Image analysis – Image compression or coding – Gray level to binary coding
Reexamination Certificate
1997-04-01
2001-09-04
Boudreau, Leo (Department: 2621)
Image analysis
Image compression or coding
Gray level to binary coding
C382S298000, C358S451000
Reexamination Certificate
active
06285792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image retrieval device for optically retrieving an image and obtaining binary image data of the image.
2. Description of the Related Art
An image scanners using a charge couple device (CCD) sensor or a contact type image sensor are examples of image retrieval devices for obtaining binary data or multi-valued digital image data by optically retrieving an image. Recently, to answer demands for ever increasingly higher resolution, a 12 dot/mm or 16 dot/mm resolution image scanner has been developed.
However, the resolution of retrieval portions used in facsimile machines is set based on a transmission standard of 8 dot/mm. In the United States, the relative standard is defined by the Federal Communications Commission (FCC) Part 68, RS-470. In Japan, the relative standard is defined by the International Telegraph and Telephone Consultative Committee (CCITT). Therefore, when a high resolution image scanner is used as an image retrieval portion of a facsimile machine, there is a need to reduce the number of pixels representing the image. However, it is very difficult to reduce the number of pixels while the image is still in its optical form.
Therefore, in conventional image retrieval devices, pixels of the analog image signal are first converted into binary or multi-valued digital image data. Then, the image pixels are thinned at a predetermined rate to change the total number of the pixels. For example, when an image is retrieved at a resolution of 12 dot/mm, then by thinning the number of pixels down to two thirds of the original total retrieved, the image can be converted into the reduced resolution of 8 dot/mm. Similarly, when the image is retrieved at a resolution of 16 dot/mm, then by reducing thinning the number of pixels down to half the original total retrieved, then the required resolution of 8 dot/mm can be obtained.
SUMMARY OF THE INVENTION
In the above-described conventional image retrieval device, a great deal of information is lost because the number of pixels is reduced by thinning pixels. For example, when an image signal of an original image retrieved at the resolution of 16 dot/mm is converted to obtain binary image data, wherein each pixel is represented by a binary value, then one out of every two pixels is thinned to obtain the resolution of 8 dot/mm. Because only half the original pixels remain, the resultant data representing the image will contain information on only half the original image, that is, as if only half the image was retrieved. Because such a great deal of information on the original image is lost, the quality of the printed image will be poor. When the image data is converted into binary data and processed using dithering processes, then moir{acute over (e )} can be generated in the resultant image.
It is an objective of the present invention to overcome the above-described problems and to provide an image retrieval device capable of reducing the amount of image information lost when the number of pixels is converted.
In order to achieve the above-described objectives, an image retrieval device according to the present invention includes: an image retrieval unit for optically retrieving an image and outputting an analog image signal according to the image; an analog-to-digital conversion unit for converting the image signal from the image retrieval unit into multi-valued data for a number of pixels representing the image; and a pixel number conversion unit for reducing the number of pixels in the multi-valued data from the analog-to-digital converter by combining multi-valued data for predetermined pluralities of the number of pixels into multi-valued data for single pixels.
With this configuration, the image data is converted into binary data after the number of pixels is reduced by combining certain pluralities of pixels of multi-valued data into single pixels of multi-valued data. As a result, less information on the original image is lost when converting the number of pixels. Accordingly, degradation in quality of printed images, caused by conversion of the number of pixels, can be reduced.
Explained in more detail, the analog-to-digital converter converts the analog signal into multi-valued digital data. Each set of the multi-valued digital data has two or more bits. When the number of pixels in one single line is to be reduced to two thirds the original number, then the pixel number conversion unit treats each set of three consecutive pixels as one group. Of the three pixels, the pixel number conversion unit combines two adjacent pixels, serving as a predetermined plurality in this case, into a single pixel. As a result, three pixels are converted into two pixels. This process is repeated in each group of three pixels.
On the other hand, when every two pixels are to be combined into a single pixel, then a pixel number conversion unit calculates the average value of the multi-valued data for each set of two pixels. When the pixel number conversion unit obtains a single pixel's worth of multi-valued data by calculating the average value of more than one pixel's worth multi-valued data, then the number of pixels can be converted using a simple calculation that will not result in loss of information from the original image.
Combination of two pixels into a single pixel can be achieved by calculations other than averaging. For example, a calculation method can be use wherein the average value of one set of pixels can have an effect on the multi-valued data for surrounding pixels. The image retrieval unit can be a CCD sensor, a contact type image sensor, or some other commonly used device. A variety of analog-to-digital converters are also available.
According to another aspect of the present invention, a binarization unit is provided for converting multi-valued data from the pixel number conversion unit into binary image data for each pixel. In this case, the image data can be converted into binary data, which is commonly used in image devices. Furthermore, moiré, caused by loss of information when image data is processed by dithering processes, can be prevented.
According to another aspect of the present invention, a selection unit is provided for selectively, that is, according to a selection signal inputted from an external source, outputting one of either the multi-valued data from the analog-to-digital conversion unit or the multi-valued data from the pixel number conversion unit. With this configuration, the resolution of the resultant image data can be optionally selected. Such a function is very convenient when a facsimile machine to which the present invention is applied is used as an image scanner or a copy machine. That is, when the facsimile machine according to the present invention is used as an image scanner or as a copy machine, then the resolution can be set to a high resolution. On the other hand, when the facsimile device is used for transmitting images to a remote facsimile machine, then the resolution can be set to a low resolution. Therefore, the facsimile machine can function as a high quality image scanner or a copy machine and also as a facsimile machine which follows transmission standards.
The selection signal can be generated by a user directly manipulating a key or can be automatically generated when a key is manipulated for selecting a certain operation mode. For example, when the facsimile machine is used as a facsimile machine, the selection signal can be generated by the user manipulating a key for selecting the resolution. Alternatively, the selection signal can be automatically generated when the user manipulates a key for selecting the facsimile transmission function or the copy function of the facsimile machine.
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patent
Boudreau Leo
Brother Kabushiki Kaisha
Oliff & Berridg,e PLC
Sherali Ishrat
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