Image processing apparatus and method

Abstract: It is a concern of the invention to minimize an image deterioration due to an image conversion. For such an object, among parameters regarding a picture quality of a color facsimile apparatus on the transmission side, color image information is encoded in accordance with a parameter which optimizes the picture quality and stored. A parameter regarding the picture quality of the color image information which a color facsimile apparatus on the reception side has is recognized and compared with the parameter of the color facsimile apparatus on the transmission side. In accordance with the comparison result, an image conversion of the stored color image information is executed.

Description: BACKGROUND OF THE INVENTION Field of the Invention The invention relates to image processing apparatus and method which can perform a color image communication. Related Background Art Hitherto, in a color facsimile apparatus which can perform a color image communication, in case of using preset resolution and paper size and, further, a JPEG encoding, a document is encoded and stored in accordance with a sub-sampling ratio, a quantization table, a color space, an interleave format, and parameters of a Huffman table and is transmitted. However, in case of the above conventional color facsimile apparatus, since the reception side doesn't consider an ability to reproduce a good picture quality, vain image data is transmitted to the reception side or an image transmission in which a reproducing ability on the reception side is not most effectively used is executed. SUMMARY OF THE INVENTION It is a concern of the invention to provide a color image processing apparatus in which the transmission side doesn't have characteristics which are matched with characteristics of a document stored on the reception side, and even in case of image converting the document and transmitting, a deterioration of the image due to such an image conversion can be minimized. Japanese Patent Specification No JP 06105163 discloses a picture transmission system which sets the data quantity of picture information to be transmitted in response to the idle capacity of the data storage means at a reception side. By preparing plural quantization tables for encoding the picture data and in response to an experimental test step the combination between the quantization tables and scale factors can be set at the transmission side. Japanese Patent Specification No JP 05219332 discloses an arrangement which enables a transmission side to send a picture in a mode designated by a function parameter by sending the function parameter. The function parameter can be, for example, picture quality, size and resolution of a picture required by a receiver side. According to aspects of the invention there is provided a colour image processing apparatus as set out in claim 1 and a method of processing colour image data as set out in claim 8. Other features of the present invention will become apparent from the following detailed description which is given by way of example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing a construction of a color facsimile apparatus according to an embodiment of the invention; Fig. 2 is a flowchart showing a storing processing sequence of a transmission document in the facsimile apparatus according to the embodiment; Fig. 3 is a diagram showing an image selection table according to the embodiment; Fig. 4 is a diagram showing a quantization table according to the embodiment; Fig. 5 is a flowchart showing a transmission sequence of a storing document in the facsimile apparatus according to the embodiment; Fig. 6 is comprised of Fig. 6A and Fig. 6B showing flowcharts illustrating a transmission sequence of a storing document in the facsimile apparatus according to the embodiment; Fig. 7 is a flowchart showing a transmission sequence of a storing document in the facsimile apparatus according to the embodiment; Fig. 8 is a diagram showing an image conversion table which is set in the embodiment; Fig. 9 is a flowchart showing a sequence when a transmission document is stored in the facsimile apparatus according to a modification; Fig. 10 is a flowchart showing a transmission sequence of a storing document in the facsimile apparatus according to the modification; Fig. 11 is comprised of Fig. 11A and Fig. 11B showing flowcharts illustrating a transmission sequence of a storing document in the facsimile apparatus according to the modification; and Fig. 12 is a flowchart showing a transmission sequence of a storing document in the facsimile apparatus according to the modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment according to the present invention will now be described in detail hereinbelow with reference to the drawings. Fig. 1 is a block diagram showing a construction of a color facsimile apparatus (hereinafter, simply referred to as a facsimile apparatus) according to the embodiment of the invention. The facsimile apparatus according to the embodiment is connected to an ISDN (Integrated services digital network). In Fig. 1, reference numeral 1 denotes a scanner which functions as a device to read a color original; 2 a gamma conversion unit for converting a density characteristic of image data read by the scanner 1; and 3 a pixel density conversion unit for performing a resolution conversion of the image, a zooming process, or the like. Reference numeral 4 denotes an RGB/YUV conversion unit for converting an RGB image read by the scanner 1 to a YUV image that is optimum to an ADCT (adaptive discrete cosine transform). Reference numeral 5 denotes a sub-sampling unit which is a circuit to drop resolutions of U and V components which are not visually sensitive while keeping a resolution of a Y component that is visually sensitive. Reference numeral 6 denotes a DCT (discrete cosine transform) unit for converting block components of (8 x 8) pixels to (8 x 8) frequency components. Reference numeral 7 denotes a quantization unit for quantizing (dividing) an arithmetic operation result of the DCT by a table designated from among a plurality of quantization tables. Reference numeral 8 denotes a Huffman encode unit. As a result of the quantization in the quantization unit 7, since many results of 0 excluding a DC component and a low frequency component are obtained, a Huffman encoding is performed by using the number of continuous 0 values. Reference numeral 9 denotes a lookup table for quantization which is used in the quantization unit 7 and an inverse quantization unit 15. In the embodiment, as a quantization table that is used at the time of an inverse quantization upon reception, a quantization table of the same table number as that of the table used in the quantization on the transmission side is downloaded from the quantization table 9 and is used. Reference numeral 10 denotes a lookup table which is used in the Huffman encode unit 8 and a Huffman decode unit 14. In the embodiment, as a table which is used at the time of a Huffman decoding upon reception, the same table as the table used in the Huffman encoding on the transmission side is downloaded from the Huffman table and is used. Reference numeral 11 denotes a hard disk to store a storing document and a reception document and 12 indicates a buffer for transmitting and receiving image data between a CCU (communication control unit) 13 and the hard disk 11 at an optimum speed. The CCU 13 controls call generation and reception to/from a terminal on the reception side and transmission and reception of image data by using a predetermined communication protocol. The Huffman decode unit 14 decodes the Huffman encoded data. The inverse quantization unit 15 inversely quantizes the quantized data by using the foregoing quantization table. Reference numeral 16 denotes an inverse DCT (inverse discrete cosine transform) unit for converting the (8 x 8) frequency components which were DCT converted by the DCT unit 6 to the data of (8 x 8) pixel blocks. Reference numeral 17 denotes an interpolation processing unit. In the case where resolutions of the U and V components are reduced as compared with a resolution of the Y component by a sub-sampling process at the time of the storage of the document, the interpolation processing unit 17 interpolates such a reduced resolution. Reference numeral 18 denotes a YUV/RGB conversion unit for converting the image data of YUV to a color space of RGB; 19 a pixel density conversion unit for perform a resolution conversion, a zooming process, or the like of an image; and 20 a printer which can color output the image data at a high resolution of 400 dpi. Fig. 2 is a flowchart showing a processing sequence when the facsimile apparatus of the embodiment actually stores a transmission document. First in step S1 in Fig. 2, the user selects a paper size, a resolution, a sub-sampling ratio between a luminance component and a chromaticity component, a quantization table, and the like by a console unit of the facsimile apparatus. (In the embodiment, the sub-sampling ratio denotes a ratio between a sampling frequency of the luminance component and a sampling frequency of two chromaticity components.) In step S2, the items selected in step S1 and, further, a color space, an interleave format, and a Huffman table specified suggestively in the system are written into an image selection table shown in Fig. 3. In step S3, they are stored by using a quantization table of the parameters such that a color image which has been preset in the facsimile apparatus of the embodiment can be stored at a high picture quality, in the embodiment, the parameters such that the preset color image can be stored most in detail, namely, a resolution of 400 dpi, a sub-sampling ratio of 1 : 1 : 1, and a compression ratio is smallest. Namely, those items are quantized by a quantization table of a lowest compression ratio by using a sub-sampling ratio such that the resolution is highest and the best color is derived and are stored. Fig. 3 shows the image selection table set in step S2 in Fig. 2. A parameter of the paper size selected from the paper sizes of B5, B4, A4, and A3 held in the facsimile apparatus is set in F1 in Fig. 3. A parameter of the resolution selected from the resolutions of 400 dpi, 300 dpi, and 200 dpi held in the facsimile apparatus is set in F2. A parameter selected from the sub-sampling ratios of (1 : 1 : 1), (2 : 1 : 1), and (4 : 1 : 1) held in the facsimile apparatus is set in F3. Further, a table number selected from quantization tables shown in Fig. 4 and a kind indicating whether the selected table is default or not are set in F4, respectively. Values of YUV set so as to be used in the system among parameters allocated to each of color spaces YUV, RGB, La*b* held in the facsimile apparatus are set in F5. Block-sequential values set so as to be used in the system among parameters allocated to each of block-sequence and block-area-sequence of the interleave formats held in the facsimile apparatus are set in F6. A kind of table selected from Huffman tables held in the facsimile apparatus and a kind indicating whether the selected Huffman table is default or not are set in F7, respectively. Fig. 4 shows quantization tables of the embodiment. The parameters of the quantization table to be set in F4 in Fig. 3 are stored in such quantization tables. In the embodiment, values such that image data is compressed at high picture qualities in accordance with the order from F11, F12, and F13 are set in the quantization tables shown in Fig. 4 (compression ratios deteriorate in accordance with this order). Namely, values of matrices decrease in accordance with the order of F11, F12, and F13. F11 relates to a default quantization table and the other tables are unique to the facsimile apparatus. Figs. 5 to 7 are flowcharts showing a transmission sequence of a storing document in the facsimile apparatus of the embodiment. In step S101 in Fig. 5, the facsimile apparatus connects a transport layer and the following. That is, layers from 2 to 4 of an OSI reference protocol are connected by the CCU 13 in Fig. 1. Processes in step S2 and subsequent steps, which will be explained hereinlater, conform with a practical application example of a communication protocol defined by the recommendation T.62 of ITU-T (International Telecommunication Union - Telecommunication recommendation). In step S102, a command of session start (hereinafter, abbreviated to as CSS) is generated to the reception side. In step S103, when a response of session start positive (hereinafter, abbreviated to as RSSP) from the reception side is received, document characteristics (a paper size, an interleave format, a sub-sampling ratio, whether the quantization table is default or not, a kind indicating whether the table is downloaded to a partner's apparatus or not, whether the Huffman table is default or not, a kind indicating whether the table is downloaded to the partner's apparatus or not, an image transfer density, a color space) which can be set in the own terminal are transmitted to the reception side by document program file attributes which are described in session user data (hereinafter, abbreviated to SUD) of a command of document function list (hereinafter, abbreviated to CDCL) in step S104. In step S105, judging processes in the following steps S106 to S112 are performed by the SUD in a response of document function list positive (hereinafter, abbreviated to RDCLP) sent from the reception side. Namely, in step S106, the AND of document characteristics in the above image selection table and document characteristics sent from the reception side is calculated. Thus, if it is "true" with respect to all of the document characteristics, the processing routine advances to step S107. If there is a "false" in any one of the documents, the processing routine advances to step S108 (Fig. 6A). In step S107, the image selection table is copied as it is into an image conversion table. In step S108, a check is made to see if the reception side can use the paper size designated on the transmission side or not. When the designated paper size cannot be used, step S109 follows. When the designated paper size can be used, the processing routine advances to step S110. In step S109, first, when the designated paper size can be changed to a paper size such as letter size, regal size, or the like that is relatively close to the paper size of the A or B series, the designated paper size is converted to such a size. However, when such a size conversion is impossible, the A4 size as a default paper size is set into the image conversion table. In step S110, a check is made to see if the reception side can use the interleave format designated on the transmission side or not. When such a format cannot be used, the processing routine advances to step S111. When it can be used, step S112 follows. Namely, a default interleave format is set into the image conversion table in step S111. In step S112, a check is made to see if the reception side can use the designated sub-sampling ratio or not. When the designated sub-sampling ratio cannot be used, step S113 follows. When it can be used, step S114 follows. Namely, a default sub-sampling ratio is set into the image conversion table in step S113. In step S114, in the case where it is designated such that the reception side downloads the same table as the quantization table used on the transmission side and uses it, if the reception side cannot use such a table, the processing routine advances to step S115. If such a table can be used, step S116 follows. In step S115, a default quantization table is set into the image conversion table. In step S116, in the case where it is designated such that the reception side downloads the Huffman table used on the transmission side and uses it, if the reception side cannot use such a Huffman table, the processing routine advances to step S117. If it can be used, step S118 follows. Namely, in step S117, a default Huffman table is set into the image conversion table. In step S118, a check is made to see if the reception side can use the designated resolution or not. When the resolution cannot be used, the processing routine advances to step S119. If it can be used, step S120 follows. In step S119, a resolution whose level is lower than the designated resolution by one level among the resolutions held on the reception side is set into the image conversion table. In step S120, a check is made to see if the reception side can use the designated color space or not. When the reception side cannot use the designated resolution, the processing routine advances to step S121. When it can be used, step S122 follows. Namely, in step S121, a color space which the reception side has or a default color space is set into the image conversion table. In step S122, the image conversion is executed in accordance with the image conversion table set in steps S108 to S121 mentioned above. Namely, the document data stored in the hard disk 11 is decoded by an almost same procedure as that in case of decoding the reception document. A method of the image converting process in step S122 in the embodiment will now be described. When the image conversion is performed, as a Huffman table that is used in the Huffman decode unit 14 shown in Fig. 1 and a quantization table which is used in the inverse quantization unit 15, the same Huffman table and quantization table as those used upon storage are used. After that, the (8 x 8) frequency components which were DCT converted upon storage are converted to the (8 x 8) pixel block data by the IDCT unit 16. The interpolation processing unit 17 executes an interpolating process for the sub-sampling executed upon storage. Further, after the YUV/RGB conversion unit 18 was YUV/RGB converted, the process in the pixel density conversion unit 19 is not executed but the process in the pixel density conversion unit 3 is performed. The paper size and resolution are converted in accordance with an image conversion table shown in Fig. 8. After the color space conversion was performed by the RGB/YUV conversion unit 4, a sub-sampling according to the image conversion table shown in Fig. 8 is executed by the sub-sampling unit 5. After the DCT conversion was performed by the DCT unit 6, the data is quantized by the quantization unit 7 by using the quantization table of the image conversion table shown in Fig. 8. Finally, the data is encoded by the Huffman encode unit 8 by using the Huffman table in the image conversion table shown in Fig. 8. The encoded data is stored in the hard disk 11. On the other hand, in step S123 in Fig. 7, a document profile to be actually sent, namely, in the case where the image conversion was performed, the parameter set in the conversion table or, in the case where a default document profile is used, its parameter is sent to the SUD in a command of document start (hereinafter, abbreviated to CDS), namely, a command indicative of the start of the document and the start of the first page on the reception side. In steps S124 and S125, the document data is transferred by a plurality of commands of document user information (hereinafter, abbreviated to CDUI). In step S126, a command of document end (hereinafter, abbreviated to CDE) is used to indicate the end of document, further, a final check point. In step S127, a positive confirmation for the final check point is given to a response of document end positive (hereinafter, abbreviated to RDEP). In step S128, a command of session end (hereinafter, abbreviated to CSE) is used to normally finish the session. Further in step S129, a fact that a terminal to be called normally finished the session is shown to a terminal on the transmission side by a response of session end positive (hereinafter, abbreviated to RSEP). In step S130, a transport layer and the following are disconnected and the transmission is finished. Fig. 8 shows the image conversion table set in steps S109 to S121 shown in Figs. 6A and 6B. A parameter of the paper size is set in F21. A parameter of the resolution is set in F22. A parameter selected from the sub-sampling ratios is set in F23. The table number selected from the quantization table F4 shown in Fig. 3 and a kind indicating whether it is a default or not are set in F24, respectively. Values of parameters allocated to the color spaces YUV, RGB, and La*b*, respectively, are set in F25. Parameter values allocated respectively to the block-sequence and area-sequence of the interleave formats held in the facsimile apparatus according to the embodiment are set in F26. A kind of Huffman table and a kind indicating whether it is a default or not are set in F27, respectively. According to the embodiment described above, the transmission document is stored on the transmission side by using the resolution, sub-sampling ratio, and quantization parameter at which the image can be stored at a preset high picture quality and which the facsimile apparatus on the transmission side has. The image conversion of the stored document is performed in accordance with the comparison result of those parameters and the parameters which the facsimile apparatus on the reception side has and the converted image is transmitted. Thus, even in the case where the reception side doesn't have the characteristics of the document stored on the transmission side and performs the image conversion and transmits the converted image, an image deterioration by the image conversion can be minimized. The same parameters as those in the image selection table that is set in step S2 can be also used as read parameters upon storage in step S3 in the embodiment. In such a case, when the document characteristics designated in step S106 in Fig. 5 are included on the reception side, the image data stored in the hard disk 11 is transmitted as it is. Therefore, since a troublesomeness for decoding the stored image data and again storing it are eliminated, the image can be smoothly transmitted. <Modification> A modification of the above embodiment will now be described hereinbelow. Fig. 9 is a flowchart showing a sequence upon storage of a transmission document in the facsimile apparatus according to a modification of the above embodiment. In step S11 in Fig. 9, a paper size, a resolution, a sub-sampling ratio, a quantization table, and the like are selected by a console unit of the facsimile apparatus. In step S12, the items selected in step S11, and further, a color space, an interleave format, and a Huffman table which were suggestively specified in the system are written in the image selection table in Fig. 3 in a manner similar to the above embodiment. In step S13, a default value of document characteristics to be transmitted and received in the session user data (SUD) and the value written in the above image selection table are compared. When they are equal, a document storage is executed in accordance with the parameters written in the image selection table in step S14. In step S13, however, when it is judged that the default value of the SUD and the value in the image selection table differ, the document is stored by using the parameters at which the image data can be stored at a preset high picture quality by the facsimile apparatus of the modification, namely, by using the quantization table of the resolution of 400 dpi, sub-sampling ratio of 1 : 1 : 1 and the lowest compression ratio. A transmission sequence of the storing document in the facsimile apparatus according to the modification will now be described. Figs. 10 to 12 are flowcharts showing the transmission sequence of the storing document in the facsimile apparatus according to the modification. In steps S201 to S205 in Fig. 10, processes similar to those in steps S101 to S105 according to the embodiment shown in Fig. 5, namely, a negotiation with a partner side by a communication is executed. In step S206, a check is made to see if the resolution, sub-sampling ratio, quantization table, color space, interleave format, and Huffman table shown by the designated parameters coincide with the default values of the document file which are defined in the ITU-T or not. When they coincide, those parameters are stored as they are and processes in step S224 and subsequent steps shown in Fig. 12 are executed. However, when both of the parameters don't coincide, in step S207, the AND of the document characteristics in the image selection table and the document characteristics sent from the reception side is calculated in a manner similar to the foregoing embodiment. With respect to all of the document characteristics, when they are "true", the processing routine advances to step S208. When any one of the document characteristics is "false", the processing routine advances to step S209 and subsequent steps shown in Figs. 11A and 11B. A processing procedure shown in steps S209 to S223 in Figs. 11A and 11B in the modification are similar to the processes regarding the above embodiment, namely, the processing procedure shown in steps S108 to S122 in Figs. 6A and 6B. Processes in steps S224 to S231 shown in Fig. 12 are also similar to the processes regarding the embodiment shown in Fig. 7. Therefore, their descriptions are omitted here. As mentioned above, according to the modification, when the instructed parameters coincide with the default values defined by the ITU-T, the transmission document is stored as it is and, after that, it is transmitted. In the other cases, in the facsimile apparatus, the document is stored by using the parameters at which the image data can be stored at the preset high picture quality irrespective of the parameters designated by the operator. The image stored is converted in accordance with parameters which are closest to the parameters instructed on the transmission side among the abilities which the facsimile apparatus on the reception side has. Thus, the image conversion that is perfectly matched with the ability on the reception side can be performed. The image deterioration in association with the image conversion can be minimized. In the above embodiment and modification, an example of the color facsimile apparatus by the ADCT type of what is called a JPEG has been shown and described. The invention, however, is not limited to such an example but can be also applied to a color facsimile apparatus of a dynamic arithmetic operation encoding type of a JBIG. In such a case, a color facsimile apparatus having a similar effect can be provided by an almost similar sequence except that encoding methods of them merely differ although no quantization table exists. The invention can be applied to a system constructed by a plurality of equipment or an apparatus constructed by one equipment. The invention can be also applied to a case where the invention is accomplished by supplying a program to a system or an apparatus. As described above, according to the invention, even in the case where the reception side doesn't have the characteristics of the document stored on the transmission side but performs the image conversion and transmits the converted image data, the image deterioration due to the image conversion can be also minimized. Even in the case where the reception side doesn't have the characteristics of the document stored on the transmission side, the reception side performs the image conversion that is perfectly matched with the ability on the reception side and transmits the converted image data, so that the image deterioration due to the image conversion can be minimized.

Claims: A color image processing apparatus which communicates color image information comprising: encoding means (8) for quantizing colour information on the basis of a predetermined quantization table (9) and encoding the quantized information; converting means (15) for converting the image encoded by said encoding means to encoded image information quantized by a second quantization table different from said first predetermined quantization table, said second quantization table being one which is available to a reception side to which the encoded information is to be transmitted; and transmitting means (13) for transmitting the coded image information output by said converting means to said reception side. Apparatus according to claim 1, wherein said converting means are adapted to convert the picture quality of the color image information. Apparatus according to claim 1 or claim 2, wherein the converting means is adapted to convert the picture quality in response to a parameter which is based on information received from the reception side. Apparatus according to claim 3, wherein the encoding by said encoding means includes irreversible encoding. Apparatus according to any one of the preceding claims and comprising: transforming means for performing an orthogonal transformation of image information; said encoding means being adapted to quantize the orthogonal transformed image using said first predetermined quantization table. Apparatus according to claim 5, wherein said converting means are adapted to use the lowest compression ratio as a first quantization parameter. A method of a color image processing comprising: a step of quantizing colour information on the basis of a predetermined quantization table and encoding the quantized information; a step of converting the image encoded by said encoding means to encoded image information quantized by a second quantization table different from said first predetermined quantization table said second quantization table being one which is available to a reception side to which the encoded information is transmitted; and a step of transmitting the coded image information output by said converting means to said reception side. A method according to claim 7, wherein said converting means are adapted to convert the picture quality of the color image information. A method according to claim 7 or claim 8, wherein the converting step converts the picture quality in response to a parameter based on information received from the reception side. A method according to claim 9, wherein the encoding step includes irreversible encoding. A method according to any one of claims 8 to 10 and comprising: performing an orthogonal transformation on the colour image information prior to encoding. A method according to claim 11, wherein said converting step uses the lowest compression ratio as a first quantization parameter.

Inventors: KOSAKA MASAHIKO, KOSAKA, MASAHIKO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: H04N1
IPC codes: H04N1