Image processing apparatus

Claim 2

An image processing apparatus comprising: inputting means for inputting pixel data; variable-threshold generating means for generating a threshold corresponding to said input pixel data; fixed-threshold generating means for generating a fixed threshold; decision means for making a decision as to whether or not an input objective pixel is located in the vicinity of an edge portion of an image; selecting means for selecting said variable-threshold generating means or said fixed-threshold generating means on the basis of the result of said decision made by said decision means; and quantizing means for quantizing said objective pixel on the basis of a threshold selected by said selecting means.

Claim 3

An image processing apparatus according to claim 1, wherein said inputting means includes means for reading an original image in units of pixels and generating digital pixel data corresponding to the individual pixels.

Claim 4

An image processing apparatus according to claim 1, wherein said pixel data is density data obtained when said original image is read.

Claim 5

An image processing apparatus according to claim 1, wherein as the value of said pixel data input from said inputting means becomes smaller, the range in which said threshold generated by said variable-threshold generating means varies becomes larger.

Claim 6

An image processing apparatus according to claim 1, wherein said threshold generated by said variable-threshold generating means varies about said fixed threshold generated by said fixed-threshold generating means.

Claim 7

An image processing apparatus according to claim 1, wherein said fixed-threshold generating means generates a threshold which takes on an approximately middle value within the range of values which can be input by said inputting means.

Claim 8

An image processing apparatus according to claim 1, further comprising: memory means for storing a predetermined number of lines of data quantized by said quantizing means and relative to pixels located in the vicinity of the position of said objective pixel; decision means for making a decision as to whether or not an output pixel dot is present in said quantized pixel data belonging to a predetermined area in the vicinity of the position of said objective pixel and stored in said memory means; and setting means for forcibly setting said pixel data processed by said quantizing means to a state wherein no output dot is present on the basis of the value of said pixel data input by said inputting means and the result of said decision made by said decision means.

Claim 9

An image processing apparatus according to claim 1, wherein said quantizing means is means for generating binarized pixel data based on an error diffusion method.

Claim 10

An image processing apparatus according to claim 8, wherein when an error occurring when said objective pixel data is quantized into a binary output data is negative and if said decision means determines that said objective pixel is located in the vicinity of an edge portion of an image, said error which has occurred is not diffused into an area corresponding to the positions of non-quantized neighboring pixels.

Claim 11

An image processing apparatus according to claim 8, wherein when an error occurring when said objective pixel data is quantized into a binary output data is negative and if said decision means determines that said objective pixel is located in the vicinity of an edge portion of an image, said error which has occurred is not diffused into an area corresponding to the positions of non-binarized pixels which are located on the side of said objective pixel which is nearer to said edge portion.

Claim 12

An image processing apparatus for generating output pixel data by quantizing input pixel data, comprising: inputting means for inputting pixel data; area-state determining means for making a decision as to the state of quantized output pixel data in an area near to an objective pixel input from said input means; edge determining means for making a decision as to whether or not said objective pixel input by said inputting means is located in the vicinity of an edge portion of an image; variable-threshold generating means for generating a threshold corresponding to said input pixel data; quantizing means for quantizing said input pixel data into output pixel data on the basis of said threshold generated by said variable-threshold generating means and the result of said decision made by said area-state determining means; and distributing means for distributing an error amount which occurs when said quantizing means effects quantization to at least one non-quantized pixel which is positioned in the vicinity of said objective pixel.

Claim 13

An image processing apparatus for generating output pixel data by quantizing input pixel data, comprising: inputting means for inputting pixel data; area-state determining means for making a decision as to the state of quantized output pixel data in an area near to an objective pixel input from said input means; edge determining means for making a decision as to whether or not said objective pixel input by said inputting means is located in the vicinity of an edge portion of an image; variable-threshold generating means for generating a threshold corresponding to said input pixel data; quantizing means for quantizing said input pixel data into output pixel data on the basis of said threshold generated by said variable-threshold generating means and the result of said decision made by said area-state determining means; and distributing means for distributing an error amount which occurs when said quantizing means effects quantization to at least one non-quantized pixel which is positioned in the vicinity of said objective pixel.

Claim 14

An image processing apparatus according to claim 11, wherein said pixel data is density data obtained when an original image is read.

Claim 15

An image processing apparatus according to claim 11, wherein said threshold generated by said variable-threshold generating means exhibits a variation for each input pixel, as the value of said input pixel data becomes smaller, the width of said variation becoming larger.

Claim 16

An image processing apparatus according to claim 11, wherein said threshold generated by said variable-threshold generating means varies about an approximately middle value within the range of values which can be input by said inputting means.

Claim 17

An image processing apparatus according to claim 11, wherein said quantizing means is binarizing means for converting objective pixel data into binary output data, said area-state determining means making a decision as to whether or not an output dot is present in a predetermined area near to said objective pixel.

Claim 18

An image processing apparatus according to claim 15, wherein when an error occurring when said objective pixel data is binarized is negative and if said objective pixel is located in the vicinity of an edge portion of an image, said distributing means distributes substantial zero to the positions of non-binarized pixels located in the vicinity of said objective pixel.

Claim 19

An image processing apparatus according to claim 15, wherein when an error occurring when said objective pixel data is binarized is negative and if said decision means determines that said objective pixel is located in the vicinity of an edge portion of an image, said distributing means distributes substantial zero to the positions of non-­binarized pixels located on the side of said objective pixel which is nearer to said edge portion.

Claim 20

An image processing apparatus according to claim 12, wherein if the density of said objective pixel is low and if said area-state determining means determines that no output dot is present in a predetermined area near to said objective pixel, said quantizing means provides output pixel data corresponding to the position of said objective pixel in the form of data including no output dot.

Claim 21

An image processing method in which an error occurring when said input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising the steps of: calculating a distance by which black pixels are allowed to be close to each other in accordance with the density of an objective pixel; determining whether or not a quantized black pixel is contained within said distance; and outputting said objective pixel as a white pixel if said quantized black pixel is contained within said distance.

Claim 22

An image processing method in which an error occurring when said input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising the steps of: calculating a distance by which black pixels are allowed to be close to each other in accordance with the density of an objective pixel; determining whether or not a quantized black pixel is contained within said distance; and outputting said objective pixel as a white pixel if said quantized black pixel is contained within said distance.

Claim 23

An image processing method in which an error occurring when said input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising the steps of: calculating the size of an area in which black pixels are allowed to be close to each other in accordance with the density of an objective pixel; determining whether or not a quantized black pixel is contained in said area; and outputting said objective pixel as a white pixel if said quantized black pixel is contained in said area.

Claim 24

An image processing method in which an error occurring when said input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising the steps of: calculating the size of an area in which black pixels are allowed to be close to each other in accordance with the density of an objective pixel; determining whether or not a quantized black pixel is contained in said area; and outputting said objective pixel as a white pixel if said quantized black pixel is contained in said area.

Claim 25

An image processing apparatus in which an error occurring when input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising: arithmetic means for calculating a distance by which black pixels are allowed to be close to each other in accordance with the density of an objective pixel; detecting means for detecting the distance between the position of said objective pixel and the position of a pixel located at the shortest distance from said objective pixel in a group of quantized black pixels; decision means for determining whether or not said distance detected by said detecting means is contained within said distance calculated by said arithmetic means; and quantization correcting means for correcting said objective pixel as a white pixel and outputting said white pixel if said decision means determines that said distance detected by said detecting means is contained within said distance calculated by said arithmetic means.

Claim 26

An image processing apparatus in which an error occurring when input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising: arithmetic means for calculating a distance by which black pixels are allowed to be close to each other in accordance with the density of an objective pixel; detecting means for detecting the distance between the position of said objective pixel and the position of a pixel located at the shortest distance from said objective pixel in a group of quantized black pixels; decision means for determining whether or not said distance detected by said detecting means is contained within said distance calculated by said arithmetic means; and quantization correcting means for correcting said objective pixel as a white pixel and outputting said white pixel if said decision means determines that said distance detected by said detecting means is contained within said distance calculated by said arithmetic means.

Claim 27

An image processing apparatus according to claim 21 in which an error occurring when input pixel data is quantized is distributed to a non-quantized neighboring pixel, wherein said quantization is binarization based on an error diffusion method.

Claim 28

An image processing apparatus in which an error occurring when input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising: first calculating means for calculating, from an error occurring during quantization, values to be distributed to respective non-quantized neighboring pixels which are located in the vicinity of an objective pixel; first distributing means for distributing said values calculated by said first calculating means to the positions of corresponding individual neighboring pixels; second calculating means for calculating a lost error amount from the total sum of said values calculated by said first calculating means; and second distributing means for distributing said error amount calculated by said first calculating means to the position of one neighboring pixel which is located in a relatively different position with respect to said objective pixel position, at least each time the position of said objective pixel is updated.

Claim 29

An image processing apparatus in which an error occurring when input pixel data is quantized is distributed to a non-quantized neighboring pixel, comprising: first calculating means for calculating, from an error occurring during quantization, values to be distributed to respective non-quantized neighboring pixels which are located in the vicinity of an objective pixel; first distributing means for distributing said values calculated by said first calculating means to the positions of corresponding individual neighboring pixels; second calculating means for calculating a lost error amount from the total sum of said values calculated by said first calculating means; and second distributing means for distributing said error amount calculated by said first calculating means to the position of one neighboring pixel which is located in a relatively different position with respect to said objective pixel position, at least each time the position of said objective pixel is updated.

Claim 30

An image processing apparatus according to claim 23, wherein said second calculating means calculates the total of the values which are below the decimal points of said respective values to be distributed.

Claim 31

An image processing apparatus according to claim 23, wherein a pixel position to which said error amount is to be distributed by said second distributing means is calculated from the address of the position of said objective pixel.

Claim 32

An image processing apparatus according to claim 23, wherein a pixel position to which said error amount is to be distributed by said second distributing means is calculated with a random number.