JPH0681319B2 - Electronic image encoder - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color encoder for electronic image signals, and more particularly to a color encoder for converting an output image signal of an electronic image generating device into a television image signal of NTSC standard system. It is a thing.

(Prior Art) Conventionally, this kind of signal conversion device has been devised as a line adapter device for a personal computer. FIG. 3 shows a configuration block diagram of an example of a conventional device. The input side of this device is provided with an input terminal 1 for digital image signals (R, G, B), a horizontal sync signal input terminal 2, a vertical sync signal input terminal 3 and an external sync signal input terminal 4, and as a constituent block Sync signal generator 5, sync signal switcher 6, memory write signal generator 7, memory read signal generator 8, image memory 9, D / A converter 10 and R, G, B color image signals are converted to television signals. It is provided with an encoder 11 etc. for

The operation of this device is as follows. First, digital image signals of R, G, and B colors generated from an image generation device such as a personal computer are input from the input terminal 1, are generated from the same device, and are input via the input terminals 2 and 3. An image is generated by the memory write signal generated by the memory write signal generator 7 being controlled by the horizontal and vertical sync signals generated by the external sync input signal generated from another external device input through the input terminal 4. It is stored in the memory 9.

Next, the stored image signal is read by the read signal from the memory read signal generator 8 synchronized with the external sync signal from the sync signal generator 5, and then the D / A converter 10 is read.
Are converted into analog signals of R, G, and B colors by the encoder 11, converted into television image signals by the encoder 11, and output from the output terminal 12.

(Problems to be Solved by the Invention) As a problem of the conventional device, when observing an output image signal of this device on a monitor, visual flicker interference occurs in an image portion including a fine pattern or characters, There was a phenomenon that was perceived as deterioration of image quality. The reason for this is that the image generating device did not have a means for band limiting the vertical spatial frequency of the image, so that the high frequency component of the vertical spatial frequency causes aliasing distortion in the process of conversion to a television image signal, and it is visually 30 Hz.
Is sensed as a time-varying component of.

Let me explain this reason in some detail. FIG. 4 shows the relationship between the video signal spectrum and the aliasing noise spectrum generated by the interlaced scanning in two dimensions of the time frequency versus the vertical spatial frequency in the example of the NTSC television system. In the figure, a spectrum 23 is a video signal spectrum, an arrow spectrum portion 24 is a vertical spatial frequency high band component of the same spectrum, a point 25 is a two-dimensional sampling frequency due to interlaced scanning, and a broken line spectrum 26 is a folding noise spectrum. The arrow spectrum portion 27 corresponds to the aliasing noise component of the arrow spectrum portion 24. The existence of flicker disturbance having a temporal frequency component of 30 Hz is explained by the fact that the vertical spatial frequency high frequency component 24 of the video signal is folded back to the vertical spatial frequency low frequency component 27 having a temporal frequency component of 30 Hz by sampling. . That is, the flicker disturbance is sensed over a wider area on the screen as the video signal has a larger energy component in the higher vertical spatial frequency range.

Therefore, it is an object of the present invention to eliminate the above-mentioned conventional drawbacks and to provide an electronic image encoder with reduced visual flicker interference by adding a simple digital spatial frequency filter.

(Means for Solving the Problems) In order to achieve this object, the electronic image encoder of the present invention is
An electronic image encoder for converting an electronic image signal output into an image signal corresponding to the NTSC standard system is provided with a filter for reducing a high frequency component of a vertical spatial frequency of the electronic image signal output.

(Operation) The reason why the flicker interference is detected by the band limitation is as described above, but the reason why the interference is reduced by the present invention will be qualitatively described below.

FIG. 5 is an example of a simple black and white television image. The white level is 100 IRE and the black level is zero IRE. Looking at this image in the vertical direction, the image level distribution is the level distribution 28 in the figure.
It becomes like. In this example, the visual level difference between the even and odd fields is significant at position 29 in the figure, causing a large flicker disturbance. Here, like the level distribution 30 in the figure,
By smoothing the sharp level change between the white level and the black level by applying a low-pass filter for the vertical spatial frequency to the video signal, the visual level difference at the position 29 between the even and odd fields is reduced. This reduces flicker interference.

(Example) The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a block diagram of the configuration of an embodiment of the present invention.
In FIG. 1, the same components as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. In this configuration, an analog image signal input terminal 13, a band limiting filter 14 for band limiting, an A / D converter 15, an input switching section 16, a vertical spatial filter 17 and a horizontal spatial filter 18 are added to the configuration shown in FIG.

In this embodiment, an analog image signal input terminal 13 is provided so as to be compatible with an image generating apparatus such as a personal computer with an analog image output which has been popular in recent years. This input signal is further aliased and band-limited by the band-limiting filter 14 to avoid noise, then converted to a digital signal by the A / D converter 15, and the signal from the digital image signal input terminal 1 is input by the input switching unit 16. It is switched to. The image signal once recorded in the image memory 9 is read out by the means described in the conventional example, and then the vertical spatial frequency band is limited by the vertical spatial filter 17 to improve the flicker interference, and further, the horizontal spatial filter. By limiting the horizontal spatial frequency at 18, vertical and horizontal resolution isotropic is obtained.

FIG. 2 shows the configuration of the vertical and horizontal spatial filters used in the first illustrated embodiment. The second configuration is a one-line delay element
19 (H), coefficient multiplier 20, adder 21, and 1-sample delay element 22 (D). All of these constitute one transversal filter, and the coefficient gains K _H0 , K _H1 , K _H2 , ... K _Hi and K _D0 , K _D1 , K _{D2 of} the coefficient multiplier,
...... K _Dj is determined by switching the ROM, and the spatial frequency characteristics can be switched.

Note that if the high frequency components of the vertical spatial frequency are reduced too much, the overall image quality deteriorates due to the reduction in resolution.Therefore, while monitoring the encoder output image, set the above coefficient gains so that the overall image quality regarding flicker interference and resolution will be the best. adjust.

(Effects of the Invention) As described above, conventionally, no improvement measures have been taken against flicker interference that has occurred in the process of converting an electronically generated image into a television image signal. According to the encoder of the invention, the flicker interference is reduced by limiting the spatial frequency band by the spatial filter, and the frequency characteristic of the spatial filter is switched to a visually optimum one, so that the decrease in resolution is minimized and the television image The image quality can be comprehensively improved.

[Brief description of drawings]

FIG. 1 shows a block diagram of a configuration of an embodiment of an encoder of the present invention, FIG. 2 shows a detailed configuration diagram of vertical and horizontal spatial filters shown in FIG. 1, and FIG. 3 shows a configuration of an example of a conventional encoder. FIG. 4 shows a block diagram, FIG. 4 shows a diagram for explaining the reason why flicker interference occurs in a conventional example, and FIG. 5 shows a reason why flicker interference can be reduced by band limitation of vertical spatial frequency. The figure is shown. DESCRIPTION OF SYMBOLS 1 ... Digital image signal input terminal 2 ... Horizontal sync signal input terminal 3 ... Vertical sync signal input terminal 4 ... External sync signal input terminal 5 ... Sync signal reproducing section 6 ... Sync signal switching section 7 ... Memory write signal generating section 8 ... Memory read signal generator 9 ... Image memory, 10 ... D / A converter 11 ... Encoder, 12 ... Image signal output terminal 13 ... Analog image signal input terminal 14 ... Band limiting filter, 15 ... A / D converter 16 ... Input switching section , 17 ... Vertical spatial filter 18 ... Horizontal spatial filter 19 ... 1 line delay element (H) 20 ... Coefficient multiplier, 21 ... Adder 22 ... 1 sample delay element (D) 23 ... Spectrum, 24 ... Arrow spectrum part 25 ... Points, 26 ... Dotted spectrum 27 ... Arrow spectrum part 28, 30 ... Level distribution, 29 ... Position

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nagataki ▲ Tsutomu ▼ 4-23 Motomotogocho, Hachioji, Tokyo Videotron Co., Ltd. (72) Nobuyuki Tateishi 4th Motomotogo, Hachioji, Tokyo 14th-23rd Videotron Co., Ltd.

Claims (1)

[Claims] 1. An electronic image encoder for converting an electronic image signal output into an image signal corresponding to the NTSC standard system, comprising a filter for reducing a high frequency component of a vertical spatial frequency of the electronic image signal output. Electronic image encoder to do.