Facsimile and static presentation processing – Facsimile – Facsimile measuring – testing – or calibrating
Reexamination Certificate
1998-11-06
2002-09-03
Coles, Edward (Department: 2622)
Facsimile and static presentation processing
Facsimile
Facsimile measuring, testing, or calibrating
C358S443000, C358S445000, C358S474000
Reexamination Certificate
active
06445469
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image reading device for use in a facsimile, a copying machine and a scanner, which device can read an image data from a specified area of an original document by using an original document reading mechanism such as a line sensor for reading image data from an original image at a specified time-interval based on a reference clock and a mechanism for moving the original document or the image reading mechanism.
Conventional facsimiles and copying machines, which read an original document image by using an image reading system using a line sensor consisting of linearly arranged image sensors such as CCDs, involve such a common problem that a distorted image may be produced due to fluctuation (variation) of document image scanning speed since the document or the reading head is mechanically moved in the feed (vertical scanning) direction.
Japanese Laid-Open Patent Publication No. 4-196964 discloses an image reading device that can detect a change in the scanning speed (fluctuation) by using a flowchart as shown in FIG.
1
.
The image reading device reads a document image together with an equal-pitch scale (reference scale) consisting of high-density and low-density lines of the same width, which lines are arranged alternatively at the same distance in the feed direction. Namely, its image-reading means such as a line sensor read the document image and the equal-pitch scale at the same time, detects read-time intervals of respective line-to-line distances of the scale (i.e., each distance from a high-density line to subsequent low-density line) and compares the detected time-intervals with the known reference value to determine the scanning speed fluctuation.
The essence of the art described in Japanese Laid-Open Patent Publication No. 4-196964 consists in that the fluctuation of the scanning speed is determined by reading the image together with an equal-pitch scale disposed in the feed direction and comparing read-time intervals of the scale lines with the known reference value. This method can improve the accuracy of image scanning to compensate the possible distortion of a reproduced image due to fluctuation of the scanning speed without a considerable increase of the manufacturing cost of the image reading device.
However, the line sensor used in the above-described device is driven by clock signals and reads a document image at a specified time-interval in synchronism with the clock signals.
Consequently, a change in the scanning speed may not be detected if the displacement due to the scanning speed change of the scanner is smaller than one pixel in the feed direction. To increase the resolving power of the line sensor for detecting the scanning speed fluctuation, it is necessary to considerably increase the clock frequency. This solution, therefore, is impractical in view of increasing high-frequency noise and additional cost.
In case of reading the reference line scale by using analog elements (photo diodes or photo transistors) in combination with a specialized A/D converter, time must be measured by using a high-speed A/D converter, a high-speed timer and a high-response optical device. This may also arise the problems of increasing high-frequency noise and increasing the cost.
Furthermore, the use of a higher frequency clock cannot always enable the line sensor to finely read the equal-pitch line scale for analysis of the speed fluctuation because the size of an image read by one pixel of the line sensor is determined by an optical lens system interposed between a document and the line sensor. Namely, the line sensor may not detect the scanning speed fluctuation if the displacement due to the fluctuation is smaller than one pixel in the feed direction.
The reference line scale used in the conventional image reading systems is an arrangement of lines alternating black (high-density part) and white (low-density part) with the same width. There may arise a problem that a half-pitch shift of the reading pitch frequency of a scanner in the feed direction from the frequency of the equal-pitch lines of the reference scale may result in outputting a halftone image which cannot be analyzed.
The use of an equal-pitch scale having lines with width not less than two pixels of the line sensor for solving the above problem may make the system unable to detect scanning speed fluctuation.
Analysis of the scanning speed fluctuation by integration of results of obtained by processing an image from its top with a comb filter may have an incorrect result if read image data contains erroneous data due to a small change in the density of the equal-pitch scale image and the presence of dust and noise when reading the image.
In addition, the above calculation premises that the same outputs appear continuously to represent black or white lines of the reference scale image. However, the black and white lines of the scale may have small fluctuation of output values in may case by the effect of adjustments of the line sensor and the A/D converter and the above-mentioned errors.
Therefore, the white line has width equal to two pixels can not always have the same values by two successive pixels at the output of the A/D converter. Speed fluctuation component cannot be separated and extracted if the two white lines of the reference scale have different output values.
The above problem may be avoided by applying a single correction factor to all image data so that all white parts and all black parts may have respective fixed values. However, this solution may cause partial excessive or insufficient compensation if a white shading level or a black shading level is preset to vary while the scanner scans image data in the feed direction. The accuracy of analysis may be decreased.
Furthermore, when the corrected values are not only used for separating a black line part from a white-line part but used for calculating the scanning speed fluctuation, the analysis may not attain the sufficient accuracy depending on the corrected state.
It can be also sought to observe the scanning speed fluctuation by extracting a two-dot part showing the same output values in series and determining a value of this position by extracting an integrated value of the part exiting ahead by two dots from the extracted output value. This method, however, has a final result of subtraction at a portion from a black-line to a white-line or at a portion from a while-line to a black-line. For white or black lines each having a width of two dots or more, final values are spaced with the white or black part width, zeroing data for each spacing.
Consequently, only a part of data obtained by processing outputs of the A/D converter with a comb filter is used and remaining data is discarded. No improvement is achieved even by holding a preceding value for each zero-data part.
In other words, the analysis with a chart having a widened frequency (e.g., black line of 1 dot in width and a white line widened to x dots in width) can effectively use only 2/(x+1) of measurement results.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a document-image reading device that can separate and extract a speed fluctuation component by determining a gray-level change of each scale line (not reading time-interval), analyze a state of speed fluctuation of scanning in the feed direction and, based on the analysis result, eliminate the possibility of image deformation that may be caused from the unstable factors of the driving mechanism of the device.
Namely, a speed fluctuation component is separately extracted by reading a change in gray level of respective scale lines and analyzed a speed fluctuation state of a scanner scanning in the feed direction and deformation of an image can be eliminated based on the analysis result.
Another object of the present invention is to provide a document-image reading device that can separately extract speed fluctuation of its scanner when working with an equal-pitch scale representing alternations of a black line of one pixel in wi
Horiuchi Takao
Morimoto Jun
Watase Shigeru
Coles Edward
Dike. Bronstein, Roberts & Cushman, IP Practice Group, Edwards &
Hartnell, III George W.
Pokrzywa Joseph R.
Sharp Kabushiki Kaisha
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