JPH0544877B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field Related to the Invention The present invention provides an A/D converter for converting an analog video signal sent from a video signal generator (photoelectric conversion) into a digital video signal. , relates to a digital video signal processing device.

When processing digital video signals, the use of 8-bit digital signals has proven effective and sufficient in most cases. This number of bits is sufficient to considerably reduce quantization effects if the video signal is A/D converted after gamma correction has already been performed.
However, if the analog video signal sent from the video signal generator is A/D converted before gamma correction, the quantization may not be visible to the naked eye in dark image areas under the same number of bits. You will be able to do it. This is because gamma correction corresponds to signal amplification in this region. As is known, the non-linear relationship between the luminous efficiency and the electrical control signal supplied to the television picture reproduction tube is compensated, for example in a television camera, by an inverse signal modification according to a so-called gamma characteristic curve. The video signal corresponding to the dark image area must therefore be converted with a resolution of at least 10 bits, above the usual 8 bits, if starting from a linear A/D conversion. On the other hand, in bright image areas, a resolution of 7 bits is sufficient. Therefore 10
The disadvantage of using a bit A/D converter is that it is not possible to take advantage of the high image quality of the video signal, which corresponds to bright image areas. Moreover, such converters for video technology are too expensive and bulky and are currently hardly available.

As a way to avoid these difficulties, the magazine "Journal of the SMPTE" December 1980 issue,
From pages 938 to 942, especially page 939, it is already known to use two 8-bit A/D converters. In that case, the second A/D converter is supplied with an eight-fold amplified analog video signal. This second A/D converter sends out a digital signal only when the analog input signal is 12.5% below the white level. In this case, an additional 3-bit signal is obtained. However, this known method has the disadvantage of being relatively expensive.

[Object of the Invention] Therefore, it is an object of the present invention to solve the problems of the prior art that occur when A/D conversion is performed, and to perform high-resolution A/D conversion of a video signal before the gamma correction. The object of the present invention is to achieve a D-conversion device configuration with a small circuit technology cost.

[Configuration and Effects of the Invention] To solve the above problems, the present invention provides an A/D converter for converting an analog video signal sent from a video signal generation period (photoelectric conversion) into a digital video signal. In a digital video signal processing device equipped with the above, in order to A/D convert the video signal with high resolution before the gamma correction, a characteristic curve approximately corresponding to a so-called gamma characteristic curve to which an analog video signal is supplied is provided. A/D with
a converter and a memory having a characteristic curve opposite to that of the converter configured to linearize the output signal of the A/D converter and expand the word length (word width); The arrangement is such that after the digital conversion, a word having a higher bit width (bit length) than the A/D converter itself is obtained, and the digital video signal thus obtained is fed to a processing stage known per se,
The processed digital video signal is fed to a digital gamma stage, where the digital gamma stage
From the output of the gamma stage, the video signal is transformed according to the desired gamma function and the word length is shortened.
It is arranged to extract a gamma-corrected digital video signal whose word length corresponds to the output signal of the converter.

The device according to the invention with the features as claimed in claim 1 has the following advantages. In other words, one A/D converter that is currently available at low cost.
By using only one, it is possible to achieve a resolution that is advantageous for digital processing of video signals. In this case, it is assumed that a high resolution is required in a small voltage region, whereas a low resolution is sufficient in a high voltage region. There is also the advantage that the gamma characteristics can be well approximated to appropriate converter characteristics, thereby allowing optimal use of the converter characteristics.

It is particularly advantageous if the memory and the gamma stage are each configured as a write/continue memory. By doing so, the characteristics of the memory can be changed during operation, when the characteristics of the adjusted converter are slightly off, or when using different A/D converters corresponding to different changes. It can be matched to the characteristics of the container. Such matching of memory characteristics can be done manually or by microprocessor control.

DESCRIPTION OF EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

In the figure, a channel of a black and white television camera or a color television camera or a video signal path of a color film scanner is shown. Terminal 1 is supplied with an analog video signal which is output by a photoelectric converter (not shown) and is optionally amplified. This video signal is converted into a digital 8-bit video signal by an A/D converter 2 having a nonlinear characteristic curve. For nonlinear transformation,
For example, TRW LSI Products' “Digital Signal
As described in "Processor" Vol. 1, No. 1, April 1980, high resolution can be obtained in a low voltage region, and a correspondingly low resolution can be obtained in a high voltage region. In order to achieve as uniform a resolution as possible after gamma correction, the characteristic curve of the converter should be matched to the gamma characteristic curve. This characteristic curve is obtained by appropriately selecting the resistors 3, 4 that define the characteristic curve, and the deviations are negligible. At that time, the resistor 4 is connected to the terminal 6
is connected to a reference voltage source via.

The digitized video signal has a nonlinear relationship to the analog input video signal, but signals that are linearly dependent on the input signal can be processed well, so first linearize the digitized video signal. There must be. This is most simply carried out by means of a downstream fixed memory (ROM) 7. This fixed memory (ROM)7
has a characteristic curve opposite to that of the transducer. In this case, the address of the memory 7 is formed by an 8-bit input data word, and at the data output of the memory 7 a function value corresponding to the inverse characteristic curve can be retrieved. In this case, the data length is expanded to 10 bits to avoid resolution loss.

This 10-bit digital signal is processed in a known manner in a video signal processing stage 8. For example, at that time, fault signal correction and matrix processing are performed.

The processed 10-bit video signal taken from the output of the video signal processing stage 8 is then supplied to a digital gamma correction stage (ROM) 9. In this digital gamma correction stage (ROM) 9, transformation is performed according to a desired gamma function, and the data length is shortened to 8 bits. Therefore, output terminal 1
1, a digital 8-bit long, gamma-corrected video signal is extracted for processing.

Instead of fixed memory (ROM) stages 7, 9, write/read memory (RAM) with variable characteristics can also be used. By doing so, various changes in the characteristics of the converter can be compensated for.

[Brief explanation of drawings]

The figure is a schematic circuit diagram of an embodiment of the invention. 2...A/D converter, 7...Memory (ROM),
8...Video signal processing stage, 9...Gamma stage.

Claims (1)

[Claims] 1. A digital video signal processing device equipped with an A/D converter for converting an analog video signal sent from a video signal generator (photoelectric conversion) into a digital video signal. In order to A/D convert the video signal with high resolution before gamma correction, an A/D converter 2 is provided which has a characteristic curve approximately corresponding to the so-called gamma characteristic curve to which the analog video signal is supplied. /D converter 2
A memory 7 is provided, which has a characteristic curve opposite to that of the converter, which is configured to linearize the output signal and expand the word length (word width), so that after the digital conversion, the It is arranged in such a way that a word having a higher bit width (bit length) than the A/D converter itself is obtained, and the digital video signal thus obtained is fed to a processing stage known per se for processing. The resulting digital video signal is supplied to a digital gamma stage 9, which transforms the video signal according to a desired gamma function and shortens the word length, and outputs the video signal from an output terminal 11 of the gamma stage 9. A digital video signal processing device, characterized in that it is configured to take out a gamma-corrected digital video signal, the word length of which corresponds to the output signal of the converter. 2 The A/D converter 2 generates an 8-bit digital output signal, and stores the length of the signal in the memory 7.
is enlarged to 10 bits, and gamma step 9
2. A digital video signal processing apparatus according to claim 1, wherein the digital video signal processing apparatus is arranged for shortening to bits. 3. The digital video signal processing device according to claim 1, wherein the memory 7 and the gamma stage 9 are each configured as a fixed memory (ROM). 4. Digital video signal processing device according to claim 1, wherein the memory 7 and the gamma stage 9 are each configured as a write/read memory (RAM).