Image processor and image processing method handling multilevel image data

• US 6,292,268 B1
• Filed: 09/01/1998
• Issued: 09/18/2001
• Est. Priority Date: 09/04/1997
• Status: Expired due to Term

• Current Assignee: Minolta Co., Ltd. (Konica Minolta Inc.)
• Original Assignee: Minolta Co., Ltd. (Konica Minolta Inc.)
• Inventors: Hirota, Soh, Tada, Kaoru, Ishiguro, Kazuhiro
• Primary Examiner(s): LEE, TOMMY D
• Application Number:
  US09/144,466
• Time in Patent Office: 1,113 Days
• Field of Search: 382/251, 382/252, 382/237, 382/270, 358/455, 358/456, 358/1.9
• US Class Current: 358/3.03
• CPC Class Codes: H04N 1/4052 by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions

Abstract

An image processor converts pixel data represented with m gradations into pixel data represented with n gradations by using the error diffusion method. The m and n are both given integers and satisfy 2<n<m. Not only the error but also a weight assigning value is added to pixel data to be converted. The weight assigning value is determined according to the values of m and n.

Claims

1. An image processor comprising:

a gradation converter for converting pixel data represented with m gradations into pixel data represented with n gradations;

an error calculation circuit for calculating an error generated by the conversion of said gradation converter;

an error diffusing circuit for diffusing the error calculated by said error calculation circuit to peripheral pixels situated on the periphery of a target pixel;

a selecting unit for selecting a data processing mode; and

an weight assigning circuit for adding a weight assigning value corresponding to the data processing mode selected by the selecting unit to the pixel data of the peripheral pixel to be converted; and

wherein m and n are both given integers and satisfy 2<

n <

m and the weight assigning value added by the weight assigning circuit is decided in accordance with the value of n.

2. The image processor as claimed in claim 1, wherein said gradation converter includes a converter for comparing pixel data of the target pixel with a predetermined threshold value.

3. The image processor as claimed in claim 1, wherein said an error calculation circuit includes a subtracter for calculating an error between the pixel data having been converted by said converter and pixel data before the conversion.

4. The image processor as claimed in claim 1, wherein said error diffusing circuit includes an error memory for assigning the error to the peripheral pixels.

5. The image processor as claimed in claim 1, wherein said weight assigning circuit includes a plurality of weight assigning matrices and a selector for selecting one from said weight assigning matrixes according to the processing mode selected by the selecting unit.

6. An image processor comprising:

a gradation converter for converting pixel data represented with m gradations into pixel data represented with n gradations;

an error calculation circuit for calculating an error generated by the conversion of said gradation converter;

an error diffusing circuit for diffusing the error calculated by said error calculation circuit to peripheral pixels situated on the periphery of a target pixel;

a selecting unit for selecting a data processing mode; and

an weight assigning circuit for adding a weight assigning value corresponding to the data processing mode selected by the selecting unit to the pixel data of the peripheral pixel to be converted; and

wherein m and n are both given integers and satisfy 2<

n <

m,

wherein said weight assigning circuit includes a plurality of weight assigning matrices and a selector for selecting one from said weight assigning matrices according to the processing mode selected by the selecting unit, wherein said weight assigning circuit further includes a weight correction circuit for correcting the weight assigning value according to the value of m and n.

7. An image processor comprising:

a gradation converter for converting pixel data represented with m gradations into pixel data represented with n gradations, wherein m and n are both given integers and satisfy 2<

n<

m;

an error calculation circuit for calculating an error generated by the conversion of said gradation converter;

an error diffusing circuit for diffusing the error calculated by said error calculation circuit to peripheral pixels situated on the periphery of a target pixel; and

an weight assigning circuit for adding a weight assigning value decided according to the value of the n to the pixel data of the peripheral pixel to be converted.

8. The image processor as claimed in claim 7, wherein said gradation converter includes a converter for comparing pixel data of the target pixel with a predetermined threshold value.

9. The image processor as claimed in claim 7, wherein said an error calculation circuit includes a subtracter for calculating an error between the pixel data having been converted by said converter and pixel data before the conversion.

10. The image processor as claimed in claim 7, wherein said error diffusing circuit includes an error memory for assigning the error to the peripheral pixels.

11. The image processor as claimed in claim 7, wherein said weight assigning circuit includes a plurality of weight assigning matrices and a selector for selecting one from said weight assigning matrixes.

12. An image processing method comprising steps of:

converting pixel data represented with m gradations into pixel data represented with n gradations;

calculating an error generated by the conversion of said converting step;

diffusing the calculated to peripheral pixels situated on the periphery of a target pixel;

selecting a data processing mode; and

adding a weight assigning value corresponding to the selected data processing mode to the pixel data of the peripheral pixel to be converted; and

wherein m an n are both given integers and satisfy 2<

n <

m,

wherein the weight assigning value added in said adding step is decided in accordance with the value of n.

13. An image processing method comprising steps of:

converting pixel data represented with m gradations into pixel data represented with n gradations, wherein m and n are both given integers and satisfy 2<

n<

m;

calculating an error generated by the conversion of said converting step;

diffusing the calculated error to peripheral pixels situated on the periphery of a target pixel; and

adding a weight assigning value decided according to the value of n to the pixel data of the peripheral pixel to be converted.