JPS62183265A - Image data transmission system - Google Patents

Abstract

PURPOSE:To prevent the deterioration in resolution due to the transmission of image data by converting an image converted into a digital image data into data in a way that the relation between the image data and the image density is linear at a gamma correction circuit independently of an image data reception section and sending the data. CONSTITUTION:An analog video signal is sent to an A/D converter 103, where the signal is converted into digital multi-value image data and gamma correction is applied so that the multi-value image data is linear to the original density according to the gamma correction of the gamma correction circuit 104. After processings such as edge emphasis, smoothing, conversion, trimming and movement are executed by an image processing circuit 105, the multi-value image data is compressed by a compression circuit 106 and an image is outputted to a transmission means 200. The image is stored in an image memory 301 having capacity by one page in an image data reception section 300, the data is restored to the original data by a multi-value image expansion circuit 303, and gamma correction is applied by the storage gamma correction circuit 304 in matching with the storage characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image data transmission system for exchanging digitized image data between transmitting and receiving devices.

[Prior Art] Conventionally, this type of device has been constructed as shown in FIG. That is, on the transmitting side 10, first, an electrical original image photoelectrically converted by an original reading unit 11 such as a CCD is digitized through an AMP 12 and an A/D converter 13, and is then digitized by a γ correction circuit 14.
γ correction is applied thereto and processed by the binarization circuit 15 or the dither circuit 16. Thereafter, an editing process such as scaling is performed as necessary in an editing processing circuit 17, and finally, the image data is compressed in an image data compression circuit 18 and sent to a transmission means 20 such as a public line network. On the receiving side 30, for example, if the recording device uses an electrophotographic process such as La5er Beam Printer, the transmitted image data is stored in the image memory 31, and then decompressed in real time by the image data decompression circuit 32. The processed and restored image data is given as a signal to the laser printer unit 34 via the laser driver 33, and is converted into light and recorded. In such a conventional system, firstly, the amount of information is reduced by binarizing or dithering the image data on the transmitting side, which has the disadvantage of causing image deterioration. Next, in order to express halftones, conventionally, a dither circuit 16 is used to form a set of a plurality of pixels as shown in FIG. 3, and this is done depending on the number of black pixels among the sets and the arrangement of the black pixels. Since each pixel could only be expressed as a binary value of black or white, shading was expressed using the area of a plurality of pixels as one unit, as described above. There are two drawbacks in this case, one is that 16 gradations are expressed in 4X4.
Since =16 pixels are required, the resolution drops to 1/4. In addition to the deterioration caused by the above-mentioned binarization process, this also causes deterioration due to gradation expression, resulting in a significant deterioration in the ability to express thin lines such as characters.

Second, since binarization processing or dither processing is performed on the transmitting side, there is no room for reprocessing or correction on the receiving side. In general, the gamma characteristics (relationship between the number of recorded dots or recording area vs. density) of the recording device on the receiving side depend on the recording method, such as electrophotography,
Depends on thermal, wire tod, etc. Therefore, in the conventional example, the characteristics of the recording device are considered on the transmitting side,
A γ correction circuit 14 must be provided to correct this characteristic. FIG. 5 shows a method for calculating the correction. The first quadrant converts the output from the CCD into the A/D converter 13.
In general, the density of the original and the quantized data are not linear, and the density of the original has a characteristic that the amount of change is small when the density of the original is high, and the amount of change is large when the density of the original is light. The third quadrant is the relationship between the number of recorded dots per unit area and the recording density corresponding to the quantized data manually generated on the recording side, and this example shows the characteristics of the electrophotographic method. The fourth quadrant is the relationship between the original density and the recording density, and is the target value of output, which is generally set to be linear in order to output faithfully. The gamma correction value is obtained by plotting the second quadrant from the first, third, and fourth quadrants.

However, in reality, the recording devices on the receiving side that receive and output data are made by different manufacturers and have different recording methods. It's almost impossible to leave it behind. Therefore, the conventional method has a drawback in that it is impossible to output an optimal halftone image regardless of the combination of transmitting and receiving devices. The present invention focuses on the fact that conventional binarization processing and dithering processing for expressing halftones degrades resolution and creates communication constraints, and uses separate processing for photographs and 8 characters. Instead, we propose a method that can express text and photographs using basically the same processing, and that can output to unspecified types of recording devices.

[Problems to be Solved by the Invention] Therefore, the present invention eliminates the conventional drawbacks, prevents resolution deterioration due to image data transmission, and makes it possible to adjust the gradation of a halftone image using any combination of transmitting and receiving devices. To provide an image data transmission system that does not lose data. Furthermore, the present invention provides an image data transmitting device capable of processing without being aware of the recording characteristics of the receiving side, and an image data receiving device capable of processing without being aware of the reading characteristics of the transmitting side, which realize the image data transmission system. .

[Means for Solving the Problem] As a means for solving this problem, an image data transmission system includes an image data transmission section 100, an image data transmission means 200, and an image data reception section 300. .

Here, the image data transmitting section 100 includes the document reading section 101
, an amplifier 102 , an A/D converter 103 , a γ correction circuit 104 , an image processing circuit 105 , a multivalued image data compression circuit 106 , a binarization circuit 107 , and a binary image data compression circuit 108 , an image area recognition circuit 109 , a switching circuit 110 , and a tone variable dial 111 .

Further, the image data receiving section 300 includes an image memory 301,
Auxiliary memory 302 and multivalued image data expansion circuit 303
, a recording γ correction circuit 304, a PWM circuit 305,
Switching circuit 306, laser driver 307, laser printer section 308, binary image expansion circuit 309, CRT gamma correction circuit 310, brightness modulation circuit 311, CRT 312, mouse 313, tone variable dial 314.

[Function] In this configuration, the image data transmitting section 100 is connected to the document reading section 101. Amplifier 102. A/D converter 103
The image converted into digital image data is converted in the γ correction circuit 104 so that the relationship between the image data and the image density has a linear characteristic, regardless of the image data receiving section 300, and is transmitted.

On the other hand, the image data receiving section 300 includes the image data transmitting section 1
00, it is assumed that the relationship between the received image data and the image density has a linear characteristic, and the recording γ correction circuit 304 and the CRT r correction circuit 310 perform conversion according to the output device. Achieve optimal output.

[Example] In the image data transmission system of this example, the transmitting side transmits digital multi-value image data without performing binarization processing or dither processing, and the receiving side transmits the received multi-value image data. This gives you the freedom to perform any processing that suits your recording device's characteristics and convenience.

Then, assuming that the transmitting side does not know what kind of device the receiving side is, the γ correction value is set so that the γ characteristic at the time the transmitter outputs is linear, and the γ correction value on the receiving side is determined by the input image data. The γ characteristic of is set on the assumption that it is linear. The above situation is shown in Figure 6.7. 6th
The figure shows the rules for setting the γ correction value on the transmitting side. The third quadrant is the relationship between the multivalued image data output from the transmitting side and the recording density given by the single characteristics of the recording side, and the fourth quadrant is the original density, which is the final image performance obtained from all of the transmission → reception recording. and recording density, and assuming that both are linear on the transmitting side, a γ correction curve in the second quadrant is set.

Then, this curve becomes a curve that corrects the A/D converter output value of the image sensor in the first quadrant so that it becomes completely linear.

Next, FIG. 7 shows the rules for setting the γ correction value on the recording side. The characteristics of the output multivalued image data and the recording density in the third quadrant are unique to the apparatus, and this example shows an electrophotographic type. The final output of the fourth quadrant can be changed according to preference, but in this example it is linear. Next, the first quadrant shows the characteristics of the A/D converter output value of the image sensor, but in this example, it is assumed that this is linear due to the γ correction operation shown in FIG. 3. The γ correction value in the second quadrant can be calculated from the data in the fourth quadrant.

Therefore, one of the features of this embodiment is that the respective γ correction values are determined on the premise that the third quadrant on the transmitting side and the first quadrant on the receiving side are linear.

Next, the image data transmission system of this embodiment will be explained according to the system block diagram of FIG. Image data transmitter 10
0, an analog video signal read by an image sensor in a document reading section 101 is sent to an A/D converter 103 via an amplifier 102 and converted into digital multi-value image data. In this example, it is converted to 4-bit multivalue (16 gradations). Furthermore, the γ correction value determined according to the rules shown in FIG. 6 described above is written in the γ correction circuit 104, and γ correction is performed in accordance with this value so that the multi-valued image data with respect to the original density becomes linear. The γ-corrected multi-valued image data is subjected to processing such as etch enhancement, smoothing processing, conversion processing, trimming, and movement in the image processing circuit 105. After that, the multi-valued image data is compressed in the compression circuit 106 and transmitted. The image is output to means 200. Note that vector quantization, which was previously proposed in Japanese Patent Application No. 60-281640, is used to compress this multivalued image data.

However, the problem with the transmission of multivalued image data is that the facsimile standard is not standardized by CCITT Group 3 or 4. If you try to communicate over this line, the only option left is to use the optional mode, and even if you do, image data can only be exchanged between specific models. In addition, even if multilevel image data is compressed, the amount of data is overwhelmingly larger than binary data, which increases the cost and capacity of media such as transmission lines and memory.
Considering the case where priority is given to image quality over image quality, a binarization circuit 107, MH is used to perform binarization processing or dither processing in parallel with compression of multivalued image data, and further to compress the data. , Binary image compression circuit 1 using MR encoding
08 is provided. Then, a switching circuit 110 for switching between binary image data and multi-value image data is provided.
Line drawings can be selected according to line and memory capacity), and line drawings can be recorded in binary format, while photographs can be recorded in multi-level format. Furthermore, by operating an image area recognition circuit 109 that automatically recognizes line drawings and photographic parts in the document in parallel with the above processing, and switching the switching circuit 110 on a pixel-by-pixel level based on the recognition result, It is possible to obtain high quality images with less information than when transmitting everything in multi-level format.

Regarding the next image data receiving section 300, in this example, the recording method will be described as a laser electrophotographic method. First, multivalued image data having a linear γ characteristic is stored in an image memory 301 having a capacity of at least one page. This data can be stored in, or loaded from, a large capacity auxiliary memory 302 such as a disk memory.

This is to provide convenience for searching multiple pages of images sent to you as files. The multivalued image data on the image memory 301 is normally restored to the original data by the multivalued image decompression circuit 303 and then sent to the recording γ correction circuit 304.
γ correction is performed according to the recording characteristics. This γ correction value is set to a value determined by the rules shown in FIG. The γ-corrected multivalued image data is pulse width modulated in accordance with the image density by a PWM circuit 305, and is again applied to the laser 307 as an analog density signal. This pulse width modulation recording is illustrated in FIGS. 4(a) and (b).

In Figure 4(a), an elongated laser spot whose width is sufficiently smaller than the recorded size of one pixel (the rectangle surrounded by a dotted line) is scanned in the width direction, and the laser spot is scanned in the width direction within the time corresponding to the width of one pixel. The lighting time is determined based on multivalued image data. In this example, one pixel density is 4
Since it is expressed in bits, there are 16 levels of lighting time. In other words, as shown in part in Figure 4(b), each pixel is represented by a spot with 16 different widths, so unlike only white and black in the case of binarization, within one pixel It is possible to express halftones, and as a result, it is possible to record high-definition text and photographs. or,
In this example, CR is used to search and process the restored image data.
The multivalued image data is passed through a CRT gamma correction circuit 310 having a gamma correction value matched to the gamma characteristics of the CRT so that it can be output on the T312, and then subjected to analog brightness modulation by an analog brightness modulation circuit 311. In addition, a tone variable dial 314 is provided so that the operator can change the tone of the image by operating the keyboard or mouse 313 while looking at the image on the CRT.
By simultaneously accessing the correction circuit 310, the CR
The same tone as seen in T can be reproduced in recording. or,
It has been described that the transmitting side 100 is provided with the binarization circuit 107, but correspondingly, the receiving side 300 is provided with a binary image data decompression processing circuit 309 in parallel with the multivalued image data decompression processing circuit 303. , and a switching circuit 30B is also provided so that multi-value and binary data can be switched based on control information from the transmitting side. In addition, a tone variable dial 111 is provided that allows the gamma correction circuit 104 on the transmitting side 100 to select a gamma correction value. If the tone variable dial 114 is fixed for each device, the dial 111 is fixed for each device, and the dial 111 is fixed for each device. It can be used as a variable density dial.

In this embodiment, the case where the image data transmitting section and the image data receiving section are connected by one transmission means has been described, but when multiple transmitting sections and receiving sections are connected on a network or a public line etc. When connected to an unknown transmitter or receiver, an even greater effect is produced.

As described above, since the conventional dither method is not used, there is no deterioration in resolution, and halftone images can be faithfully transmitted.

Furthermore, by making the γ characteristics linear in terms of transmission and reception, the transmitting side does not need to consider the receiving side's γ characteristics in any combination of transmitting and receiving devices, and the receiving side does not need to consider the γ characteristics of the receiving side. Regardless, the best image can be obtained by performing a γ correction operation that matches the recording characteristics of the recording apparatus.

In addition, the standard transmission of conventional G3/G4 binarization and o
By combining this with multilevel transmission using option mode, it is possible to provide standard FAX with the possibility of high-quality transmission.

In addition, it is possible to change the tone of the image received on the receiving side according to one's preference and output it.

[Effects of the Invention] According to the present invention, it is possible to provide an image data transmission system that prevents deterioration of resolution due to transmission of image data and that does not lose the gradation of a halftone image regardless of the combination of transmitting and receiving devices. Furthermore, the present invention provides an image data transmitting device capable of processing without being aware of the recording characteristics of the receiving side, and an image data receiving device capable of processing without being aware of the reading characteristics of the transmitting side, which realize the image data transmission system. .

[Brief explanation of drawings]

Figure 1 is a system block diagram of the conventional example, Figure 2 is a system block diagram of this embodiment, Figure 3 is an explanatory diagram of the dot growth mechanism of the conventional dither method, Figures 4 (a) and (b) is an explanatory diagram of halftone expression by pulse width modulation, Fig. 5 is an explanatory diagram of the conventional γ correction value setting rule, Fig. 6 is an explanatory diagram of the setting rule on the transmitting side of this embodiment, and Fig. 7 is an explanatory diagram of the present embodiment. FIG. 3 is an explanatory diagram of setting rules on the receiving side. In the figure, 101... document reading section, 102... amplifier,
103... A/D converter, 104... γ correction circuit, 105... Image processing circuit, 106... Multivalued image data compression circuit, 107... Binarization circuit, 108...
...Binary image data compression circuit, 10.9... Image area recognition circuit, 110... Switching circuit, 111... Tone variable dial, 200... Image data transmission means,
301... Image memory, 302... Auxiliary memory, 3
03... Multivalued image data expansion circuit, 304... Recording γ correction circuit, 305... PWM circuit, 306...
・Switching circuit, 307... Laser driver, 30
8... Laser printer section, 309-... Binary image expansion circuit, 310... CRT γ correction circuit, 311 Multi-value image data brightness modulation circuit, 312... CRT, 31
3...Mouse, 314...Tone variable dial. Patent applicant: Canon Co., Ltd. Figure 6 O Figure 7 p

Claims (3)

[Claims] (1) An image data transmission system that transfers digitized image data between transmitting and receiving devices, characterized in that the characteristics of the transmitted image data are kept almost linear. (2) The image data transmission system according to claim 1, wherein the characteristic of the image data is a density characteristic. (3) The image data transmission system according to claim 1, wherein the density characteristic is a γ characteristic.