to form a contour-corrected output image signal, and then the contour-corrected output image signal is led to the gamma correction circuit 9 to correct the non-linearity of the signal amplitude. Make corrections.

FIG. 2 shows an example of the configuration of the image signal contour correction device according to the present invention, in contrast to the conventional configuration shown in FIG. 1 described above. In the illustrated configuration example, the imaging output analog image signal from the television camera 10 is
First, after non-linear signal level processing is performed by the gamma correction circuit 25, the digital image is supplied to the analog-to-digital converter 12 via the band-limiting low-pass filter 11 and subjected to contour correction. Convert to signal. Then, the digital image signal is sent to one horizontal scanning period delay circuits 13 and 14, as in the conventional configuration shown in FIG.
are sequentially supplied and delayed by one horizontal scanning period. The digital image signals at the input point E, intermediate point F, and output point G of the series-connected delay circuits 13 and 14 are supplied to each coefficient unit 15, 16, and 17, respectively, to obtain a required coefficient value, for example, a coefficient value ( −
Multiply by 1/2, coefficient value (1), and coefficient value (-1/2), respectively. Next, the output signals of the coefficient units 15 and 16 are added together in an adder 18, and the adder 18
The addition output signal and the output signal of the coefficient multiplier 17 are added by an adder 19, and a contour-corrected digital image signal component is obtained at the output point H of the adder 19.
Next, the contour correction output digital image signal component is supplied to an overflow/underflow processing circuit 20 to clip and remove signal components exceeding a predetermined level range, and then supplied to a gain adjuster 21 to adjust the signal amplitude. After making appropriate adjustments, adder 2
2 and the above-mentioned series connected delay circuit 13,1.
The digital image signal component delayed by one horizontal scanning period from the midpoint F of 4 is added to the digital image signal component delayed by one horizontal scanning period from the midpoint F of 4. It is taken out through the pass filter 24.

As can be seen from the above explanation, in the conventional device, gamma correction is applied after contour correction, whereas in the device according to the present invention, the image pickup output analog image signal is After applying gamma correction, it is converted to a digital image signal, and contour correction is applied by skillfully utilizing the advantages of digital signal processing technology, so as described below, the disadvantages of the conventional image signal are eliminated. This will result in a significant effect.

That is, first of all, there is a practical limit to the number of bits of a digital image signal that can be obtained with an analog-to-digital converter, and it is difficult to realize a converter with a 10-bit configuration as an image signal processing converter.
Generally, an 8-bit configuration is considered to be the practical limit. However, when nonlinear signal level processing is applied to an image signal with an 8-bit configuration, the quantization of the signal level in the low-level, low-brightness area becomes rougher in the case of gamma correction that compresses the high-level area, resulting in poor image quality. deteriorates. Therefore, in the apparatus according to the present invention, an analog image signal obtained by gamma-correcting the camera image output image signal is used as the main image information signal. In the main line system shown by the bold line in Fig. 2, the image signal that has been subjected to gamma correction is passed through, so nonlinear image signal processing is not performed again, and analog-to-digital conversion and digital conversion are simply performed.
Only analog reconversion is performed, and as will be described later, contour correction accompanied by inverse gamma correction is performed only in a peripheral contour correction system (hereinafter simply referred to as the correction system).
As a result, the 8-bit digital image signal is reconverted directly into an analog image signal, so
No deterioration in image quality occurs at all.

Next, when extracting the contour correction signal component while keeping the linear configuration in the correction system, you will notice that the input analog image signal is an analog image signal that has been subjected to non-linear processing of gamma correction, so the low-level, low-luminance The image signal component of the area is emphasized, and a contour correction signal larger than that of the high-level part is generated for the noise mixed in that area, and as a result, the noise in that area is emphasized.

Therefore, the signal-to-noise ratio in the low-level, low-luminance region will deteriorate. On the other hand, the contour correction signal for the high-level portion becomes small, and the contour of the image in the high-level portion is not emphasized. In order to avoid such deterioration of image quality, in the apparatus according to the present invention, the coefficient unit used for contour correction is configured with a storage element such as a random access memory (RAM) or a read-only memory (ROM), and the gamma correction is performed. Make the reverse correction. That is, data covering the entire required range is stored in advance in a storage element constituting a coefficient unit, and data corresponding to the input signal is read out using the input signal as an address.
Inverse gamma correction signal processing is performed by executing a multiplication process of "predetermined coefficient x variable" using a so-called table lookup method. Therefore, with the coefficient unit having such a configuration, it is possible to simultaneously perform nonlinear signal processing for inverse gamma correction and coefficient value multiplication for contour correction using the table lookup method. A good contour correction signal component can be obtained without deterioration of the noise-to-noise ratio.

In addition, the gain adjuster that adjusts the signal amplitude of the contour correction signal component to the required value is also configured with random access memory or read-only memory, and nonlinear signal processing such as coring is performed to further suppress deterioration of the signal-to-noise ratio. can be performed simultaneously with gain adjustment, and as a result, a contour-corrected image signal component with further improved performance can be obtained.

Note that when coring processing is performed in a digital processing system, much more stable signal processing can be performed than when coring processing is performed in an analog processing system.

Effects As is clear from the above explanation, according to the present invention, only linear processing of the image signal is performed in the main line system that transmits the imaging output image signal subjected to non-linear correction as image information, and the non-linear processing of the gamma correction Since the processed analog image signal is simply digitized and then reconverted into an analog image signal, the quantization accuracy of the main line digital processing can be maintained while maintaining the quantization accuracy of the input analog-to-digital converter. It is possible to reconvert the image signal into an analog image signal at , and it is possible to perform contour correction of good image quality on the image signal without deteriorating the image quality due to a reduction in the equivalent number of bits.

In addition, in the correction system added as a side system to the above-mentioned main linear system, nonlinear image processing for inverse gamma correction is performed simultaneously with coefficient multiplication processing for contour correction using a coefficient unit for contour correction. A contour-corrected image signal component of good image quality can be obtained without deterioration of the signal-to-noise ratio in the brightness region and without insufficient contour correction in the high-brightness region.

Furthermore, regarding the one horizontal scanning period delay circuit,
The analog signal processing system of conventional equipment uses an ultrasonic delay line, so it is extremely difficult to eliminate unstable factors such as fluctuations in delay time due to temperature changes and ghosts caused by spurious components. Since the digital signal processing system of the apparatus according to the invention uses shift registers and the like that operate extremely stably, it is possible to realize a contour correction method having extremely excellent overall characteristics.

Note that in the above description, the apparatus according to the present invention has been described exclusively with respect to an example in which a one horizontal scanning period delay circuit is used when forming a vertical contour correction signal component, but the present invention is not limited to this example. Without,
The same effect as described above can be obtained when a delay circuit in units of clock cycles is used when forming the horizontal direction contour correction image signal component. Even in the case of application, similar effects can be obtained by using the same structure.

Furthermore, regarding the nonlinear characteristics used for inverse gamma correction, it is possible to use nonlinear characteristics intentionally and appropriately shifted from the gamma characteristics of the image output image signal captured by a television camera; It has become clear that better image quality can be improved by using an inverse gamma characteristic that has a slightly smaller value than the nonlinear characteristic that is exactly inverse to the gamma characteristic.

In addition, special image effects can be obtained by making the characteristic curve of the contour correction coefficient unit a nonlinear curve that is significantly different from the inverse gamma characteristic curve.
For example, it is also possible to perform contour correction only on high-brightness areas of the screen.

Note that since the side correction system in the apparatus according to the present invention extracts image signal components corresponding to the edge portions of an image, such signal correction according to the present invention is applied to a circuit device that requires such edge portion image signal components. By using this system, edge image signal components with an excellent signal-to-noise ratio can be extracted by a digital signal processing system.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional image signal contour correction device, and FIG. 2 is a block diagram showing an example of the configuration of the image signal contour correction device according to the present invention. 1,10...TV camera, 2,3,1
3, 14...1 horizontal scanning period delay circuit, 4, 6,
8, 18, 19, 22... Adder, 5, 15, 1
6, 17... Coefficient unit, 7, 21... Gain adjuster,
9, 25... Gamma correction circuit, 11, 24... Low pass filter, 12... Analog/digital converter, 20... Overflow/underflow processing circuit, 23... Digital/analog converter.

Claims (1)

[Claims] 1. an analog-digital converter that converts an input analog image signal into a digital image signal; a plurality of delay circuits that sequentially delay the digital image signal converted by the analog-digital converter by a predetermined cycle; analog·
a plurality of level correction means for multiplying the signal level of the digital image signal converted by the digital converter and each delayed output image signal of the plurality of delay circuits by predetermined coefficients; When forming a contour correction signal by a contour correction system comprising a plurality of adders that sequentially add level correction outputs, gamma correction is applied to the input analog image signal to compress its high level part. Later, the signal is supplied to the analog-to-digital converter and converted into a digital image signal, and the plurality of level correction means performs multiplication by the respective predetermined coefficients and correction in the direction opposite to the gamma correction. Each correction result is stored in advance in correspondence with the input level of the level correction means, and signal processing is performed by applying a table lookup method in which data corresponding to the input signal is read out using the input signal as an address. An image signal contour correction method characterized by: