Image analysis – Image transformation or preprocessing – Changing the image coordinates
Reexamination Certificate
1998-09-28
2001-07-17
Couso, Yon J. (Department: 2623)
Image analysis
Image transformation or preprocessing
Changing the image coordinates
Reexamination Certificate
active
06263120
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image-data interpolation processing method for interpolation of insufficient image data to achieve high-resolution transformation and magnification of a multigradational image containing different kinds of components coexisting in the image.
A typical image-processing device for processing an image data inputted from a scanner or the like input device usually conducts interpolation of insufficient image data to convert a low-resolution multigradational image into a high-resolution and/or an enlarged small-sized multigradational image. There are several known methods for interpolating image data. Examples are nearest neighbor interpolation that directly applies data of the nearest neighbor to a pixel to be interpolated, bilinear interpolation that calculates a planar product-sum from surrounding pixels and cubic convolution interpolation that calculates a curved-surface product-sum according to the surrounding pixels.
These interpolation processing methods have both merits and demerits. The nearest neighbor interpolation has the shortest processing time but produces jaggies of an oblique line, resulting in deterioration of the image. The bilinear interpolation has a relatively short processing time and suitable to interpolate a portion having a smooth change in density, but it causes unclearness of a portion sharply changing in density such as an edge of the image. The cubic convolution interpolation can smoothly interpolate a portion having a moderate change in density with a small deterioration of the image quality and clearly reproduce an edge portion but it requires a long time of processing and emphasizes a noise existing in a smooth density-varying portion, resulting in the deterioration of the image quality.
Consequently, an image that includes a character (edge-like) image area and photographic (non-edge) image area cannot sufficiently be processed by applying merely one of the above methods of interpolation. In other words, any of the above interpolation methods cannot convert and/or enlarge the image in such a way that it may realize at the same time the high-resolution of the character-image area and the smoothly varying density of the photographic image area.
Accordingly, an attempt has been made to provide an image processing device that strictly distinguishes an edge-component area from an edgeless area and processes these different areas by different methods of interpolation. For example, Japanese Laid-Open Patent Publication No. 5-135165 discloses such an arrangement that determines the maximum value and the minimum value of densities in a local area including attentional pixel and surrounding pixels, discriminates, based on the maximal density value obtained by subtracting the least value from the largest value, whether the attentional pixel belongs to the character (edge) area or the (non-edge) face-area, and executes processing adapted to the character image area or the photographic image area.
However, the image processing device disclosed in Japanese Laid-Open Patent Publication No. 5-135165, which extracts an edge image area according to a change in density of pixels including an attentional pixel, involves following problems:
The device may obtain an erroneous large differential density value from a partial image area containing a noise irrespective of the area having a moderate variation of densities of pixels including an attentional pixel.
Furthermore, the rotation of a whole image may cause a change in a density pattern of the partial image area due to the changed direction of the edge image. In other words, the same partial image area extracted in different directions may have two different discrimination results. To avoid this, different extracting conditions must be provided for the image before and after rotated, whereby the discrimination processing may be complicated.
In addition, image areas must be separated before interpolation, whereby the processing not only takes longer time but also complicates the circuitry of the device which, therefore, has an enlarged size and is expensive to manufacture.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image-data interpolation processing method that can easily process an image including different kinds of image areas (e.g., a character image area and a photographic-image area) through performing adaptive interpolation to create the high-resolution character image-area and the smooth gradational photographic image area with no need of separation of areas before interpolation, thus enabling an image processing device to be compact in size with simplified circuitry and manufactured at a reduced cost.
Another object of the present invention is to provide an image-data interpolation processing method that can extract a partial image area from an original image, divide a frequency-conversion coefficient matrix, for converting image data composing the partial image extracted from an original image into frequency data, into a matrix of plural frequency domains, discriminate whether the partial image contains an edge-portion according to a mean value obtained for each frequency domain and select a suitable interpolating method in such away the partial image including an edge portion is processed by cubic convolution interpolation for maintaining the edge-portion feature and the partial image not including an edge-portion is processed by bilinear interpolation for maintaining the smooth change in density.
Another object of the present invention is to provide an image-data interpolation processing method that can extract a partial image area from an original image, convert image data composing the partial image extracted from an original image into frequency data by discrete cosine transformation processing, divide discrete-cosine transformation coefficients into plural frequency domains according to coordinates in a matrix, discriminate whether the area contains an edge-portion according to a mean value obtained for the domain and select a suitable interpolating method, whereby the discrete cosine transformation of image data can be easily done and the discrimination of edge-portion can be done without consideration of direction of the edge portion.
Another object of the present invention is to provide an image-data interpolation processing method that can calculate mean values of frequency conversion coefficients for each of the frequency domains by using absolute values of the coefficients, whereby a sum of the frequency conversion coefficients for respective frequency domains can be calculated without canceling the features of respective pixels, thus allowing the interpolated image to maintain the features of the original.
Another object of the present invention is to provide an image-data interpolation processing method that can execute adaptive processing of partial images of an original image depending on the presence or absence of an edge-like component therein in such a manner that a partial image containing an edge component is processed by cubic convolution interpolation for maintaining the edge image feature or a partial image with no edge-like component is processed by bilinear interpolation for maintaining smooth change in density of pixels therein.
Another object of the present invention is to provide an image-data interpolation processing method that can determine the density of an interpolating pixel by using a monotone increasing function allowing replacing a gradient and an input value depending on a difference between densities of two neighbors existing one at each side of the interpolating pixel in each partial image, whereby any partial image can be adaptively processed with ease for a shorter time, eliminating the need of discriminating whether the image contains an edge-like component or not.
Another object of the present invention is to provide an image-data interpolation processing method that can interpolate an image data by presetting an interpolating pixel value at a half of a differential d
Couso Yon J.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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