Method of scaling an image capable of line width preservation

• US 5,539,534 A
• Filed: 06/01/1993
• Issued: 07/23/1996
• Est. Priority Date: 06/03/1992
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Hino, Masatoshi, Munemasa, Narihiro
• Primary Examiner(s): Rogers, Scott A.
• Assistant Examiner(s): LEE, TOMMY D
• Application Number:
  US08/069,865
• Time in Patent Office: 1,148 Days
• Field of Search: 358/443, 358/445, 358/447, 358/448, 358/451, 358/452, 382/47, 382/276, 382/298, 382/299, 382/300, 382/293, 395/139
• US Class Current: 358/452
• CPC Class Codes: G06T 3/40 Scaling of whole images or parts thereof, e.g. expanding or contracting

Abstract

In scaling an image, a projected position is corrected in accordance with pixel values of original pixels surrounding a projected position where a pixel of a scaled image is projected onto an original image, and a pixel value of a pixel of a scaled image is determined in accordance with pixel values of original pixels surrounding a projected position after correction. Further, when a pixel of an original image is processed with a pixel run as a unit, coordinates of an end pixel of a pixel run in a scaled image are corrected based on the width of the pixel run and a scale factor.

Claims

1. A method of scaling a first image to obtain a second image, comprising the steps of:

scaling the first image to obtain an intermediate image;

projecting pixels of the intermediate image onto the first image to provide projected positions for second image pixels;

determining a positional correction amount for each of said projected positions from a pixel value of at least one of pixels of the first image near the projected position;

correcting each projected position by its corresponding determined correction amount; and

determining a pixel value of each second image pixel from a pixel value of a first image pixel near the projected position after correction.

2. A method according to claim 1, wherein the first image is a binary image, and determination of said positional correction amount is effected by moving a particular projected position such that a distance between said particular projected position and a boundary between a white area and a black area on said first image is constant, said particular projected position being one of said projected positions nearest to said boundary between white and black areas among projected positions in the black area of the first image, said boundary being determined by positional relations among white pixels and black pixels of the first image.

3. A method of scaling a first image having a plurality of pixel runs to a obtain a second image having a plurality of pixel runs, comprising the steps of:

obtaining, in a row direction and a column direction, first scaled boundary coordinates for a second image between first end pixels of pixel runs and second end pixels of pixel runs of different pixel values neighboring thereto by multiplying first boundary coordinates in a first image between first end pixels of pixel runs and second end pixels of pixel runs of different pixel values neighboring thereto by row direction and column direction scale factors;

obtaining scaled widths by multiplying row direction and column direction widths of the pixel runs in said first image by said row direction and column direction scale factors;

obtaining second scaled boundary coordinates for the second image between second end pixels of pixel runs and first end pixels of pixel runs of different pixel values neighboring thereto by adding values of said scaled widths to said first scaled boundary coordinates for the second image; and

obtaining coordinates of the first end pixels and the second end pixels of the pixel runs of the second image from said scaled first boundary coordinates and scaled second boundary coordinates.

4. A method of scaling a first image having black and white pixels located on points of a first scale lattice to obtain a second image having black and white pixels located on points of a second scale lattice, the black pixels and white pixels of the first image forming at least one black area and at least one white area, respectively, the method comprising:

projecting the second scale lattice onto the first scale lattice to determine four reference lattice points surrounding, in the first scale lattice, a projected position of each pixel of the second image on one of points of the second scale lattice;

finding, in each of the black areas of the first image, a foremost projected position of a second image pixel which projected position is not outside said black area and is closest to one of outermost pixels in said black area of the first image;

determining a second image pixel having said foremost projected position to be a black pixel;

displacing said foremost projected position, found in each of said black areas of the first image, by a positional correction distance to a corrected projected position such that a predetermined distance is established between an intermediate point between said black area and a white area neighboring thereto and said corrected projected position in said first image, and displacing other projected positions of pixels of the second image by said positional correction distance to their corrected projected positions; and

determining a pixel value of each of second image pixels having said other projected positions displaced to their corrected projected positions, by reference to at least one of four reference lattice points surrounding, in the first scale lattice, the corrected projected position of said each pixel.

5. A method of scaling a first image having black and white pixels defined by first scale coordinates to obtain a second image having black and white pixels defined by second scale coordinate with first and second scaling factors in row and column directions, runs of black pixels and runs of white pixels of the first image forming at least one black area and at least one white area, respectively, each of said black pixel runs having first and second end pixels and a width continuing from said first end pixel to said second end pixel, the method comprising:

determining a second scale row direction coordinate of a first end pixel of a black pixel run in the first image in accordance with said first scaling factor, said determined second scale row direction coordinate of the first end pixel run having a first integer value;

multiplying a width of said black pixel run by said first scaling factor to provide a first pixel run width product and converting said first pixel run width product to a second integer value thereby obtaining an integer value scaled width;

adding said integer value scaled width to said second scale row direction coordinate of the first end pixel of said black pixel run having said second integer value to obtain second scale row direction coordinate of a second end pixel of said black pixel run, thereby scaling said black pixel run in said row direction;

storing, in a rectangle information table, information on a first scale column direction coordinate of the first end pixel and said second scale row direction coordinates of the first and second end pixels of the black pixel run scaled in said row direction;

recognizing all black pixel runs, scaled with said first scaling factor, that are located to consecutively neighbor the first-mentioned black pixel run scaled with said first scaling factor and have the same width as that of the first-mentioned black pixel run by use of said information stored in said rectangle information table to thereby find a first scale column direction coordinate of a black pixel run located farthest from the first-mentioned black pixel run among said neighboring black pixel runs;

determining a second scale column direction coordinate of said first end pixel of the first-mentioned black pixel run in accordance with said second scaling factor, said determined second scale column direction coordinate of said first end pixel of the first-mentioned black pixel run having a third integer value;

multiplying a length from said first scale column direction coordinate of the first end pixel of the first-mentioned black pixel run stored in said rectangle information table to said first scale column direction coordinate of said farthest black pixel run by said second scaling factor to provide a second pixel run width product and converting said second pixel run width product to a fourth integer value thereby obtaining an integer scaled length; and

adding said integer scaled length to said second scale column direction coordinate of the first-mentioned black pixel run having said third integer value, to obtain a second scale column direction coordinate of said farthest black pixel run, thereby scaling the first-mentioned black pixel run and said black pixel runs consecutively neighboring thereto in said column direction to provide information on a scaled rectangle representative of the first-mentioned black pixel run and said black pixel runs consecutively neighboring thereto in said column direction.

6. A method of scaling a first image having a plurality of pixel runs each having predetermined pixel values to obtain a second image having a plurality of pixel runs, comprising the steps of:

obtaining second image coordinates of a first end pixel of pixel runs by multiplying values of first image coordinates of said first end pixel of the pixel runs in a row direction and a column direction by row direction and column direction scale factors to provide respective coordinate products and by converting said coordinate products to integer values for said second image coordinates of the first end pixel of the pixel runs;

obtaining row direction and column direction scaled widths by multiplying row direction and column direction widths of first image pixel runs by the scale factors to provide respective pixel run width products and by converting said pixel run width products to integer values for said scaled widths; and

obtaining second image coordinates of second end pixels of pixel runs by adding the integer valued scaled widths to the second image integer valued coordinates of said first end pixel of the pixel runs; and

wherein

pixel runs in said first image are scaled in one of said row and column directions on a row-by-row base or on a column-by-column directions on a row-by-row base or on a column-by-column base, comprising the steps of,

a) recording, in a rectangle information table, a second image pixel run produced by scaling a first image pixel run in said one direction,

b) comparing a next second image pixel run, produced by similarly scaled, with said recorded second image pixel run to determine whether or not said next second image pixel run has a first run portion which connects with said recorded second image pixel run as viewed in the other of said directions, whether or not said next second image pixel run has a second run portion which does not connect with said recorded second image pixel run as viewed in said one direction, and whether or not said recorded second pixel run has a portion which does not connect with said subsequent second pixel run as viewed in said other direction,

c) processing said next second image pixel run and said rectangle information table in such a manner that said first run portion of the subsequent second pixel run, when detected by said comparison, is recorded as a continuation of said recorded second image pixel run in said rectangle information table, said second run portion of the subsequent second pixel run, when detected by said comparison, is newly entered in said rectangle information table, and said portion of the recorded second pixel run which does not connect with said subsequent second pixel run when detected by said comparison, is scaled in the other direction to form information on a rectangle,

d) generating information in said portion of the recorded second pixel run which does not connect with said subsequent second pixel run and which has been scaled in both of said directions, and

e) repeating said steps a) to d) for each of the second image pixel runs.

7. A method according to claim 6, wherein:

in lieu of generating information related to a rectangle scaled in a row direction and a column direction, coordinates of vertices of the rectangle are recorded in an output table; and

a scaled image is generated row by row based on coordinates of first and second end pixels of scaled pixel runs recorded in said output table at a point of time when scaling process is brought to an end on the whole of the first image.

8. A method according to claim 6, wherein:

in lieu of generating information related to a rectangle scaled in a row direction and a column direction, coordinates of vertices of the rectangle are recorded in an output table; and

pixel runs of the second image are generated with respect to one of the row and the column thereof using said output table and rectangle information table every time when the process of one of one row portion and one column portion of the first image is terminated.

9. An image scaling system comprising:

means for receiving pixels representative of a first image;

means for receiving pixels representative of a second image, which second image is a scaled representation of the first image;

means for scaling the first image to obtain an intermediate image;

means for projecting pixels of the intermediate image onto the first image to provide projected positions for second image pixels;

means for determining a positional correction amount for each projected positions from a pixel value of at least one of pixels of the first image near the projected position;

means for correcting each projected position by its corresponding determined correction amount; and

means for determining a pixel value of each second image pixel from a pixel value of a first image pixel near the projected position after correction.