US 5,479,538 AGranted

Error diffusing method in image reproducing process and image processing apparatus using such a method

AssigneeNippon Steel Corporation

InventorYasuhiko Takahashi

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Abstract

An error diffusing method and apparatus are used for an image processing in which a tone of each of the pixels of the image is approximated by either a maximum or minimum tone determined from the tone value of that pixel. The pixels are processed sequentially in a predetermined order and either a first code indicative of the maximum tone or a second code indicative of the minimum tone, depending on a magnitude of the tone of the pixel, is allotted to each of the pixels. An error obtained as a difference between the tone value of that pixel and the code allotted thereto is a negative error when the first code is allotted thereto and a positive error when the second code is allotted. When the error is positive it is diffused to the selected adjacent pixels to correct their tone values by predetermined proportions of the error, and when the error is negative, the tone value of each of the selected adjacent pixels is maintained without correction or replaced by a predetermined proportion of the error based on the relationship between the absolute value of the predetermined proportion of the error and the absolute value of the tone value of the pixel, wherein allotting of one of the codes to each pixel is based on the tone value of the pixel corrected by the error diffused from the selected adjacent pixels.

Claims10

Dependent claims

An error diffusing method in an image reproducing process wherein an image is reproduced by approximating a tone of each of a plurality of pixels constituting the image by either a maximum tone or a minimum tone, said method comprising:

1) sequentially processing the pixels in a predetermined order to allocate to each of the pixels one of a first code indicative of a tone value of the maximum tone and a second code indicative of a tone value of the minimum tone which is determined depending on an actual tone of the one pixel;
2) calculating an error as a difference between the actual tone of the one pixel and the tone value indicated by the code allocated to the one pixel and setting the error as a negative error when the first code is allocated to the one pixel and as a positive error when the second code is allocated to the one pixel;
3) diffusing the calculated error to each of a plurality of the following adjacent pixels, which are located in predetermined positional relationships with the one pixel and are to be processed after the one pixel has been processed, thereby correcting the tone value of each of the following adjacent pixels, so that when the calculated error is the positive error, the tone value of each of the following adjacent pixels is corrected by adding thereto a predetermined proportion of the positive error, and when the calculated error is the negative error, an absolute value of the predetermined proportion of the negative error is compared with an absolute value of the tone value of each of the following adjacent pixels and when the former is larger than the latter, the tone value of each of the following adjacent pixels is replaced by the predetermined proportion of the negative error and when the former is no larger than the latter, the tone value of each of the following adjacent pixels is maintained;
and
4) correcting the tone value of the one pixel prior to applying the processing step to the one pixel, when there exists at least one preceding adjacent pixel which should be processed before the one pixel is processed and whose error should be diffused to the one pixel, by the error diffused from the one preceding adjacent pixel.

2 more elements

An image processing apparatus comprising:

1) means for processing a plurality of pixels constituting an image in a predetermined order to allocate to each of the plurality of pixels one of a first code indicative of a tone value of a maximum tone and a second code indicative of a tone value of a minimum tone which is determined depending on a tone value of the one pixel;
2) means for calculating an error as a difference between the tone value of the one pixel and the tone value indicated by the code allocated to the one pixel and setting the error as a negative error when the first code is allocated to the one pixel and as a positive error when the second code is allocated to the one pixel;
3) means for diffusing the calculated error to each of a plurality of the following adjacent pixels, which are located in predetermined positional relationships with the one pixel and are to be processed after the one pixel has been processed, thereby correcting the tone value of each of the following adjacent pixels, such that when the calculated error is the positive error, the tone value of each of the following adjacent pixels is corrected by adding thereto a predetermined proportion of the positive error, and when the calculated error is the negative error, an absolute value of the predetermined proportion of the negative error is compared with an absolute value of the tone value of each of the following adjacent pixels and when the former is larger than the latter, the tone value of each of the following adjacent pixels is replaced by the predetermined proportion of the negative error and when the former is no larger than the latter, the tone value of each of the following adjacent pixels is maintained;
and
4) means for correcting the tone value of the one pixel prior to processing the one pixel by the processing means, when there exists at least one preceding adjacent pixel which is processed before the one pixel is processed and whose error is to be diffused to the one pixel, by the error diffused from the one preceding adjacent pixel by the diffusing means.

2 more elements

Dependencies are inferred from the claim text.