An image reading method and apparatus therefor

Abstract: This image reading apparatus includes: light sources (4, 6), a line sensor(5) for photoelectrically converting light from an original image, a light source control section (10) for controlling the lighting time of each light source; a gamma correction section (17) for converting a photoelectrically converted electric signal to image data with a gamma function and a controller (19) for controlling the light source control section and the gamma correction section. The controller adjusts the lighting time T₁, T₂, T₃) of the light source or the gradient of the gamma function (Y₁, Y₂, Y₃) in response to a specified lightness from an external computer so that image data in such specified lightness can be obtained. For example, in the case of a dark image where the lightness is to be increased, if the user wishes a high quality image, the lighting time is increased to T2, whereas if the user attaches importance to high speed reading, the gradient of the gamma function is increased to Y₂. Further, in the case of a light image where the lightness is to be decreased, if the user wishes a high quality image, the gradient of the gamma function is decreased to Y₃, whereas if the user attaches importance to high speed reading, the lighting time is shortened to T₃.

Description: The present invention relates to an image reading system for converting the image of an original into an electric signal. An image reading apparatus of, e.g., flat bed type includes, as known well, an original image table constructed of a transparent board, a light source for irradiating an original image, and a line sensor having a multiplicity of photoelectric conversion elements. Such image reading apparatus irradiates a beam of light onto the original image placed on the original image table, detects reflected light or transmitted light while moving the line sensor, and converts density changes in the reflected or transmitted light from the original image into an electric signal. However, since an original image, from which only small reflected light or transmitted light is obtained, gives small input light intensity to the line sensor, the input light amount to the sensor (input light intensity x light storing time) becomes close to the noise level, which in turn imposes the problem of impaired image quality. To overcome this problem, an image reading apparatus has been proposed in, e.g.. Unexamined Japanese Patent Publication No. Hei. 4-335760. This image reading apparatus is provided to increase the level of a light amount signal from the line sensor by increasing the input light amount to the line sensor. The light storing time per line is increased in accordance with the density of an original, if the density of the original is high, as well as the input light intensity to the sensor is small. The light amount signal whose level has been increased, is converted into an image signal using a gamma function. According to this image reading apparatus, although the lightness of the original is increased, the original reading speed is reduced in proportion to the increase in the light storing time, which is a problem. In addition, the user has to alter the operation panel settings of the image reading apparatus in accordance with a change in density of an original every time the original is changed, which imposes another problem of cumbersome operation. To overcome these problems, proposed is a method of increasing the level of a light amount signal by increasing the irradiation intensity of a light source with the original reading speed kept at a conventional level. However, this method sacrifices the life of the light source to increase the irradiation intensity; i.e., the service life of the light source is inevitably shortened. US Patent 5173789 discloses a scanner which can be used as an input device to a television or like display so as to enable manual zooming and cropping of an image projected onto an image sensor. Since zooming of the image affects the level of illumination impinging upon the sensor, an automatic brightness circuit varies the illumination according to the signal level. A manually operated circuit allows additional user-selected variation of the illumination level. US Patent 5296944 discloses an image scanner in which a comparison is made between the level of an output signal and a reference level so as to enable correction of the dynamic range of the image scanner by controlling the amount of light which impinges upon the image sensor. The present invention has been made in consideration of the aforementioned circumstances. According to a first aspect of the present invention there is provided an image reading system comprising: a light source (4; 6) for irradiating an original image; reading means (5, 15) for receiving and converting reflected or transmitted light from the original image to an output signal; image converting means (16, 17, 18, 21) which convert the output signal to image data using one of a plurality of conversion functions each of which uses a different density sensitivity to obtain the image data; light adjusting means (12) which adjust the irradiation by the light source; control means (19) having mutually exclusive first and second selection means, the first selection means being coupled to said image converting means and the second selection means being coupled to said light adjusting means; display means for displaying the image data; lightness specifying means for specifying the lightness of the displayed image; the lightness specifying means being coupled to the control means such that subsequent to operation of the lightness specifying means said image converting means or said light adjusting means automatically performs an adjustment to adjust the image data to the specified lightness in dependence upon which of the first or second selection means is selected. According to a second aspect of the present invention there is provided a lightness adjustment method in an image reading system irradiating an original image using a light source (4; 6); receiving and converting reflected or transmitted light from the original image to an output signal using a reading means (5, 15); converting the output signal to image data using one of a plurality of conversion functions each of which uses a different density sensitivity to obtain the image data by using an image converting means (16, 17, 18, 21); displaying the image data on display means; specifying the lightness of the displayed image using lightness specifying means; subsequent to operation of the lightness specifying means operating a control means (19) to exclusively select an automatic adjustment to adjust the image data to the specified lightness either by changing to another of said plurality of conversion functions or by adjusting the irradiation by the light source. The image reading system according to the present invention is characterised as allowing the user to select either the first reading mode that produces image data having a desired lightness by adjusting the light amount signal outputted from the sensor as a result of operating either the lighting time of the light source or the interval of the shift pulse of the line sensor or the second reading mode that produces image data having the desired lightness through gamma function adjustment at the request of the user. For example, in the case where lightness is increased, and if the user attaches importance to image quality, then the user selects the first reading mode to adjust the lighting time of the light source or the interval of the shift pulse of the line sensor, so that high quality image data with high S/N ratio can be obtained, whereas if the user attaches importance to reading time, then the user selects the second reading mode to increase the gradient of the gamma function, so that the reading time is not increased. Further, in the case where lightness is decreased, and if the user wishes to prevent image quality from being impaired, then the user selects the second reading mode to decrease the gradient of the gamma function, whereas if the user wishes to shorten the reading time, then the user selects the first reading mode to adjust the lighting time of the light source or the interval of the shift pulse of the line sensor, so that the reading time can be shortened. In this way, the needs of the user can be flexibly accommodated even if the same lightness is to be obtained. It is preferred that this apparatus be designed so that when the first reading mode is selected by the user, the lighting time of the light source or the interval of the shift pulse of the line sensor is adjusted automatically, and that when the second reading mode is selected by the user, the gamma function is adjusted automatically. As a result of this design, the user can obtain a desired output image only by specifying lightness, which is visibly checked with ease and which is one of the most important factors for the user and selecting the reading mode without having to deal with cumbersome factors such as the light source and the gamma function at all. It is preferred that adjustments using an arbitrary gamma function be made available for reading operations by downloading such gamma function to the image reading apparatus from the external apparatus, in addition to adjustments made by the method programmed in advance in the image reading apparatus. This further increases freedom in the reading operation. Still further, the method according to the second aspect of the invention is characterised as displaying a result obtained by subjecting an original to the preliminary reading operation using the image reading apparatus while sending such result to the external apparatus such as a personal computer so that the user can input lightness adjustment data to the external apparatus after checking the displayed result of the preliminary reading operation. As a result of this operation, the lightness obtained as a result of the preliminary reading operation changes in accordance with the input on the display. Therefore, the user can determine an appropriate lightness by checking such change. The determined lightness is sent to the image reading apparatus, and an image in such lightness can be finally produced at a desired reading speed or with a desired image quality. Embodiments of the present invention will now be described with reference to the accompanying drawings, of which: Fig. 1 is a block diagram showing a general construction of a flat bed type image reading apparatus, which is an embodiment of the present invention; Fig. 2 is a block diagram showing a functional configuration of a light source control and sensor signal processing unit in the embodiment shown in Fig. 1; Fig. 3 is a diagram showing a relationship among the reflectance of an original, the sensor output, and the image signal level in the case where lightness is increased in the embodiment shown in Fig. 1; Fig. 4 is a diagram showing a relationship among the reflectance of an original, the sensor output, and the image signal level in the case where lightness is decreased in the embodiment shown in Fig. 1; and Figs. 5 (a), (b) and (c) are timing charts showing relationships in timing among the lighting of a lamp, the sensor output, and the shift pulse in the embodiment shown in Fig. 1. Fig. 1 shows a general construction of a flat bed type image reading apparatus, which is an embodiment of the present invention. An original table 1, formed of a transparent board such as glass, is provided on the upper surface of a box like frame 2. Inside the frame 2 is a carriage 3, which is moved-in parallel with the original table 1 by a driving unit (not shown). The carriage 3 has a light source 4 and a line sensor 5 therein. A beam of light irradiated from the light source 4 is reflected by the surface of an original 8 placed on the original table 1, and the reflected light is converged onto the line sensor 5 by a converging lens 7. It may be noted that a charge stored optical sensor such as a CCD can be used as the line sensor 5. Although not always necessary, there is above the original table 1, a second light source 6 that similarly moves in association with the movement of the carriage 3 to read a transparent original such as a photographic film. The number of the light source and the number of the line sensor are not limited by this embodiment. It is applicable to employ a plurality of light sources and a plurality of the line sensors. Fig. 2 shows a functional configuration of a light source control and sensor signal processing unit in the thus constructed image reading apparatus. In Fig. 2, a light source control section 10 controls the lighting time of the light source 4 or 6 based on time data read from a lighting time storage section 13 in response to control made by a controller 19, which will be described later. A control signal from this light source control section 10 is outputted to an inverter 11 so that the inverter 11 turns on the light source 4 or 6 for the selected time. The lighting time storage section 13 stores at least three kinds of time data. That is, a standard lighting time T1, a second lighting time T2 that is 1.6 times the standard lighting time T1, and a third lighting time T3 that is 1/1.6 times the standard lighting time T1. A CCD control section 12 generates a shift pulse in synchronism with the lighting timing of the light source 4 or 6, and controls the reading operation by the line sensor 5 in accordance with the carriage 3 operating speed. An A/D conversion section 15 converts a light amount signal received from the line sensor 5 through an amplifier 14, into a digital signal, and delivers the converted signal to a shading correction section 16. The shading correction section corrects, e.g., sensitivity variations per photoelectric element contained in the light amount signal from the line sensor 5. A gamma correction section 17 selects one from a plurality of kinds of gamma functions stored in a gamma function storage section 18 based on a signal from an external apparatus (e.g., a personal computer), and converts the corrected light amount signal from the shading correction section 16 into an image signal using the selected gamma function. The gamma function storage section 18 stores at least three kinds of gamma functions: a standard gamma function Y1, a high density original gamma function Y2, and a low density original gamma function Y3. The standard gamma function Y1 converts the total range of a light amount signal from the line sensor 5 into an image signal under high linearity (see Fig. 3). The high density original gamma function Y2 converts mainly the low range of a light amount signal into an image signal of higher level compared with the standard gamma function Y1 (see Fig. 3). The low density original gamma function Y3 converts the total range of a light amount signal into an image signal of lower level compared with the standard gamma function Y1 (see Fig. 4). The controller 19 is constructed of a microcomputer including a CPU, a RAM, and a RUM, and connected to an external image processing apparatus, e.g., a personal computer, through an interface 20. The controller 19 controls the lighting time of the light source 4 or 6, and selects a gamma function in response to a command from the personal computer. It may be noted that reference numeral 21 denotes a correction section for making conversions such as colour correction, edge enhancement, and enlargement/reduction of a region. An operation of the thus configured apparatus will be described next. A user connects a personal computer (not shown) to the interface 20 of this image reading apparatus, puts the original 8 on the original table 1, and gives a preliminary reading operation command from the personal computer. By the term "preliminary reading operation" it is intended to mean the operation of roughly reading the original image in order to specify the reading range, select the reading lightness, and the like prior to an image data reading operation desired by the user (hereinafter referred to as "detailed reading operation"). Once the preliminary reading operation command is given, the controller 19 turns on the light source 4 (the light source 6 in the case of reading a transparent original) only for the standard lighting time T1 at respective read line positions while sequentially moving the carriage 3 to the respective read line positions. As a result of this operation, an amount of charges (signal charges) proportional to a reflectance (or transmittance) of the original 8 at each read line position is stored in the line sensor 5. The controller 19 outputs a shift pulse to the CCD control section 12 upon elapse of the lighting time T1 at each line read position, so that not only the charges stored in the line sensor are sequentially applied to the amplifier 14 but also the carriage 3 is moved to the next read line position at a predetermined speed. The reading operation timings for this case are shown in Fig. 5 (a). An output signal V from the line sensor 5 is converted into a digital light amount signal by the A/D conversion section 15 after amplified by the amplifier 14, then outputted to the shading correction section 16, and subsequently applied to the gamma correction section 17 to be converted into an image signal I with the standard gamma function Y1 This image signal I is outputted to the personal computer through the interface 20, and displayed on a display. If the user is agreeable with the lightness of the image which has been subjected to the preliminary reading operation with the standard settings T1, Y1 and displayed, then the user gives a detail reading operation command. As a result, the image reading apparatus not only irradiates a beam of light onto the original for the standard lighting time T1, but also performs the detailed reading operation with the standard gamma function Y1. The reading operation timings for this case are shown in Fig. 5 (a). As a result of the detailed reading operation performed with the standard settings T1, Y1, an original with a density of d1 is outputted as a signal whose output level is V1 from the line sensor 5 as shown in Fig. 3. This signal, after subjected to predetermined processing at the amplifier 14, the A/D conversion section 15, and the shading correction section 16, is inputted to the gamma correction section 17. The thus processed signal is corrected with the selected standard gamma function Y1 in the gamma correction section 17 and the corrected signal is outputted as an image signal whose level is I1. On the other hand, in the case where the user wishes to have image data processed somewhat lighter because the illuminance of the image displayed as a result of the preliminary reading operation is low (e.g., an inadequately exposed photograph), the user takes the steps of setting the lightness one level higher, and then sending a detailed reading operation command signal from the computer to the image reading apparatus. That is to say for use with dark images. Then, the controller 19 of the image reading apparatus not only instructs the light source control section 10 to set the standard lighting time T1 as the lighting time, but also directs the gamma correction section 17 to select the high density original gamma function Y2 as the gamma function, so that the image reading apparatus starts the detailed reading operation. It may be noted that the high density original gamma function Y2 has, as shown in Fig. 3, a gradient of the image signal level with respect to the sensor output 1.6 times the standard gamma function Y1. As a result of this operation, as shown in Fig. 3, while the image signal of the original whose density is d1 is converted into a signal whose level is V1 from the line sensor 5 as described above, an image signal I2 having a higher level than the image signal processed with the standard gamma function is obtained in this case since the high density original gamma function Y2 whose gradient with respect to the sensor output is 1.6 times the standard gamma function is used. It may be noted that an image signal from a dark image can be obtained without increasing the time required for reading since the standard lighting time T1 is used as the lighting time in this case. However, it is not only the signal component but also noise component contained in the sensor output that are regularly converted with the gamma function Y2 in this case. Therefore, the noise component becomes noticeable in the image signal. Thus, a detailed reading operation with increased lightness and suppressed noise is required in some cases depending on the image quality of an original or on the use of an image signal. In such a case, the user inputs both a lightness increase command and a high image quality reading operation command at the same time to the personal computer and sends such commands to the image reading apparatus. In response thereto, the controller 19 of the image reading apparatus not only instructs the gamma correction section 17 to select the standard gamma function Y1, but also selects a lighting time longer than the standard lighting time T1, e.g., the lighting time T2 that is 1.6 times longer than T1 if lightness is to be set one level higher, and directs the light source control section 10 to select such lighting time T2, so that the image reading apparatus starts the detailed reading operation with such settings. The reading operation timings for this case are shown in Fig. 5 (b). When the original is irradiated for such a long time as the lighting time T2, the amount of charges stored in the line sensor 5 is increased in proportion to the lighting time. Therefore, as shown in Fig. 3, even if an original of the same density d1 has been read, the signal V outputted from the line sensor 5 becomes a large signal V2 that is about 1.6 times the signal obtained by using the standard lighting time T1. Hence, the image signal whose level is I2 can be obtained even if the standard gamma function Y1 is used. Although the reading time is increased since the longer lighting time T2 is used, a high quality, light image can be obtained. On the other hand, in the case where the density of an original is low and the lightness of the image displayed as a result of the preliminary reading operation performed with the standard setting is too high, the user takes the steps of setting the lightness one level lower, and then sending a detailed reading operation start signal from the computer to the image reading apparatus. In response thereto, the controller 19 of the image reading apparatus not only uses the standard gamma function Y1, but also selects the lighting time T3 that is 1/1.6 times the standard lighting time T1 as the lighting time of the lamp. The reading operation timings for this case are shown in Fig. 5 (c). As a result of this operation, a signal V3 whose level is T3/T1 (lighting time ratio) lower is outputted from the line sensor 5 as shown in Fig. 4. This signal V3 is converted into an image signal with the standard gamma function Y1, and an image signal I3 whose level is lower (darker) than in the case of using the standard lighting time T1 is outputted. In this case, the reading operation is ended within a shorter time than in the case of using the standard setting as much as the lighting time is shortened. If the user wishes a further improvement in the image quality than an improvement in the reading speed, then the user sends a high image quality reading command to the image reading apparatus from the computer. In response thereto, the controller 19 of the image reading apparatus not only uses the standard lighting time T1 as the lighting time, but also selects the low density original gamma function Y3 that has a lower gradient than the standard gamma function Y1. As a result of this operation, the image signal from the line sensor 5 has the same level V1 as in the case of using the standard setting as shown in Fig. 4. However, since the gradient of the gamma function Y3 is small, an image signal I3 that is smaller than that obtained by using the standard setting is obtained. In this case, noise is reduced compared with the case of using the shorter lighting time T3 since the standard lighting time T1 is used. Therefore, a high quality image can be obtained. As described above, this embodiment is characterised as allowing the user to specify a desired lightness after the user checks the result of the preliminary reading operation performed with the standard settings. The image reading apparatus then performs the detailed reading operation while automatically selecting the lighting time and the gamma function in response to the lightness specification so that an image of specified lightness can be outputted from the image reading apparatus. Therefore, the user can readily adjust the reading operation mode based on such a factor as lightness through which the user can easily recognise and estimate the current condition visually. That is, easy adjustment is an advantage. In addition, even if the same lightness is specified, the user can select a high speed reading mode or a high image quality reading mode, and the lighting time and the gamma function can be adjusted automatically in accordance with the selected mode. Therefore, the image reading apparatus of the present invention can provide a reading operation that meets user needs. It may be noted that if the user can simulate whether the specified lightness is appropriate or not, then the user can dispense with unnecessary repetition of detailed reading operations in setting the appropriate lightness. To do this, it is desired that special software be installed to the computer. The software being such as to process the image data displayed on the display as a result of the preliminary reading operation using the gamma function according to the specified lightness and display rough image data with lightness increased or deceased. Specifically, the software is set in such a manner that an increase in lightness to an increase in each value of image data R, G, B 1.6 times as much. If such values exceed the maximum (e.g., 255) that the image data can take, then it may, of course, be so processed that the image data is set to the maximum, and the image data may be so displayed on the display. That is, it is the software, not the image reading apparatus, that converts the image data with the same gamma function as the gamma function Y2 selected by the image reading apparatus. Further, while the value of a light amount signal is changed by adjusting the light source lighting time in this embodiment if the high image quality reading mode is selected, as a method equivalent thereto, it is, of course, possible to change the value of a light amount signal by adjusting the interval of a shift pulse of the line sensor while continuously turning the lamp on. While the above describes the embodiment of the present invention, the present invention may be embodied in various other modes. For example, instead of using the three kinds of lighting times and the three kinds of gamma functions in increasing or decreasing the level of lightness, a larger number of lighting times and gamma functions may be prepared so that finer lightness adjustments can be made. Still further, with respect to the gamma function, if the user can select or prepare a gamma function having an arbitrary gradient and shape using the computer in addition to the gamma functions prepared by the image reading apparatus and can use such selected or prepared gamma function for detailed reading operation by downloading such gamma function to the image reading apparatus, then freedom in reading is further increased. In this case, if software that can process image data that has been subjected to preliminary reading operation with the selected or prepared gamma function is installed to the computer, then the effect of the prepared gamma function can be simulated, which is an advantage for the user. As described in the foregoing, the present invention can provide an image reading apparatus that can read originals having different densities with desired lightnesses, and can meet image reading needs of the user by providing a high speed reading mode requiring a shorter reading time, a high image quality reading mode though the reading speed is not so high, or a like mode when such originals are to be read with desired lightnesses.

Claims: An image reading system comprising: a light source (4; 6) for irradiating an original image; reading means (5, 15) for receiving and converting reflected or transmitted light from the original image to an output signal; image converting means (16, 17, 18, 21) which convert the output signal to image data using one of a plurality of conversion functions each of which uses a different density sensitivity to obtain the image data; light adjusting means (12) which adjust the irradiation by the light source; control means (19) having mutually exclusive first and second slection means, the first selection means being coupled to said image converting means and the second selection means being coupled to said light adjusting means; display means for displaying the image data; lightness specifying means for specifying the lightness of the displayed image; the lightness specifying means being coupled to the control means such that subsequent to operation of the lightness specifying means said image converting means or said light adjusting means automatically performs an adjustment to adjust the image data to the specified lightness in dependence upon which of the first or second selection means is selected. An image reading system as claimed in claim 1, in which said control means controls said light adjusting means and said image converting means to effect one of the following: (i) increase the density sensitivity but not adjust the standard lighting time when the original image is dark; (ii) increase the lighting time but not the standard density sensitivity when the original image is dark to obtain an increased image quality; (iii) decrease the lighting time but not adjust the standard density sensitivity when the original image is light; and (iv) decrease the density sensitivity but not adjust the standard lighting time when the original image is light to obtain an increased image quality. An image reading system as claimed in claim 1 or 2, in which said conversion functions comprises gamma functions. An image reading system as claimed in claim 3, in which said image converting means includes means (18) for storing the plurality of gamma functions. An image reading system as claimed in any preceding claim, wherein said reading means comprises: rough reading means for roughly reading the original by reducing an amount of the data within a predetermined range of the original; and detailed reading means for performing a detailed reading operation with the specified lightness. An image reading system as claimed in any preceding claim, wherein the light adusting means adjusts a lighting time of the light source or an interval of a shift pulse of a line sensor. An image reading system as claimed in any preceding claim, wherein adjustment by the light adjusting means (12) effects a high image quality reading mode. An image reading system as claimed in any preceding claim, wherein adjustment by the image converting means (16, 17, 18, 21) effects a high speed reading mode. A lightness adjustment method in an image reading system irradiating an original image using a light source (4; 6); receiving and converting reflected or transmitted light from the original image to an output signal using a reading means (5, 15); converting the output signal to image data using one of a plurality of conversion functions each of which uses a different density sensitivity to obtain the image data by using an image converting means (16, 17, 18, 21); displaying the image data on display means; specifying the lightness of the displayed image using lightness specifying means; subsequent to operation of the lightness specifying means operating a control means (19) to exclusively select an automatic adjustment to adjust the image data to the specified lightness either by changing to another of said plurality of conversion functions or by adjusting the irradiation by the light source. A lightness adjustment method as claimed in claim 9, in which said automatic adjustment effects one of the following: (i) increase the density sensitivity but not adjust the standard lighting time when the original image is dark; (ii) increase the lighting time but not the standard density sensitivity when the original image is dark to obtain an increased image quality; (iii) decrease the lighting time but not adjust the standard density sensitivity when the original image is light; and (iv) decrease the density sensitivity but not adjust the standard lighting time when the original image is light to obtain an increased image quality. A lightness adjustment method as claimed in claim 9 or claim 10, wherein said use of said reading means comprises: reading the original by reducing an amount of the data within a predetermined range of the original; and performing a detailed reading operation with the specified lightness. A lightness adjustment method as claimed in any of claims 9 to 11, wherein adjusting the irradiation by the light source is effected by adjusting a lighting time of the light source or by adjusting an interval of a shift pulse of a line sensor. A lightness adjustment method as claimed in any of claims 9 to 12, wherein adjusting the irradiation by the light source effects a high image quality reading mode. A lightness adjustment method as claimed in any of claims 9 to 13, wherein changing to another of said plurality of conversion functions effects a high speed reading mode.

Inventors: ICHINOSE SHUICHI, KANESAKA YOSHINORI, ICHINOSE, SHUICHI, KANESAKA, YOSHINORI, ICHINOSE, SHUICHI, C/O SEIKO EPSON CORPORATION, KANESAKA, YOSHINORI, C/O SEIKO EPSON CORPORATION
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1995
Main classification: H04N1
IPC codes: G06T1, H04N1