# US 5,351,137 A · Pixel density converting apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,351,137 A - Document ID: US5351137A - Status: Granted - Kind: A - Application number: 08/159,206 - Filed: 1993-11-30 - Granted: 1994-09-27 - Earliest claimed: 1989-03-14 - Assignees: Canon Kabushiki Kaisha - Inventors: Masami Kato; Takao Kato; Yasunori Hashimoto - Web page: https://patentgrep.com/patent/US5351137A ## CPC - H04N 1/40075: {Descreening, i.e. converting a halftone signal into a corresponding continuous-tone signal; Rescreening, i.e. combined descreening and halftoning} - H04N 1/40062: {Discrimination between different image types, e.g. two-tone, continuous tone} - H04N 1/40068: {Modification of image resolution, i.e. determining the values of picture elements at new relative positions (H04N1/3935 takes precedence)} - H04N 1/4052: {by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions} - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract In a pixel density converting apparatus according to the present invention, a pixel density conversion element for converting a pixel density by a factor of an arbitrary value, such as an element of the projection method or the linear interpolation method, a pixel density conversion element for increasing or decreasing a pixel density by a factor of an integer, such as an element of the majority or logical OR method, and a binarization element for conducting binarization while correcting quantizing errors, such as an element of the error diffusion method or the average error minimizing method, are combined with each other with the advantages and disadvantages of the respective elements taken into consideration, so as to achieve excellent conversion whether or not the image on which pixel density conversion is conducted or an image area is a pseudo half-tone processed image. In consequence, excellent pixel density conversion is achieved on a binary image in which a pseudo half-tone processed image and characters or line drawings are present in a mixed state. ## Claims ### Claim 1 A pixel density converting apparatus for converting a pixel density of a binary image in which a pseudo half-tone processed image and characters or line drawings are present in a mixed state, comprising: a converted pixel operation means for operating a tone or luminance of a converted pixel from a tone or luminance of a predetermined original pixel in said binary image and a positional relation between said original pixel and said converted pixel; and a binarization means for binarizing the tone or luminance of said converted pixel which is the operation results while correcting a quantizing error generated when surrounding pixels have been binarized. ### Claim 2 (depends on 1) A pixel density converting apparatus according to claim 1, wherein said binarization means corrects the quantizing error by the error diffusion method. ### Claim 3 (depends on 1) A pixel density converting apparatus according to claim 1, wherein said binarization means corrects the quantizing error by the average error minimizing method. ### Claim 4 (depends on 1) A pixel density converting apparatus according to claim 1, further comprising a threshold level setting means for setting a threshold level used for binarization by said binarization means in accordance with a conversion factor. ### Claim 5 (depends on 1) A pixel density converting apparatus according to claim 1, wherein said converted pixel operation means operates the converted pixel by the projection method. ### Claim 6 (depends on 1) A pixel density converting apparatus according to claim 1, wherein said converted pixel operation means operates the converted pixel by the linear interpolation method. ### Claim 7 (depends on 1) A pixel density converting apparatus according to claim 1, further comprising a integral conversion means for increasing or decreasing the pixel density by a factor of an integer, and a conversion factor setting means for setting a factor for said converted pixel operation means and that for said integral conversion means in accordance with a conversion factor. ### Claim 8 (depends on 7) A pixel density converting apparatus according to claim 7, wherein said integral conversion means performs a conversion by the thinning out process. ### Claim 9 (depends on 7) A pixel density converting apparatus according to claim 7, wherein said integral conversion means performs a conversion by the majority process. ### Claim 10 (depends on 7) A pixel density converting apparatus according to claim 7, wherein said integral conversion means performs a conversion by the averaging process. ### Claim 11 (depends on 7) A pixel density converting apparatus according to claim 7, wherein said integral conversion means performs a conversion by the logical OR process. ### Claim 12 (depends on 1) A pixel density converting apparatus according to claim 1, further comprising a plurality of integral conversion means for increasing or decreasing the pixel density by a factor of an integer, an integral conversion means selection means for selecting either of said plurality of integral conversion means on the basis of determination as to whether or not an image area is a pseudo half-tone processed area, and a conversion factor setting means for setting a factor for said converted pixel operation means and that for said integral conversion means in accordance with a conversion factor. ### Claim 13 (depends on 12) A pixel density converting apparatus according to claim 12, wherein said plurality of integral conversion means is a combination of a conversion means for conducting the thinning out process and a conversion means for conducting the majority process, and wherein the psuedo half-tone processed image area is processed by the thinning out method. ### Claim 14 (depends on 12) A pixel density converting apparatus according to claim 12, wherein said plurality of integral conversion means is a combination of a conversion means for conducting the thinning out process and a conversion means for conducting the averaging process, and wherein the psuedo half-tone processed image area is processed by the thinning out method. ### Claim 15 (depends on 12) A pixel density converting apparatus according to claim 12, wherein said plurality of integral conversion means is a combination of a conversion means for conducting the thinning out process and a conversion means for conducting the logical OR process, and wherein the psuedo half-tone processed image area is processed by the thinning out method. ### Claim 16 (depends on 1) A pixel density converting apparatus according to claim 1, further comprising an edge emphasis means which is interposed between said converted pixel operation means and said binarization means. ### Claim 17 A pixel density converting apparatus for a binary image which employs the linear interpolation method, comprising: a pixel taking out means for taking out 4 original pixels surrounding a converted pixel on a projection surface formed by projecting a converted image onto an original image; a position operation means for operating a position of said converted pixel relative to said four original pixels; an area determination means for determining a predetermined area from said relative position obtained; and a converted pixel determination means for determining a value of said converted pixel from a logical expression determined by said determined area. ### Claim 18 A pixel density converting apparatus for increasing or decreasing a number of pixels of a binary image by means of the projection means, comprising: an operation means for operating a tone or luminance of a converted pixel by limiting the number of pixels to be referred to which are to be subjected to conversion and which corresponds to 1 pixel obtained by the projecting method to a predetermined value and for approximating a tone of a pixel other than said limited pixels by tones of the adjacent reference pixels. ### Claim 19 A pixel density converting apparatus for increasing or decreasing a number of pixels of a binary image by means of the projection means, comprising: an operation means for operating a tone or luminance of an objective pixel on the basis of overlapping of referred pixels on a pixel converted by the projection method whose one side has a length which is an integral power of 2. ### Claim 20 A pixel density converting apparatus for converting a pixel density of binary image, comprising: an operation means for operating a tone or luminance of a pixel to be converted and converting a pixel density; a threshold level setting means for setting a threshold level used for binarization of the tone or luminance of a pixel in accordance with a conversion factor; and a binarization means for binarizing the tone or luminance of the converted pixel by the comparison results of the threshold level and the tone or luminance of the converted pixel. ### Claim 21 (depends on 20) A pixel density converting apparatus according to claim 20, wherein said operation means operates the tone or luminance of the pixel to be converted by the projection method. ### Claim 22 (depends on 20) A pixel density converting apparatus according to claim 20, wherein said operation means operates the tone or luminance of the pixel to be converted by the interpolation method. ### Claim 23 A pixel density converting apparatus for converting a pixel density of binary image by a desired conversion factor, comprising: an operation means for operating an average tone or luminance of a pixel to be converted by the projection method; an edge emphasis means for emphasizing an edge of the image data converted by said operation means as multi-level image data; and a binarization means for binarizing the image data emphasized by said edge emphasis means. ### Claim 24 A pixel density converting apparatus for converting a pixel of a binary image in accordance with the increase or decrease of the number of pixels, comprising: first conversion means for conducting a conversion process by the projection method; and second conversion means for changing the number of pixels by a predetermined amount of pixels. ### Claim 25 (depends on 24) A pixel density converting apparatus according to claim 24, wherein said second conversion means changes the number of pixels by a thinning out process. ### Claim 26 (depends on 24) A pixel density converting apparatus according to claim 24, wherein said second conversion means changes the number of pixels by an averaging process. ### Claim 27 (depends on 24) A pixel density converting apparatus according to claim 24, wherein said second conversion means changes the number of pixels by a majority process.