JP2005086543A - Image reading method, image reader, program, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of selecting an optimal reading rate when a final image is read out. <P>SOLUTION: The image reader comprises a circuit 104 for compression encoding image data, a CPU 107 for estimating a compression rate at the time of regular image reading from the compression rate of preliminary scanning image, and a CPU 107 for selecting a reading rate optimal to a reading document image from a compression rate estimated by the CPU 107 and a practical transfer rate of an interface circuit 105. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image reading method, an image reading apparatus, a program, and a storage medium.

  In general, in an image reading apparatus, the quality of a read image is improved, and as a result, higher definition and higher gradation are being promoted. That is, in order to read finer image information of a document image than a conventional image reading apparatus, the resolution is improved by means such as increasing the number of pixels of a photoelectric conversion element such as a CCD (for example, Patent Document 1).

  Further, the density reproducibility of the document image is improved by increasing the number of output bits of the A / D converter for converting the analog signal output from the photoelectric conversion element into a digital signal.

  Along with the improvement of the reading image quality, image data sent from the image reading apparatus to a host device serving as an information processing apparatus such as a personal computer (personal computer) increases, and therefore the image reading time is prolonged.

  On the other hand, in order to improve the convenience of the image reading apparatus, an increase in reading speed is also required.

  To meet these goals of increasing the resolution of reading, increasing image data due to improved density reproducibility by increasing input / output gradation, and shortening the time required to read images to improve work productivity and convenience In some cases, an interface used for image data communication does not necessarily have a sufficient data transfer speed, and a lack of bandwidth in image data transmission may impede reading capability.

  In order to achieve these two contradictory purposes, image data sent by the image reading apparatus as described above is also compression-encoded and transmitted to the host apparatus (see, for example, Patent Documents 2 and 3). ).

  In the field of data compression technology, many different data compression methods exist in the past. The compression methods can be roughly classified into two categories: lossy compression coding and lossless compression coding.

  Lossy compression coding is coding that results in loss of information and thus does not compensate for the complete reproduction of the original data. The goal of such lossy compression coding is to prevent the change from being uncomfortable or noticeable even if it changes from the original data.

  In lossless compression coding, all the information is preserved and the data is compressed in a way that allows complete restoration. Lossless compression coding is also called lossless compression because it can be accurately restored without losing information of the original data. In lossless compression encoding, density data of a document image is converted into an output codeword. If the compression processing unit operates satisfactorily, the code word is expressed with a bit number smaller than the bit number required for the input symbol (original image density data) before encoding. Non-lossy compression coding methods include a dictionary compression coding method (for example, Lempel-Ziv method), a run length compression coding method, a count compression coding method, an entropy compression coding method, and the like. In a lossless image compression coding scheme, compression is based on prediction or context and coding.

  For example, the JBIG standard for facsimile compression and DPCM (differential pulse code modulation—option of JPEG standard) for continuous tone images can be cited as lossless compression encoding processes for images.

  In the lossy compression coding system, density data of an input symbol or a document image is quantized and converted to an output codeword. Quantization aims to remove important feature quantities of data while preserving important feature quantities of data.

  Lossy compression coding systems often use transforms to concentrate energy prior to quantization. An example of the lossy compression encoding method for image data is the JPRG method.

In recent image reading apparatuses, for the purpose of improving the color reproducibility of an original image, not only the hardware mechanism of the image reading apparatus but also a host apparatus side is responsible for a lot of image processing. For this reason, the lossless compression coding method is used among the above compression methods because it is necessary to prevent the image quality to be deteriorated due to the compression on the image to be processed on the host device side. .
JP 2000-115491 A Japanese Patent Laid-Open No. 7-58945 JP-A-9-55832

  However, in the configuration in which the lossless compression encoding method is used as the compression encoding method of the image reading apparatus as in the above-described conventional example, the characteristic of the original image to be read is reflected in the encoding efficiency. In addition to the fact that the amount of compressed data does not become constant, there is a problem that a high compression rate cannot be achieved depending on the original image and the encoding parameter.

  In addition, even if the reading resolution is the same, the amount of compressed data does not become constant depending on the original image to be read, so the average compression rate in a general original image is obtained by a statistical method, The reading speed, that is, the image data generation speed is determined based on the compression rate.

  As described above, since a fixed value statistically determined regardless of the document is used as the predicted compression rate, when the document image is complicated, the reading speed relative to the compression rate, that is, the reading optical system When the moving speed is too fast, the reading mechanism often needs to be paused, which may result in image quality degradation due to mechanical vibrations and waste of reading time due to time loss when restarting after releasing the pause. It was.

  Even if the original image contains few characters and designs, the transmission bandwidth of the interface can be used up in order to perform a reading operation at a predetermined reading speed regardless of the original image. There wasn't.

  Therefore, an object of the present invention is to provide an image reading method, an image reading apparatus, a program, and a storage medium that can select an optimum reading speed at the time of reading a final image.

  Another object of the present invention is to provide an image reading method, an image reading apparatus, a program, and a storage medium capable of selecting a reading speed that fully utilizes the function of the image data transmission buffer memory.

  In order to achieve the above object, the image reading method of the present invention converts the density information of the read original into an electrical signal by the photoelectric conversion element, and moves the original or the reading optical system in a direction perpendicular to the arrangement direction of the photoelectric conversion elements. In the image reading method of reading an image on a document by moving to the compression encoding step of compressing and encoding image data, and compression for estimating the compression rate at the time of reading the main image from the compression rate of the pre-scanned image A rate estimation step, and a reading speed selection step of selecting an optimum reading speed for the read document image from the compression rate estimated by the compression rate estimation step and the execution transfer speed of the interface.

  In order to achieve the above object, according to the image reading method of the present invention, the density information of the read original is converted into an electrical signal by the photoelectric conversion element, and the original or the reading optical system is perpendicular to the arrangement direction of the photoelectric conversion elements. In an image reading method for reading an image on a document by moving in a different direction, a compression encoding step for compressing and encoding image data and a compression rate of image information compressed by the compression encoding step are recorded and stored. Recording step, a compression rate estimation step for estimating a compression rate under different reading conditions from the compression rate recorded and stored by the recording step, an output of the compression rate estimation step, and an execution transfer rate of a given interface And a sub-scanning speed selecting step for selecting an optimum sub-scanning speed.

  In order to achieve the above object, the image reading apparatus of the present invention converts the density information of the read original into an electrical signal by the photoelectric conversion element, and the original or the reading optical system is perpendicular to the arrangement direction of the photoelectric conversion elements. In an image reading apparatus that reads an image on a document by moving the image in a different direction, a compression encoding unit that compresses and encodes image data and a compression rate at the time of reading the main image are estimated from the compression rate of the pre-scanned image And a reading speed selecting means for selecting an optimum reading speed for the read original image from the compression ratio estimated by the compression ratio estimating means and the execution transfer speed of the interface.

  Further, in order to achieve the above object, the image reading apparatus of the present invention converts the density information of the read original into an electrical signal by the photoelectric conversion element, and the original or the reading optical system is perpendicular to the arrangement direction of the photoelectric conversion elements. In an image reading apparatus that reads an image on a document by moving in a different direction, a compression encoding unit that compresses and encodes image data, and a compression rate of image information compressed by the compression encoding unit are recorded and stored Based on the output of the compression ratio estimation means and the execution transfer rate of a given interface, the recording means for recording, the compression ratio estimating means for estimating the compression ratio under different reading conditions from the compression ratio recorded and stored by the recording means, And a sub-scanning speed selecting means for selecting an optimum sub-scanning speed.

  According to the present invention, it is possible to select an optimum reading speed at the time of reading a final image.

  Further, according to the present invention, it is possible to select a reading speed that fully utilizes the function of the image data transmission buffer memory.

  Embodiments of an image reading method, an image reading apparatus, a program, and a storage medium according to the present invention will be described with reference to the drawings.

[First Embodiment]
First, a first embodiment of the present invention will be described with reference to FIGS.

  The image reading apparatus according to the present embodiment has a function of predicting the amount of compressed data that matches the document content by estimating the compression rate of the document image based on the preview image read at a low resolution. To do.

  FIG. 1 is a block diagram showing a configuration of an information processing system having an image reading apparatus according to the first embodiment.

  In FIG. 1, reference numeral 100 denotes an image reading apparatus according to the present embodiment, which is a line sensor (CCD) 101, an A / D converter 102, an image processing circuit 103, a compression encoding circuit 104, and an interface (I / F) circuit 105. And an image buffer memory 106 and a CPU (Central Processing Unit) 107.

  The line sensor 101 is composed of photoelectric conversion elements arranged on a straight line, and the reflected light of the read original illuminated by an illumination lamp (not shown) is imaged on the line sensor 101 by a reading optical system (not shown). The line sensor 101 converts luminance information into an analog electrical signal. Further, by driving the reading optical system or the document at a constant speed in synchronization with the image reading circuit by a drive system (not shown), the position where the image is formed on the line sensor 101 moves in the sub-scanning direction on the document. To do.

  The A / D converter 102 converts an analog electric signal output from the line sensor 101 into a digital electric signal. The image processing circuit 103 performs various image conversions such as resolution conversion and color correction on the digitized image information. The compression encoding circuit 104 compresses and encodes image data after image processing. The interface circuit 105 transmits the compression-encoded image data to the host information processing apparatus 200 described later via the interface 110, or receives a command from the host information processing apparatus 200 described later. The image buffer memory 106 temporarily stores and stores image data when the image data is input from the compression encoding circuit 104 to the interface circuit 105 beyond the bandwidth of the interface 110. The CPU 107 controls each component of the image reading apparatus 100. A RAM (random access memory) that records and stores the compression rate of each line output from the compression encoding circuit 104, and a control procedure related to the apparatus. A ROM (Read Only Memory) for recording is attached.

  The CPU 107 is optimal for the read original image from the function of the compression rate estimation means for estimating the compression rate at the time of reading the main image from the compression rate of the prescanned image and the estimated compression rate and the execution transfer speed of the interface circuit 105. A function of reading speed selection means for selecting a reading speed is provided. Further, the CPU 107 calculates the execution transfer rate of the interface circuit 105 from the result of communication by the communication unit that performs communication of pseudo image data without the scanning operation between the image reading apparatus 100 and the host information processing apparatus 200. It has the function of. If the estimated compression rate at the time of reading the main image is close to 1 or the data amount is predicted to increase due to the compression encoding process by the compression encoding means, the CPU 107 reads the image at the time of reading the main image. It has a function of a control means for controlling so as not to perform data compression processing. Further, the CPU 107 has a function of document type determination means for determining the document type of the pre-scanned image, and performs control so that the compression process is not performed when the CPU 107 determines that the document is a halftone print document. . Further, when the CPU 107 has a plurality of compression encoding units, it has a function of a compression encoding selection unit that selects and uses one of these compression encoding units, and has the highest compression efficiency for each document type. A compression encoding means is selected. Further, the CPU 107 has a function of sub-scanning speed selection means for selecting an optimum sub-scanning speed based on the output relating to the compression ratio estimation and the execution transfer speed of the given interface circuit 105.

  A host information processing apparatus 200 such as a personal computer (personal computer) has an interface (I / F) circuit 201, a compressed data decoding unit 202, an image storage unit 203, and an image display unit 204.

  The interface circuit 201 transmits a command to the image reading apparatus 100 via the interface 110 or receives compressed and encoded image data. The compressed data decoding unit 202 expands and decodes the compressed encoded image data received from the image reading apparatus 100 via the interface circuit 201. The compressed data decoding unit 202 may be configured by hardware according to the specifications of the host information processing apparatus 200, or may be configured by software executed by a general-purpose CPU (central processing unit) (not shown).

  The image storage unit 203 stores the image data expanded and decoded by the compressed data decoding unit 202, and is configured by a memory, a magnetic recording device, or the like. The image display means 204 displays the image data expanded and decoded by the compressed data decoding means 201, and is constituted by a CRT (cathode ray tube) display device or the like, and displays preview image data and main scan image data. Used for displaying various information related to image reading.

  The image reading apparatus 100 and the host information processing apparatus 200 are communicably connected via an interface communication path 110 to constitute an information processing system.

  FIG. 2 explains the operation of the image reading apparatus 100 according to the present embodiment based on FIG.

  FIG. 2 is a flowchart showing an operation flow of the information processing system having the image reading apparatus 100 according to the present embodiment.

  When the user operates the host information processing apparatus 200 to instruct to read a preview image, the host information processing apparatus 200 that has been in the operation instruction waiting state (step S201) until then has a resolution for reading the preview image, a reading range, and the like. The parameter information is transmitted to the image reading apparatus 100 (step S202). The image reading apparatus 100 that has been in the operation instruction waiting state (step S251) until then receives the preview reading parameter (step S252) through this communication.

  Subsequently, the host information processing apparatus 200 transmits a preview read start command (step S203). Receiving the reading start command (step S253), the image reading apparatus 100 starts the reading operation of the original image, sequentially compresses and encodes the original image data, and transmits it to the host information processing apparatus 200 (step S254). The host information processing device 200 receives the compression-encoded document image data (step S204), and decompresses and restores this data (step S205). This restoration process may be performed in parallel with the reception of the image data, or the expansion and restoration can be performed collectively after reception of all the image data is completed.

  The image reading apparatus 100 that has finished reading the document image in the range specified by the preview reading parameter performs a reading end process (step S255) such as returning the reading mechanism to the initial state, and waits for the next command (step S256). to go into.

  On the other hand, the host information processing apparatus 200 that has received the compressed image data (step S204) and decompressed and restored (step S205) displays a preview image on the image display means 204 (see FIG. 1). Step S206).

  Based on the preview image displayed on the image display unit 204, the host information processing apparatus 200 processes designation of image reading parameters such as the image reading range on the original and the reading resolution (Ndpi) of the main scan instructed by the user ( In step S207, a main scan start request for reading an image to be finally stored is awaited (step S208).

Receiving the main scan start request, the host information processing apparatus 200 calculates the image data compression ratio C _Preview of the preview image in the designated reading range, and reads the read with the requested main scan resolution (Ndpi) by means described later. Estimated image data compression ratio C _MainScan (N) when performed, and using this estimated compression ratio, the image data amount V [bytes] when uncompressed in the specified reading range and reading resolution, From the given interface transfer rate R [bytes / second], the shortest compressed image data transfer time S _min is calculated by the following equation 1 (step S209).

S _min = V × C _MainScan (N) / R [seconds] (Equation 1)
The host information processing apparatus 200 notifies the image reading apparatus 100 of the minimum reading time calculated by the above formula 1 together with the designation of the reading range and the reading resolution (step S210), and instructs the start of reading the main scan image (step S210). S211).

  The image reading apparatus 100 receives data such as the image reading range, the reading resolution, and the minimum reading time calculated by the above equation 1 (step S257), prepares an image reading operation under the specified parameter conditions, and performs the main scan. A reading operation is started in accordance with an image reading start instruction (step S258).

  The image reading apparatus 100 transmits the compressed image data to the host information processing apparatus 200 while compressing and encoding the image data in the same manner as when reading the preview image, and executes the main scan image data reading at an appropriate reading speed ( Step S259). Similarly to the preview image reading, the host information processing apparatus 200 receives the compressed image data (step S212) and decompresses and decodes (step S214), and stores the image in the image storage unit 203 (see FIG. 1) (step 1). S214).

  The decompression decoding (step S214) of the compressed image may be performed in parallel with the image data reception (step S212), or the decompression and decompression may be performed collectively after the reception of all the image data is completed.

  When reading a new document continuously, the procedure from step S201 is repeated.

  Even when the data compression rate changes depending on the original image read in this manner, an appropriate reading speed can be estimated and used based on the compression rate of the preview image obtained in advance. Also, the amount of compressed image data varies depending on the content of the original document, but since the preview image is normally read at a low resolution, the amount of compressed image data is sufficiently small. It is possible to read at a reading speed defined by the mechanical and electrical restrictions.

  In the operation of the image reading apparatus 100 according to the present embodiment described above, it is applied to compression processing of an image transmitted from the image reading apparatus 100 and decompression decoding processing in the host information processing apparatus 200 that has received the compressed data. The compression coding technique is generally known, and the details thereof are not related to the novelty of the present invention, so detailed description will not be given here. For example, one line of image data is blocked. A method of obtaining image data compressed by a means for encoding by performing entropy encoding after quantization is conceivable.

  In the above description, the compression rate is estimated by the host information processing apparatus 200. However, in the usage method in which the entire surface of the original is always read without specifying the reading range, the image reading apparatus 100 estimates the compression rate. It is also possible to configure so that

  Next, the procedure for estimating the image data compression rate in the image reading apparatus 100 according to the present embodiment will be described in detail while explaining the difference in compression rate due to the difference in resolution by giving specific examples of various documents.

  FIG. 3 shows a scanning ratio of 150 dpi (main scanning resolution) obtained by reading each original including text documents and photographic originals at 100 dpi (preview resolution) and compressing by the first Huffman compression encoding method. The vertical axis represents the compression rate at the time of reading, and the correlation of the compression rate due to the difference in resolution is displayed on the correlation graph for various images.

  However, 1/4 is the maximum compression rate due to the characteristics of the quantization table and the coding table used.

It can be seen from FIG. 3 that the images are arranged on a straight line passing through (0.25, 0.25) with a slight inclination of 1, regardless of the content of the original image. Therefore, the compression rate C _MainScan (150) when reading at 150 dpi can be estimated from the preview image compression rate C _Preview when reading at 100 dpi, and the following equation 2 is obtained by the method of least squares.

C _MainScan (150) = K (150) × C _Preview + B (150) (Formula 2)
However,
K (150) = 0.87, B (150) = 0.03
Similarly, FIG. 4 shows the correlation between the compression rate of the image read at 300 dpi and the compression rate at the preview resolution, and FIG. 5 shows the correlation between the compression rate of the image read at 600 dpi and the compression rate at the preview resolution.

According to FIGS. 4 and 5, it can be seen that the straight lines have different slopes as in FIG. The compression ratio C _MainScan (300) for reading at 300 dpi and the compression ratio C _MainScan (600) for reading at 600 dpi can be estimated from the preview data compression ratio C _Preview by the following formulas 3 and 4 by the least square method. Is possible.

C _MainScan (300) = K (300) * C _Preview + B (300) (Formula 3)
C _MainScan (600) = K (600) * C _Preview + B (600) (Formula 4)
However,
K (300) = 0.79, B (150) = 0.05
K (600) = 0.56, B (150) = 0.11
The result calculated based on the above Equations 2 to 3 is displayed in the graph of FIG.

  Here, the description has been made taking up the estimation of the compression rate of image data at 150 dpi, 300 dpi, and 600 dpi, but the same method can be applied to other resolutions.

  As described above, according to the image reading apparatus 100 according to the present embodiment, the image data compression rate at the preview resolution and the respective reading resolutions for each compression encoding algorithm used for compression encoding of the read image data. A function representing the correlation of the image data compression rate can be obtained in advance by a statistical method, and the image compression rate during the main scan can be appropriately estimated from the compression rate in the preview image in the reading target range and the main scan reading resolution. Therefore, even when image data is compressed, a reading operation that makes full use of the bandwidth of the interface becomes possible.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS.

  The basic configuration of the image reading apparatus according to the present embodiment and the information processing system having the image reading apparatus is the same as that in FIG. 1 in the first embodiment described above. I will explain.

  The image reading apparatus according to the present embodiment has a function of determining whether a read target original is a halftone print original, a text document, or a photo original based on a preview image read at a low resolution. In the case of a printed document, it has a function of reading without compression.

  The operation of the image reading apparatus according to this embodiment will be described below with reference to FIG.

  FIG. 7 is a flowchart showing an operation flow of the information processing system having the image reading apparatus according to the present embodiment.

  In FIG. 7, steps S751 to S760 which are processing steps on the image reading apparatus 100 side are the same as steps S251 to S260 which are processing steps on the image reading apparatus 100 side in FIG. 2 of the first embodiment described above. In FIG. 7, steps S701 to S708, steps S713 to S715, and S719, which are processing steps on the host information processing apparatus 200 side, are the image reading apparatus 100 in FIG. 2 of the first embodiment described above. Since these steps are the same as steps S201 to S208, steps S210 to S212, and S215, which are the processing steps on the side, their descriptions are omitted, and only the processing steps unique to the present embodiment are described.

  The host information processing apparatus 200, which sequentially executes Steps S701 to S707 and receives the main scan start request in Step S708, determines whether the preview image in the specified reading range is a document original image, a photographic photographic paper original, or a halftone dot. It is determined whether the document is a printed document (step S709).

  Note that various methods for determining the document type have been proposed in the past, and a detailed description thereof will be omitted here.

  If the determination result of the preview image is other than the halftone print original (step S710), it is estimated that the amount of image data can be reduced by using the compression encoding means (image compression function). As described in the first embodiment, the compression rate of the main scan is predicted from the image data compression rate at the preview resolution and the image data compression rate at each reading resolution, and the compressed image data amount and the reading speed are determined. (Step S711).

  On the other hand, if it is determined in step S710 that the document is a halftone print original, it is predicted that the primary Huffman encoding method cannot be compressed properly, and the data amount is increased as compared with the case of non-compression. Therefore, the document image reading that does not use the compression encoding means is selected (step S712).

  Thereafter, the host information processing apparatus 200 determines whether or not the image compression process is designated after executing the processes of steps S713 to S715 (step S716). When the image compression processing is designated (step S716), the image on which the image data has been decompressed and decoded is stored in the image storage unit 203 (see FIG. 1) (step S718). If the image compression is not designated (step S716), the received image is stored in the image storage unit 203 (step S717), and after executing step S719, the series of image reading operations is terminated.

  Note that the decompression decoding of the compressed image may be performed in parallel with the reception of the image data, or the decompression and decompression may be performed collectively after the reception of all the image data is completed.

  When reading a new document continuously, the procedure from step S701 is repeated.

  FIG. 8 shows a correlation between the compression ratio of an image obtained by reading various originals including halftone printed originals at 300 dpi by the image reading apparatus 100 according to the present embodiment and the compression ratio at the preview resolution. FIG. The correlation between the compression ratio of an image obtained by reading various originals including a halftone print original at 600 dpi by the image reading apparatus 100 according to the embodiment and the compression ratio at the preview resolution is shown.

  In FIG. 8 and FIG. 9, the compression ratio of the photographic original (printed paper original) indicated by □, ◇, and Δ and the compression ratio of the character original indicated by the ◯ symbol are primarily distributed, The compression rate of the halftone dot printed document indicated by the x and + symbols is close to 1 at high resolutions of 300 dpi and 600 dpi even when the compression rate of the preview image is about 0.66. The amount of data increases due to the encoding process).

  As described above, when the compression effect does not increase sufficiently due to the combination of the characteristics of the document to be read and the compression encoding means to be used, other types can be avoided while communicating uncompressed images while avoiding harmful effects. Thus, it is possible to obtain an effect such as shortening the reading time for the original image.

  In the present embodiment, the image reading apparatus having only one compression encoding unit has been described from the viewpoint of whether or not the compression unit can be used. In an image reading apparatus including a switching unit that switches between a compression compression processing unit and a compression unit that are adapted for use, by selectively using a compression encoding unit that is optimal for a halftone print original and other originals, More effective operation becomes possible.

  As described above, according to the image reading apparatus of the present embodiment, whether or not the compression encoding means used for the compression encoding of the read image data can be used, or the selective use of a plurality of compression encodings is determined based on the preview image. The image data compression function is exhibited for many other documents while avoiding the disadvantages caused by the compression coding means that does not match the characteristics of the document image. Thus, it is possible to perform a reading operation making full use of the bandwidth of the interface.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIG.

  The basic configuration of the image reading apparatus according to the present embodiment and the information processing system including the image reading apparatus is the same as that in FIG. 1 in the first embodiment described above. I will explain.

  The image reading apparatus according to the present embodiment has transmission means for transmitting pseudo image data at the upper limit speed of the interface band without accompanying a document image reading operation, and a host information processing apparatus such as a personal computer (personal computer) or the like It is characterized in that it has a function of measuring the execution transfer rate with the image reading apparatus prior to reading the image.

  Hereinafter, the operation of the image reading apparatus according to the present embodiment will be described with reference to FIG. FIG. 10 is a flowchart showing an operation flow of the information processing system having the image reading apparatus according to the present embodiment.

Prior to the instruction to start reading the preview image, the host information processing apparatus 200 requests the image reading apparatus 100 to transmit uncompressed pseudo image data together with the designation of the data amount V _test [bytes] to be transmitted (step S1001). (Step S1002).

The image reading apparatus 100 that has been waiting for operation (step S1051) prepares for data transmission according to a pseudo image transmission instruction and data amount designation (step S1052), and starts transmission of pseudo data according to a transmission start instruction (step S1051). Step S1053). Thereafter, the host information processing apparatus 200 receives the pseudo image data while measuring the time T _test [seconds] required to receive all the data transmitted by the image reading apparatus 100 (step S1054) (step S1003) ( In step S1004 and step S1005), the interface execution transfer rate R _effect is calculated by the following equation 5 (step S1006).

R _effect = V _test / T _test [bytes / second] (Formula 5)
The host information processing apparatus 200 that has obtained the interface execution transfer speed with the image reading apparatus 100 performs processing according to the procedure (FIG. 2) described in the first embodiment described above. In addition to the procedure described in the embodiment, in particular, in the calculation of the compressed image data transfer time S _min according to (Equation 1) described in the first embodiment, by selecting the reading speed by using the above result, Regardless of the operation state of the host information processing apparatus 200 or the use state of the interface, it is possible to perform an image reading operation at an optimum reading speed.

In addition, the measurement of the interface execution transfer rate R _effect is repeated a plurality of times, and if R _low obtained from the average value R _average and the standard deviation R _{std according} to the following equation 6 is used, high-quality reading with little pause in reading scanning is performed. Can be expected.

R _low = R _average −R _std (Formula 6)
[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described with reference to FIGS.

  The basic configuration of the image reading apparatus according to the present embodiment and the information processing system having the image reading apparatus is the same as that in FIG. 1 in the first embodiment described above. explain.

  The image reading apparatus according to the present embodiment predicts the compressed image data amount that matches the document content by estimating the compression rate at each sub-scanning position of the document image based on the preview image read at a low resolution. It has the function to perform.

  Hereinafter, the operation of the image reading apparatus according to the present embodiment will be described with reference to FIG.

  FIG. 11 is a flowchart showing an operation flow of the information processing system having the image reading apparatus according to the present embodiment.

  11, step S1151 to step S1155 and step S1157 to step S1161 that are processing steps on the image reading apparatus 100 side are step S251 that are processing steps on the image reading apparatus 100 side in FIG. 2 of the first embodiment described above. Are the same as steps S255 and S257 to S261, and in FIG. 7, steps S1101 to S1105, steps S1107 to S1109, and steps S1112 to S1117, which are processing steps on the host information processing apparatus 200 side, Steps S201 to S205, Steps S207 to S209, and Steps S212 to Steps that are processing steps on the image reading apparatus 100 side in FIG. 2 of the first embodiment described above. S217 and because it is the same, the description thereof is omitted, and only describes the form specific processing steps of the present embodiment.

  The image reading apparatus 100 that has completed reading of the document image in the range specified by the preview reading parameter is processed at each sub-scanning position recorded and stored in the memory area inside the image reading apparatus 100 before and after the process of step S1155. The data amount history of the compression-encoded image is transmitted to the host information processing apparatus 200 (step S1156). Thereafter, the image reading apparatus 100 sequentially executes Steps S1157 to S1161.

  On the other hand, the host information processing apparatus 200 that has completed the reception of the compressed image data (step S1104) and the decompression / restoration (step S1105) performs a preview image display (step S1107) on the image display means 204 (see FIG. 1). Then, the data amount history of the compression-coded image at each sub-scanning position recorded and stored in the memory area inside the image reading apparatus 100 is received (step S1106).

  After that, the host information processing apparatus 200 that has sequentially executed the processing of step S1108 to step S1109 calculates the image data compression rate CPreview (y) at each position y of the preview image in the designated reading range, and will be described in detail later. Thus, the transition CMainScan (Ny) of the estimated image data compression rate when reading is performed at the requested main scan resolution (Ndpi) is estimated (step S1110).

  Subsequently, the host information processing apparatus 200 determines the image data amount V [bytes] at the time of non-compression with the specified reading range and reading resolution, the given interface transfer rate R [bytes / second], and the image buffer memory 106. An optimum reading speed is calculated from the capacity (see FIG. 1) (step S1111). The contents of this process will be described later.

  Thereafter, the host information processing apparatus 200 sequentially executes Steps S1112 to S1117.

  With the configuration described above, even when the data compression rate changes at each sub-scanning position of the original image to be read, a given capacity of the image buffer memory 106 is obtained from the compression rate at each position of the preview image obtained in advance. It is possible to select and use the most suitable reading speed. Also, the amount of compressed image data varies depending on the content of the original document, but since the preview image is normally read at a low resolution, the amount of compressed image data is sufficiently small. It is possible to read at a reading speed defined by the mechanical and electrical restrictions.

  In the operation of the image reading apparatus 100 according to the present embodiment described above, it is applied to the compression process of the image transmitted from the image reading apparatus 100 and the decompression decoding process in the host information processing apparatus 200 that has received the compressed data. The compression coding technique is generally known, and the details thereof are not related to the novelty of the present case. Therefore, detailed explanation will not be given here, but as an example, one line of image data is assumed to be a block. A method of obtaining compressed image data by means of encoding by entropy encoding after quantization is conceivable.

  In the above description, the transition of the compression rate and the selection of the reading speed are performed by the host information processing apparatus 200. However, in a usage method in which the entire original is always read without specifying the reading range, The image reading apparatus 100 may be configured to perform compression rate estimation and reading speed selection.

  Next, the transition of the image data storage amount in the image data buffer memory 106 (see FIG. 1) when the compression ratio changes at each position of the read document will be described in the present embodiment while explaining the transition of the amount of image data with numerical examples. An image reading speed selection procedure in the image reading apparatus 100 will be described in detail.

  FIG. 12 is a graph for specifically explaining the transition of the compression ratio of an image, and an example of a read image is shown in the upper part. The line image sensor 101 (see FIG. 1) is arranged in the vertical direction of the read image, and reading of the image proceeds from the left end of the read image to the right.

  In the lower part of FIG. 12, the transition of the compression rate of the compression encoding is displayed corresponding to each position of the read image in the upper part.

  Note that since the lower limit of quantization and encoding in the compression encoding means provided in the image reading apparatus 100 according to the present embodiment is ¼, the minimum compression rate in FIG. 12 is 0.25.

  In FIG. 12 (1), the luminance information of the photographic image range is input to the image sensor 101, so that the compression rate is increased to about 0.5 to 0.6. After that, it becomes a grassland image area, the compression ratio deteriorates due to the increase in fine changes, and after increasing to about 1.05 near (2), the photo image ends in (3) and becomes a white background area Therefore, the compression rate is improved to 0.3 or less. (4) and (5) show the deterioration of the compression rate in the portion corresponding to the character range in the white background.

  Next, data predicted to be stored in the image data buffer memory 106 (see FIG. 1) at each reading position from the transition CMainScan (Ny) of the estimated compression rate of the image data at each position y within the designated reading range. A change in the amount Vbuffer (y) and the influence of the change on the operation of the image reading apparatus 100 will be described.

  The data amount Vbuffer (y) predicted to be stored in the buffer at the image position y is calculated by the following recurrence formula 1.

(Recursion formula 1)
Vbuffer (0) = 0
ΔB = B * Cext (y) / T Ractual
ΔVbuffer (y) = if (Vbuffer (y−1)> 0) then ΔB
else if (ΔB> 0) thenΔB
else0
Vbuffer (y) = Vbuffer (y-1) + ΔVbuffer (y)
If (Vbuffer (y) <0) thenVbuffer (y) = 0
However,
Interface effective transmission rate Ractual [bytes / second],
Amount of uncompressed data in unit block (line) B [bytes]
Time T [second] to move the unit block (line)
Data balance in the unit block (line) ΔB [bytes]
Estimated compression rate Cext (y) at image position (image block number) y
Amount of data ΔVbuffer (y) predicted to be newly accumulated in the buffer at the image position y
A data amount Vbuffer (y) that is predicted to be stored in the buffer at the image position y.

  FIG. 13 shows a transition Vbuffer (y) graph of the amount of data accumulated in the image buffer memory 106 when the average compression rate is selected as the reading speed at the interface effective transmission speed. Show.

  As shown in FIG. 13, in a manuscript in which photographs and characters are mixed, a photographic image area, in particular, a minute image such as (10), (11), (12) tree branches and grassland images in FIG. In order to continuously exceed the average compression rate within a range having a change, the amount of compressed data stored in the image buffer memory 106 is remarkably increased, and the image buffer memory 106 having a sufficient capacity is required.

  Next, an image buffer memory for reading at a reading speed capable of transmitting a compressed image of 1.2 times the average compression rate at the interface effective transmission speed, that is, at a reading speed of 1 / 1.2 in the case of FIG. FIG. 14 shows a graph of the transition Vbuffer (y) of the amount of data stored in 106.

  As shown in FIG. 14, the necessary amount of the image buffer memory 106 is reduced to less than half by reducing the reading speed by a little less than 20%, or the pause of the reading operation due to the empty space in the image buffer memory 106 is predicted and avoided. Is possible.

  As described above, if the maximum value of Vbuffer (y) is less than or equal to the capacity Vmax of the image buffer memory 106, the reading speed that matches the compression coding characteristics of the read image is selected while optimally using the bandwidth of the interface. At this time, the highest image quality is also obtained.

  As a reading speed selection algorithm, for example, the following rules can be considered using C language notation.

  The algorithm is as follows, where Tmin is the minimum T resulting from the restrictions of the reading mechanism and the circuit, and the optimization degree of the reading speed is K (= 1.1).

(Algorithm 1)
for (T = Tmin, T <Tmax, T = T × K) {
Vbuffer = 0
for (y = 1, y <Length, y ++) {
dB = B × Cext (y) / T-Ractual
if (Vbuffer> 0) {
dVbuffer = dB
} else if (dB> 0) {
dVbuffer = dB
} else
dVbuffer = 0
Vbuffer = Vbuffer + dVbuffer
if (Vbuffer <0) Vbuffer = 0
if (Vbuffer> Vmax) break;
}
if (Y = Length) break;
}
In the above algorithm, the transition of the amount of data stored in the image buffer memory 106 when reading is performed at a speed due to hardware restrictions of the image reading apparatus 100 is calculated using the variable Vbuffer, and the image is read in the entire image reading range. When the capacity Vmax of the buffer memory 106 is not exceeded, the speed is selected, and when the capacity Vmax of the image buffer memory 106 is exceeded, a process of recalculating at a speed about 10% slower is set as a condition. It repeats until it meets.

  As described above, according to the image reading apparatus 100 according to the present embodiment, the compression rate at each reading position of a relatively low resolution preview image that is executed in advance is measured, and the target reading resolution is obtained. By predicting the transition of the compression ratio of the original image, the amount of use of the image buffer memory 106 that matches the original content can be obtained, so that a more accurate reading speed can be obtained and the image reading apparatus 100 is provided. Further, it is possible to realize transfer of image data that makes the best use of the bandwidth of the image buffer memory 106 and the interface circuit 105.

[Other embodiments]
The above is the description of the embodiments of the present invention. However, the present invention is not limited to these embodiments, and may be configured to achieve the functions shown in the claims or the functions of the configurations of the embodiments. Anything is applicable.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and store the computer (or CPU, MPU, etc.) of the system or apparatus. Needless to say, this can also be achieved by reading and executing the program code stored in the medium. In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium and program storing the program code constitute the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like is used. it can.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

1 is a block diagram showing a schematic configuration of an information processing system having an image reading apparatus according to a first embodiment of the present invention. 3 is a flowchart showing an operation flow of the information processing system having the image reading apparatus according to the first embodiment of the present invention. 5 is a graph showing a correlation between a compression rate of an image read at 150 dpi and a compression rate at a preview resolution in the image reading apparatus according to the first embodiment of the present invention. 6 is a graph showing a correlation between a compression rate of an image read at 300 dpi and a compression rate at a preview resolution in the image reading apparatus according to the first embodiment of the present invention. 6 is a graph showing a correlation between a compression rate of an image read at 600 dpi and a compression rate at a preview resolution in the image reading apparatus according to the first embodiment of the present invention. 5 is a graph for explaining the main scan compression ratio estimation from the compression ratio at the preview resolution in the image reading apparatus according to the first embodiment of the present invention. 6 is a flowchart illustrating an operation flow of an information processing system including an image reading apparatus according to a second embodiment of the present invention. FIG. 10 is a diagram illustrating a correlation between a compression ratio of an image obtained by reading various originals including a halftone print original at 300 dpi and a compression ratio at a preview resolution in the image reading apparatus according to the second embodiment of the present invention. FIG. 6 is a diagram illustrating a correlation between a compression ratio of an image obtained by reading various originals including a halftone print original at 600 dpi and a compression ratio at a preview resolution in the image reading apparatus according to the second embodiment of the present invention. 10 is a flowchart showing an operation flow of an information processing system having an image reading apparatus according to a third embodiment of the present invention. 10 is a flowchart showing an operation flow of an information processing system having an image reading apparatus according to a fourth embodiment of the present invention. It is a graph which demonstrates concretely the transition of the compression rate of the image in the image reading apparatus which concerns on the 4th Embodiment of this invention. 14 is a graph for specifically explaining the data accumulation amount in the image buffer memory when the reading speed is selected based on the transition of the image compression rate and the average compression rate in the image reading apparatus according to the fourth embodiment of the present invention. 14 is a graph for specifically explaining the amount of data stored in the image buffer memory when a reading speed of 1 / 1.2 in FIG. 13 is selected.

Explanation of symbols

100 Image Reader 101 Line Image Sensor (CCD)
102 A / D converter 103 Image processing circuit 104 Compression encoding circuit 105 Interface circuit 106 Image buffer memory 107 CPU
110 Interface communication path 200 Image information processing apparatus (host information processing apparatus)
201 Interface circuit 202 Compressed data decoding means 203 Image storage means 204 Image display means

Claims (14)

Image reading that reads the image on the original by moving the original or the reading optical system in a direction perpendicular to the arrangement direction of the photoelectric conversion elements while converting the density information of the original to be converted into an electrical signal by the photoelectric conversion element. In the method
A compression encoding process for compressing and encoding image data;
A compression rate estimation step of estimating the compression rate at the time of reading the main image from the compression rate of the pre-scanned image;
An image reading method comprising: a reading speed selection step of selecting an optimum reading speed for a read original image from the compression ratio estimated by the compression ratio estimation step and an execution transfer speed of the interface. A communication process for communicating pseudo image data without scanning operation between the image reading device and the host information processing device;
The image reading method according to claim 1, further comprising: a calculation step of calculating an execution transfer rate of the interface from a result of communication in the communication step.   When it is predicted that the estimated compression rate when reading the main image is close to 1 or the amount of data is increased by the compression encoding process in the compression encoding process, the image data compression process when reading the main image is performed. The image reading method according to claim 1, further comprising a control step of controlling so as not to occur.   A document type determining step for determining a document type of the pre-scanned image, and the control step does not perform the compression process when the document type determining step determines that the document is a halftone printed document. The image reading method according to claim 1, wherein the image reading method is controlled.   A plurality of compression encoding steps, a compression encoding selection step for selecting and using one of these compression encoding steps, and the compression encoding selection step having the highest compression efficiency for each document type 5. The image reading method according to claim 1, wherein a compression encoding step is selected. An image reading method for reading an image on a document by moving the document or a reading optical system in a direction perpendicular to the arrangement direction of the photoelectric conversion elements while converting density information of the read document into an electrical signal by a photoelectric conversion element. In
A compression encoding process for compressing and encoding image data;
A recording step for recording and storing the compression rate of the image information compressed by the compression encoding step;
A compression rate estimation step of estimating a compression rate under different reading conditions from the compression rate recorded and stored by the recording step;
An image reading method comprising: a sub-scanning speed selecting step of selecting an optimum sub-scanning speed based on an output of the compression ratio estimating step and an execution transfer speed of a given interface. Image reading that reads the image on the original by moving the original or the reading optical system in a direction perpendicular to the arrangement direction of the photoelectric conversion elements while converting the density information of the original to be converted into an electrical signal by the photoelectric conversion element. In the device
Compression encoding means for compressing and encoding image data;
Compression rate estimating means for estimating the compression rate at the time of reading the main image from the compression rate of the pre-scanned image;
An image reading apparatus comprising: a reading speed selecting means for selecting an optimum reading speed for a read original image from the compression ratio estimated by the compression ratio estimating means and an execution transfer speed of the interface. Communication means for communicating pseudo image data without a scanning operation between the image reading apparatus and the host information processing apparatus;
The image reading apparatus according to claim 7, further comprising: an arithmetic unit that calculates an execution transfer rate of the interface from a result of communication by the communication unit.   When the estimated compression rate at the time of reading the main image is close to 1 or when it is predicted that the amount of data will increase due to the compression coding process by the compression coding means, the image data compression process at the time of reading the main image is performed. The image reading apparatus according to claim 7, further comprising a control unit configured to perform control so as not to occur.   Document type determination means for determining the document type of the pre-scanned image, and the control means does not perform compression processing when the document type determination means determines that the document is a halftone print document. The image reading apparatus according to claim 7, wherein the image reading apparatus is controlled.   A plurality of compression encoding units; and a compression encoding selection unit that selects and uses one of the compression encoding units. The compression encoding selection unit has the highest compression efficiency for each document type. 11. The image reading apparatus according to claim 7, wherein a compression encoding unit is selected. An image reading apparatus that reads an image on an original by moving the original or a reading optical system in a direction perpendicular to the arrangement direction of the photoelectric conversion elements while converting density information of the read original into an electrical signal by a photoelectric conversion element. In
Compression encoding means for compressing and encoding image data;
Recording means for recording and storing the compression rate of the image information compressed by the compression encoding means;
Compression rate estimation means for estimating the compression rate under different reading conditions from the compression rate recorded and stored by the recording means;
An image reading apparatus comprising: a sub-scanning speed selecting unit that selects an optimum sub-scanning speed based on an output of the compression rate estimating unit and an execution transfer speed of a given interface.   A program comprising computer-readable program code for realizing the image reading method according to claim 1.   A storage medium for storing computer-readable program code for realizing the image reading method according to claim 1.

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