JP2002044463A - Color facsimile machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color facsimile machine which can realize trade-offs between communication time and image quality, in a color facsimile machine which can transmit data of color image via a communication line. SOLUTION: When image data 201 of a digital camera are transmitted with the color facsimile machine 1, the color space of the image data 201 of an electronic still camera is different from a color space to be transmitted to a communication channel with the facsimile machine 1, so that the image data 201 of the digital camera must be once decoded, subjected to color conversion and are re-encoded. Hence, data size prior to decoding is stored, and a compression factor is selected from the amount of data in the case of encoding. The compression factor is selected, by preparing a plurality of sampling ratios used in sampling 210 and quantization tables 213 used in quantization 212 and changing them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color facsimile apparatus for compressing and transmitting a color image input from an image input device.

[0002]

2. Description of the Related Art Conventionally, a color facsimile apparatus uses a so-called JPEG as a color image compression method.
(Joint Photographic Coding Experts Group) Compression and the like are used. Since a color image has a larger amount of image data than a black and white binary image, it takes time to transmit the image data. Therefore, when transmitting a color image by JPEG compression via a communication line, Japanese Patent Laid-Open No. 8-84259
In Japanese Patent Application Laid-Open Publication No. H10-157, a part of an image is binarized using image information of an input image as a means for shortening communication time, and JBIG (Jo
A method of performing transmission after performing int-bi-level image coding expert group (encoding) is disclosed. In addition, Japanese Unexamined Patent Publication
Japanese Patent Application Laid-Open No. 92491 discloses a method for compressing image data using JPE.
G, JBIG, MR (Modifide Read), MMR (Modif
ide ModifideRead) and a method for transmitting image data.

[0003]

However, in Japanese Patent Application Laid-Open Nos. 8-84259 and 6-92491, a part of an image is binarized to shorten the communication time, or the encoding method itself is disclosed. The selection merely binarizes the image to reduce the communication time, and eliminates uniform JPEG mode encoding. Also, in these publications, to reduce the communication time in transmitting color images, it is sufficient to increase the encoding compression ratio, but conversely, the communication time in transmitting color image data is degraded, for example, image quality is reduced. No mention is made of the trade-off between shortening and image quality.

In general, when an original is read by a color scanner and transmitted by a facsimile apparatus, an image input to the facsimile apparatus is R (Red) G (Green) B
(Blue) data. The read RGB data is
Regarding the PEG compression, regardless of the data amount of the input image is the same, regardless of the characteristics of the image, JP
Since the data amount of the image after EG compression is different, JP
It has been difficult to set a trade-off between communication time and image quality by setting the EG compression ratio in advance and automatically setting the compression ratio in the device.

It is an object of the present invention to provide a color facsimile apparatus capable of transmitting and receiving color image data via a communication line and capable of achieving a trade-off between communication time and image quality.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a color facsimile apparatus for compressing a color image input from an image input device and transmitting the compressed color image to a partner device via a communication line.
A color facsimile apparatus comprising: an acquisition unit that acquires the data amount of the color image; and a compression ratio selection unit that selects a compression ratio based on the acquired data amount of the color image.

According to the present invention, the data amount of an image input from an image input device is stored, and the image compression rate is determined based on the data amount of the image at the time of encoding. In other words, when the image data amount is small, the compression ratio is reduced to give priority to the image quality of the transmission image, and when the image data amount is large, the compression ratio is increased to shorten the communication time. Thus, instead of simply sacrificing the image quality in order to shorten the communication time, the transmission can be performed while taking a trade-off between the image quality of the transmission image and the communication time.

Further, the present invention is characterized in that the compression ratio can be selected by an operator or automatically selected by an apparatus.

According to the present invention, by allowing the operator to select the compression ratio, the operator can select whether to prioritize image quality or communication time. Also, by automatic selection by the device,
The optimal compression ratio is automatically selected.

Further, in the invention, it is preferable that the image input device is an electronic still camera.

According to the present invention, since the image input device is an electronic still camera, the JPEG compression ratio can be easily set in advance from the amount of image data of the electronic still camera.

Further, the present invention is characterized in that the input of image data from the image input device to the color facsimile device is input via a serial connection or via a recording medium.

According to the present invention, image data can be input to a color facsimile apparatus via a serial connection with an image input apparatus or via a recording medium.

Further, the present invention is characterized in that there is provided means for color-converting the color space unique to the image input device into a color space unique to a color facsimile device.

In a general color facsimile apparatus, JPEG is used as a standard encoding method of an input image. However, other applications such as electronic still cameras, personal computers, and the Internet use R (Red) G (Gree
n) Color space YCrCb capable of linear conversion from B (Blue)
Is used, whereas the color facsimile apparatus uses the color space CIELAB. Here, the color space will be described. For example, in a color copying apparatus, since the combination of a scanner and a printer is uniquely determined, in order to make the colors of a document and a copy close to each other, it is necessary to change from RGB, which depends on those characteristics, to C (Cyan) M (Magenta) Y (Y
ellow) It is only necessary to convert K (Black).
However, in color facsimile apparatuses, since the characteristics of input / output devices differ depending on the system, it was expected that the RGB values of the scanner output of a certain system would be directly transmitted to another system, that is, a facsimile apparatus on the receiving side and printed. It is rarely reproduced in color. Therefore, in order to consider color management between different systems, it is necessary to exchange data in a device-independent color space. CIELAB is one of the device-independent color spaces. CIELAB
Is a psychophysical quantity that is determined by the International Commission on Illumination (CIE) and corresponds to the color perceived by the human eye itself and can be measured by a measuring instrument. Also, CIELAB
Is called a uniform color space, and is designed so that the difference in distance between any two points in the space is proportional to the difference in perceived color as much as possible. CIELAB has been adopted as a standard color space for images transmitted and received by a color facsimile apparatus, because of the device-independent properties and the good compression rate of image compression due to the above-described properties.

According to the present invention, for example, when the image input device is an electronic still camera, color conversion of an image expressed in the unique color space YCrCb of the electronic still camera into the unique color space CIELAB of the color facsimile apparatus. Thus, an image with good reproducibility can be transmitted by the transmission partner device.

Further, the invention is characterized in that it comprises a color correcting means for performing a color correction on the color image input from the image input device.

According to the present invention, an image input from the image input device can be subjected to color correction by the color correction means, so that an image of better color reproducibility can be transmitted by the transmission partner device.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a case where image data is input from an electronic still camera (hereinafter referred to as a digital camera) as an image input device to a color facsimile apparatus 1 of the present embodiment and transmitted by facsimile. FIG. 3 is a diagram illustrating an outline of a flow of image processing. In the color facsimile apparatus 1 for encoding and transmitting data of a digital camera as an input image and transmitting the data, the color space YCrCb of the digital camera is converted to the standard color space C of the color facsimile apparatus.
It is necessary to convert to IELAB. For this purpose, the JPEG data of the digital camera is temporarily decoded (step S101), and then the color space YCrCb is converted to the color space CI.
The color conversion to ELAB is performed (step S102). At this time, appropriate color correction is performed (step S103).
Then, the data color-converted into the color space CIELAB is
PEG encoding (step S104), and transmission via a communication line.

FIG. 2 shows the flow of JPEG decoding and encoding processing when image data (hereinafter referred to as digital camera data) 201 of a digital camera is transmitted by the color facsimile apparatus 1. First, a decoding process of the digital camera data 201 for color-converting a color space unique to a digital camera into a color space unique to a color facsimile apparatus will be described. First, the JPEG control code unique to the digital camera is removed from the JPEG file of the digital camera data 201 (202). Also,
At the same time, the file-specific Huffman table 204 and quantization table 206 are extracted. Next, Huffman decoding 2 is performed using the extracted Huffman table 204.
03, and inverse quantization 205 is performed by the quantization table 206. Next, inverse DCT (Discrete Cosine)
Transform), the decoded image 208 can be extracted. Next, color conversion and color correction from YCrCb, which is the color space of the digital camera data 201, to CIELAB, which is the color space of the color facsimile apparatus 1, are performed (2).
09).

Next, a description will be given of an encoding process for facsimile transmission of a decoded image decoded by the decoding process and color-converted into a unique color space. In the encoding process, the reverse of the decoding process is basically performed. First, sub-sampling 210 is performed on the decoded image after color conversion and color correction. The sub-sampling is to thin out the color difference resolution while keeping the luminance resolution unchanged by utilizing the fact that the human eye is less sensitive to the change in color difference than the change in spatial brightness.
Since the color facsimile apparatus 1 of the present embodiment performs the sub-sampling 210, the compression ratio of the image data to be transmitted can be changed by preparing a plurality of sampling ratios. Although the sub-sampling can be compressed by this processing alone, there is an advantage that the number of blocks is reduced by the DCT transform described later, so that the amount of calculation is reduced.

Next, a DCT transform 211, which is a kind of orthogonal transform, is performed, and then a quantization 212 is performed using a quantization table 213. The DCT transform is to divide one block image into a plurality of types of basic patterns having different two-dimensional frequency components. More specifically, the basic pattern has the same number of pixels as one block, and the original image has
It is assumed that each basic pattern is weighted and superimposed. At this time, the weighting coefficient of each basic pattern is called a DCT coefficient, and a total of 64 DCT coefficients of 8 × 8 are obtained in one block. In order to reduce the code amount per DCT coefficient, quantization is performed to take a representative value at fixed value intervals, and information is omitted. The interval between the representative values is called a quantization step.

Since the human eye has a lower sensitivity as the frequency is higher, the image is hardly deteriorated even if the portion is roughly quantized. Therefore, even if the DCT coefficient of the high-frequency basic pattern is largely omitted, the image deterioration is hard to be recognized. . A table that associates the quantization steps for each DCT coefficient is called a quantization table, and can be omitted when the frequency is high as described above.
It differs for each T coefficient, and is set such that the higher the DCT coefficient, the larger the quantization step. By using this quantization table, quantization can be performed such that the code amount is greatly reduced at higher frequencies. This quantization table is most related to the compression ratio of the image data to be transmitted.

The color facsimile apparatus 1 of the present embodiment
By preparing a plurality of quantization tables, the compression ratio of image data to be transmitted can be changed in the same manner as the sampling ratio. Here, if a quantization table with a high compression rate is used, the generated JPEG code image 21
7, the communication time is shortened, but the data quality of the data after decryption by the partner machine is deteriorated. Conversely, when a quantization table with a low compression ratio is used, the data amount increases and the communication time increases, but the image quality of the decoded data improves. Subsequently, Huffman encoding 214 is performed by the optimal Huffman table 215, and then a JPEG control code unique to the color facsimile apparatus is added (216), and the created JPEG code image 217 is transmitted via the communication line.

In the JPEG encoding / decoding process of FIG. 2, the same Huffman table and the same quantization table are used for the decoding process and the encoding process, and the same sampling ratio as that of the image to be decoded is used. For example, even if the color space is different, the digital camera data 201 before decoding is
The data amount of the encoded JPEG encoded image 217 is substantially the same, although there is a difference of several percent. Also, the JPEG code generated by utilizing the fact that the compression ratio after JPEG encoding can be adjusted by changing the sampling ratio used in the sub-sampling 210 of the encoding process and the quantization table 213 used in the quantization 212. By controlling the data amount of the coded image 217, it is possible to balance communication time and image quality.

FIG. 3 is a block diagram showing a configuration of the color facsimile apparatus 1 of the present embodiment. The facsimile apparatus 1 includes a CPU 301, a ROM 302, a RAM 303,
PCMCIA 304, operation panel 305, circuit control unit 3
06, printer control unit 307, color correction data memory 30
8, a multi-level image encoding / decoding unit 309, a binary image encoding / decoding unit 310, an image storage memory 311 and an image processing unit 312. Further, the image processing unit 320 includes the color correction unit 3
13, first color conversion unit 314 and second color conversion unit 31
5 is included.

CPU 301, ROM 302, RAM 30
3, the PCIICIA 304, the operation panel 305, the line control unit 306, the printer control unit 307, and the color correction data memory 308 are connected by a system bus 316, and the image processing unit 312 and the image storage memory 311 are connected by an image bus 317.
Connected by The multi-level image encoding / decoding unit 309 and the binary image encoding / decoding unit 310 are connected to the system bus 3
16 and the image bus 317. Also,
The system bus 316 and the image bus 317 are connected to each other.

The CPU 301 is a ROM 30 in which a control program and various constants necessary for its execution are written.
2, and the overall operation of the color facsimile apparatus 1 together with the RAM 303 for reading and writing variables, control flags, and the like necessary for executing the program. The PCMCIA interface 304 controls input and output of data on a recording medium. This PCMCIA interface 304
By connecting a recording medium to the digital camera data 2
01 can be input to the color facsimile machine 1. Alternatively, the digital camera data 201 may be input to the facsimile apparatus 1 by directly serially connecting to the digital camera. The operation panel unit 305 performs various inputs and displays such as selection of a facsimile number when transmitting a facsimile and a compression ratio by an operator. The line control unit 306 is an interface with a communication line. The printer control unit 307 controls a printer.
The color correction data memory 308 stores various tables for performing color correction on the decoded image 208 in FIG.

The image storage memory 311 temporarily stores image data to be transmitted and received by facsimile. Color correction unit 313
Performs various image processing on the multi-valued image. The first color conversion unit 314 converts the color space YCrCb into the color space CIELA.
B, and the second color conversion unit 315 converts the color space Y
Conversion from CrCb to color space CMYK is performed. The multi-level image encoding / decoding section 309 performs JPEG encoding / decoding processing, and the binary image encoding / decoding section 310 performs decoding and encoding of a binary (monochrome) image. The binary image encoding / decoding unit 310 outputs MH (Modifi)
de Huffuman), MR, MMR, JBIG, and other compression methods can be used to transmit and receive images. In the present embodiment, a case will be described where the digital camera data 201 is transmitted by facsimile via the line control unit 306, but the digital camera data 201 input by the PCMCIA control unit 304 is converted to the second color conversion unit 31.
5, and the color correction unit 313 can convert the data into CMYK data, and the printer control unit 307 can cause the printer to print the data.

Hereinafter, an example of a method of setting an encoding compression rate in transmission of the digital camera data 201 by the color facsimile apparatus 1 in the present embodiment will be described.

The system of the color facsimile apparatus 1 has a table such as Table 1 recorded in the RAM 303 in advance. The table of Table 1 includes a row number, a threshold of a file size (data amount of digital camera data), a sampling ratio, and a quantization table. From the file size of the image of the digital camera data 201,
Using the table of Table 1, the sampling ratio and quantization 21 used in the sub-sampling 210 in FIG.
The compression table 213 used in step 2 is determined, and the image is compressed.

[0032]

[Table 1]

In the table of Table 1, the file size of the digital camera data is A <B <C <D <E. Also, the sampling ratio increases as the file size increases (in Table 1, as it moves to the right), that is, the compression ratio increases. The sampling ratio is the luminance L:
Saturation A: Indicates hue B. In subsampling 210,
The resolution of the saturation A and the hue B, which are insensitive to changes compared to the luminance, is thinned out while the resolution of the luminance L that is sensitive to the human eye remains unchanged. Further, the quantization table is also set such that the compression ratio increases as the file size increases (in Table 1, as it goes to the right).

In transmitting the digital camera data 201, first, the PCMCIA interface 304 acquires the file size of the digital camera data 201 and stores it in the RAM 303. After the color conversion and color correction of the data of the decoded image 208, the digital camera data 20 stored at the time of encoding is decoded.
The system determines which sampling ratio and quantization table to use for the file size of 1 using the table in Table 1. For example, if the file size is equal to or larger than Abyte and smaller than Bbyte, the CPU 301 determines the row number 3 based on the table of Table 1, and determines the sampling ratio 1: 1: 1 and the quantization table b from the row number 3, 2 uses a 1: 1: 1 sampling ratio, and the quantization 212 uses a quantization table b. Then, using these parameters (sampling ratio, quantization table), JPE
G-compressed data is transmitted.

As described above, when the system has a small image file size, the compression ratio is reduced to give priority to the image quality of the transmission image, and when the image file size is large, the communication ratio is shortened by increasing the compression ratio. I do. As described above, by adjusting each parameter (sampling ratio, quantization table) of the table in Table 1 according to the file size, the image quality of the transmission image is not sacrificed simply to shorten the communication time. It is possible to transmit while taking a trade-off between image quality and communication time.

Next, a color facsimile apparatus according to another embodiment of the present invention will be described. The color facsimile apparatus of the present embodiment has the same configuration and functions as the color facsimile apparatus 1 of the above embodiment. In the above embodiment, the system automatically determines the compression ratio of the image data based on the table. However, the color facsimile apparatus of the present embodiment allows the operator to balance the image quality of the transmission image and the communication time to some extent. It should be selectable. Here, the operator preliminarily sets a mode 1 in which the compression rate is low and the communication time is long, but the image quality of the transmission image is prioritized. Further, it is assumed that a mode 3 for balancing the image quality of the transmission image and the communication time can be selected using the operation panel.

In the mode 1, the sampling ratio and the quantization table corresponding to the row numbers 1, 2, and 3 in the table of Table 1 are used. That is, if the file size of the image to be transmitted is smaller than Abyte, the row number 1 is determined by the CPU 301 based on the table, and from this row number 3, the sampling ratio 1: 1: 1 and the quantization table a The file size of the image used by the sampling 210 and the quantization 212 and similarly transmitted is Aby.
If te or more and less than Bbyte, the sampling ratio is 1:
1: 1 and the quantization table b are used, and similarly, if the file size of the image to be transmitted is equal to or greater than Bbyte, the sampling ratio 4: 2: 2 and the quantization table c are used. As described above, in the mode 1, the file size of the image to be transmitted is increased and the communication time is increased, but the image quality of the transmitted image is improved.

Similarly, in mode 2, the sampling ratios and quantization tables corresponding to the row numbers 4, 5, and 6 in the table of Table 1 are used. However, if the file size of the image to be transmitted is smaller than Dbyte, the sampling ratio 4: 2: 2 and the quantization table d are all used. As described above, in mode 2, the size of the image to be transmitted is reduced as a whole, and the image quality of the transmitted image is degraded, but the communication time is reduced.

Further, in the mode 3, the sampling ratio and the quantization table corresponding to the row numbers 2, 3, 4, and 5 in the table of Table 1 are used. However, if the file size of the image to be transmitted is less than Bbyte, the sampling ratio 1: 1: 1 and the quantization table b are used, and if the file size of the image to be transmitted is Dbyte or more, the sampling ratio 4: A 1: 1 and quantization table e is used. In this way, the communication time and the image quality of the transmission image can be balanced.

As described above, the parameters determined by the mode selected by the operator are used when encoding an image, thereby enabling the operator to select a trade-off ratio between communication time and image quality to some extent. .

[0041]

As described above, according to the present invention, the data amount of an image input from an image input device is stored, and the compression rate of the image is determined based on the data amount of the image at the time of encoding. . In other words, if the amount of image data is small, the compression rate is reduced and the quality of the transmitted image is prioritized.If the amount of image data is large, the compression ratio is increased and the communication time is shortened. Instead of sacrificing image quality, transmission can be performed while taking a trade-off between the image quality of the transmission image and the communication time.

Further, according to the present invention, since the compression ratio of the image to be transmitted can be selected by the operator, the operator can select whether to give priority to the image or the communication time. Also, since it is automatically selected by the device,
The optimal compression ratio is automatically selected.

According to the present invention, since the image input device is an electronic still camera, the JPEG compression ratio can be easily set in advance from the amount of image data.

According to the present invention, image data can be input to the color facsimile apparatus via a serial connection with an image input apparatus or via a recording medium.

According to the present invention, an image expressed in a unique color space of an image input device is color-converted into a unique color space of a color facsimile device, so that an image with good reproducibility can be obtained in a transmission partner device. Can be sent.

According to the present invention, color correction can be performed on an image input from the image input device by the color correction means, so that an image having better color reproducibility can be transmitted by the transmission partner device. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a procedure for transmitting digital camera data in a color facsimile apparatus 1 according to an embodiment of the present invention.

FIG. 2 is a diagram showing an encoding / decoding process for transmitting digital camera data in the color facsimile apparatus 1 of FIG. 1;

FIG. 3 is a block diagram showing a configuration of the color facsimile apparatus 1 of FIG.

[Explanation of symbols]

 301 CPU 302 ROM 303 RAM 304 PCMCIA 308 Color correction data memory 309 Multi-level image encoding / decoding unit 313 Color correction unit 314 First color conversion unit 315 Second color conversion unit 316 System bus 317 Image bus

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C077 LL18 LL19 MP08 PP31 PP32 PP33 PP36 PP37 PP49 PP61 PQ08 RR21 SS05 TT09 5C078 AA09 BA57 CA02 DA01 DA02 DB07 5C079 HA01 HB01 HB03 HB08 HB12 LA27 LA31 LB02 NA03 NA18

Claims (6)

[Claims] 1. A color facsimile apparatus for compressing a color image input from an image input device and transmitting the compressed color image to a partner device via a communication line, wherein: an obtaining means for obtaining a data amount of the color image; And a compression ratio selecting means for selecting a compression ratio based on the data amount of the color facsimile. 2. The color facsimile apparatus according to claim 1, wherein said compression ratio is selectable by an operator or automatically selected by an apparatus. 3. The color facsimile apparatus according to claim 1, wherein said image input device is an electronic still camera. 4. The color image processing apparatus according to claim 3, wherein the input of image data from the image input device to the color facsimile device is input via a serial connection or via a recording medium. Facsimile machine. 5. A color facsimile apparatus according to claim 3, further comprising means for converting a color space unique to said image input apparatus into a color space unique to a color facsimile apparatus. 6. A color facsimile apparatus according to claim 3, further comprising a color correction means for performing color correction on a color image input from said image input device.