Image processing apparatus

• US 5,898,507 A
• Filed: 07/12/1994
• Issued: 04/27/1999
• Est. Priority Date: 07/16/1993
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Nakane, Rintaro, Kanno, Hiroki
• Primary Examiner(s): Lee, Thomas D.
• Application Number:
  US08/274,305
• Time in Patent Office: 1,750 Days
• Field of Search: 358/448, 358/455, 358/456, 358/458, 358/463, 358/465, 358/466, 382/251, 382/252
• US Class Current: 358/448
• CPC Class Codes: H04N 1/40006 Compensating for the effects of ageing, i.e. changes over time
• CPC Class Codes: H04N 1/4078 using gradational references, e.g. grey-scale test pattern analysis

Abstract

In an image processing apparatus of this invention, an error diffusion processing means having a multi level signal conversion means changes the conversion characteristics of the multi level signal conversion means, e.g., corrects the output value of error diffusion processing, on the basis of an output from a means for detecting a variation in toner attachment amount or image forming condition. That is, this invention executes error diffusion processing as follows when an input dimension is different from an output dimension (e.g., input dimension=reflection factor or density, output dimension=number of gradation levels) with respect to a multi-value conversion means because error diffusion processing cannot be simply performed. The input dimension is set to coincide with the output dimension (an output signal is set to coincide with the input signal), this output signal is changed in accordance with a variation in image density, and an error between the changed output signal and the input signal is calculated, thereby executing error diffusion processing. Even when the gradation characteristics per pixel vary due to the influence of a change in environment or aging, or the number of gradation levels decreases due to the variation, the gradation characteristics in a local area can be maintained good, and initial image quality can be provided over a long period of time.

Claims

1. An image processing apparatus comprising:

scanner means for optically reading an image so as to provide a pixel signal, the pixel signal representing a level of reflectance of light read by said scanner means;

first conversion means for converting the pixel signal provided from said scanner means into a multi level signal;

means for forming an image on an image carrier on the basis of the multi level signal converted by said first conversion means, and further forming a test pattern on the image carrier;

second conversion means for converting said converted multi level signal to a reflectance signal representing the level of light reflected by the image formed by the forming means;

first detecting means for detecting an error between the reflectance signal output from the second conversion means and the pixel signal provided by said scanner means and for calculating a correction value on the basis of the detected error, said correction value being used for correcting a following pixel signal output from the scanner means;

means for correcting the following pixel signal provided from said scanner means on the basis of the correction value calculated by said calculating means;

second detecting means for detecting an image density of the test pattern formed on the image carrier by the forming means; and

means for changing values to be converted by the second conversion means on the basis of the image density of the test pattern detected by the second detecting means, so as to prevent the image on the image carrier from varying in density in spite of an elapse of time and/or changes in environmental conditions.

2. An apparatus according to claim 1, wherein

said forming means comprises exposure means for exposing said image carrier on the basis of the multi level signal so as to form a latent image and means for developing the latent image formed on said image carrier with a developing agent including toner;

and

said detecting means comprises sensor means for detecting an amount of toner attached to said image carrier by said developing means.

3. An apparatus according to claim 1, wherein said changing means comprises a table for storing a plurality of signal levels for changing the reflectance signal, and reading means for reading out an optimal signal level from said table on the basis of the image density detected by said second detecting means.

4. An apparatus according to claim 1, further comprising first memory means for storing weighing coefficients for pixels in the neighborhood of a pixel represented by said pixel signal provided to said conversion means, filter means for obtaining a weighing error in accordance with the weighing coefficient stored in said first memory means and the error calculated by said first detecting means, and second memory means for storing the weighing error obtained by said filter means so as to correct the pixel signal using the weighing error by said changing means.

5. An image processing apparatus comprising:

means for reading an image so as to provide a pixel signal corresponding to the image;

first conversion means for converting the pixel signal provided by said reading means into a first signal representing a density level of the pixel signal;

second conversion means for converting the first signal converted by said first conversion means into a multi level signal;

means for forming an image on an image carrier on the basis of the multi level signal converted by said second conversion means, and further forming a test pattern on the image carrier;

third conversion means for converting said multi level signal from the second conversion means into a second signal representing a density level corresponding to the image formed by the forming means;

first detecting means for detecting an error between the second signal output from the third conversion means and the pixel signal provided by said reading means and for calculating a correction value on the basis of the detected error, said correction value being used for correcting a following pixel signal output from the reading means;

means for correcting the pixel signal provided from said reading means on the basis of the correction value calculated by said calculating means;

second detecting means for detecting an image density of the test pattern formed on the image carrier by the forming means; and

means for changing values to be converted by the third conversion means on the basis of the image density of the test pattern detected by the second detecting means, so as to prevent the image on the image carrier from varying in density in spite of an elapse of time and/or changes in environmental conditions.

6. An apparatus according to claim 5, wherein

said forming means comprises exposure means for exposing said image carrier on the basis of the multi level signal so as to form a latent image and means for developing the latent image formed on said image carrier with a developing agent including toner, and

said second detecting means comprises sensor means for detecting an amount of toner attached to said image carrier by said developing means.

7. An apparatus according to claim 5, wherein said changing means comprises a table for storing a plurality of signal levels for changing the second signal, and reading means for reading out an optimal signal level from said table on the basis of the image density detected by said second detecting means.

8. An apparatus according to claim 5, further comprising first memory means for storing weighing coefficients for pixels in the neighborhood of a pixel represented by said pixel signal provided to said conversion means, filter means for obtaining a weighing error in accordance with the weighing coefficient stored in said first memory means and the error calculated by said first detecting means, and second memory means for storing the weighing error obtained by said filter means so as to correct the pixel signal using the weighing error by said correcting means.

9. An image processing apparatus comprising:

scanner means for optically reading an image so as to provide a pixel signal, the pixel signal representing a level of reflectance of light read by said scanner means;

first conversion means for converting the pixel signal provided from said scanner means into a multi level signal using predetermined threshold levels;

means for forming an image on an image carrier on the basis of the multi level signal converted by said first conversion means, and further forming a test pattern on the image carrier;

second conversion means for converting said converted multi level signal to a reflectance signal representing the level of light reflected by the image formed by the forming means;

first detecting means for detecting an error between the reflectance signal output from the second conversion means and the pixel signal provided by said scanner means and for calculating a correction value on the basis of the detected error, said correction value being used for correcting a following pixel signal output from the scanner means;

means for correcting the following pixel signal provided from said scanner means on the basis of the correction value calculated by said calculating means;

second detecting means for detecting an image density of the test Pattern formed on the image carrier by the forming means; and

means for changing values to be converted by the second conversion means on the basis of the image density of the test pattern detected by the second detecting means, so as to prevent the image on the image carrier from varying in density in spite of an elapse of time and/or changes in environmental conditions, and for changing the threshold levels used by the first conversion means.

10. An apparatus according to claim 9, wherein

said forming means comprises exposure means for exposing said image carrier on the basis of the multi level signal so as to form a latent image and means for developing the latent image formed on said image carrier with a developing agent including toner;

and

said detecting means comprises sensor means for detecting an amount of toner attached to said image carrier by said developing means.

11. An apparatus according to..claim-9, wherein said changing means comprises a table for storing a plurality of signal levels for changing the reflectance signal, and reading means for reading out an optimal signal level from said table on the basis of the image density detected by said detecting means.

12. An apparatus according to claim 9, further comprising first memory means for storing weighting coefficients for pixels in the neighborhood of a pixel represented by said pixel signal provided to said conversion means, filter means for obtaining a weighting error in accordance with the weighting coefficient stored in said first memory means and the error calculated by said calculation means, and second memory means for storing the weighting error obtained by said filter means so as to correct the pixel signal using the weighting error by said correcting means.

13. An image processing apparatus comprising:

means for reading an image so as to provide a pixel signal corresponding to the image;

first conversion means for converting the pixel signal provided by said reading means into a first signal representing a density level of the pixel signal;

second conversion means for converting the first signal converted by said first conversion means into a multi level signal using predetermined threshold levels;

means for forming an image on an image carrier on the basis of the multi level signal converted by said second conversion means, and further forming a test pattern on the image carrier;

third conversion means for converting said multi level signal from the second conversion means into a second signal representing a density level corresponding to the image formed by the forming means;

first detecting means for detecting an error between the second signal output from the third conversion means and the pixel signal provided by said reading means and for calculating a correction value on the basis of the detected error, said correction value being used for correcting a following pixel signal output from the reading means;

means for correcting the pixel signal provided from said reading means on the basis of the correction value calculated by said calculating means;

second detecting means for detecting an image density of the test pattern formed on the image carrier by the forming means; and

means for changing values to be converted by the third conversion means on the basis of the image density of the test pattern detected by the second detecting means, so as to Prevent the image on the image carrier from varying in density in spite of an elapse of time and chances in environmental conditions, and for changing the threshold levels used by the second conversion means.

14. An apparatus according to claim 13, wherein

said forming means comprises exposure means for exposing said image carrier on the basis of the multi level signal so as to form a latent image and means for developing the latent image formed on said image carrier with a developing agent including toner;

and

said detecting means comprises sensor means for detecting an amount of toner attached to said image carrier by said developing means.

15. An apparatus according to claim 13, wherein said changing means comprises a table for storing a plurality of signed levels for changing the second signal, and reading means for reading out an optimal signal level from said table on the basis of the image density detected by said detecting means.

16. An apparatus according to claim 13, further comprising first memory means for storing weighting coefficients for pixels, filter means for obtaining a weighting error the weighting coefficient stored in said first memory means and the error calculated by said calculation means, and second memory means for storing the weighting error to cause said correction means to correct the pixel signal using the weighting error obtained by said filter means.

17. An image processing apparatus comprising:

scanner means for optically reading an image and supplying a pixel signal, the pixel signal representing a level of reflectance of light constituted by a predetermined number of input levels;

first conversion means for converting the pixel signal provided from said scanner means into a multi level signal made up of a predetermined number of output levels equal to the predetermined number of input levels;

means for forming an image on an image carrier on the basis of the multi level signal converted by said first conversion means, and further forming a test pattern on the image carrier;

second conversion means for converting said converted multi level signal to a reflectance signal representing the level of light reflected by the image formed by the forming means;

first detecting means for detecting an error between the reflectance signal output from the second conversion means and the pixel signal provided by said scanner means and for calculating a correction value on the basis of the detected error, said correction value being used for correcting a following pixel signal output from the scanner means;

means for correcting the following pixel signal provided from said scanner means on the basis of the correction value calculated by said calculating means;

second detecting means for detecting an image density of the test pattern formed on the image carrier by the forming means; and

means for changing values to be converted by the second conversion means on the basis of the image density of the test pattern detected by the second detecting means, so as to prevent the image on the image carrier from varying in density in spite of an elapse of time and changes in environmental conditions.

18. An apparatus according to claim 17, wherein

said forming means comprises exposure means for exposing said image carrier on the basis of the multi level signal so as to form a latent image and means for developing the latent image formed on said image carrier with a developing agent including toner;

and

said second detecting means comprises sensor means for detecting an amount of toner attached to said image carrier by said developing means.

19. An apparatus according to claim 17, wherein said changing means comprises a table for storing a plurality of signal levels for changing the reflectance signal, said second detecting means for reading out an optimal signal level from said table on the basis of the image density detected by said detecting means.

20. An apparatus according to claim 17, further comprising first memory means for storing weighting coefficients for pixels, filter means for obtaining a weighting error the weighting coefficient stored in said first memory means and the error calculated by said calculation means, and second memory means for storing the weighting error to cause said correction means to correct the pixel signal using the weighting error obtained by said filter means.

21. An image processing apparatus comprising:

means for supplying a pixel signal representing image density;

means for converting said supplied pixel signal into a multi level signal;

means for forming an image on an image carrier on the basis of the multi level signal converted by said converting means, and further forming a test pattern on the image carrier;

first means for detecting an image density of the image formed on said image carrier by said forming means;

second means for detecting an image density of the test pattern formed on said image carrier by said forming means;

means for changing the multi level signal converted by said converting means in accordance with the image density detected by said second detecting means so as to stabilize the image density changes of the image formed on said image carrier;

means for calculating an error between the level of the multi level signal changed by said changing means and the level of the pixel signal supplied from said supplying means; and

means for correcting a following pixel signal supplied from said supplying means on the basis of the error calculated by said calculating means.

22. An image processing apparatus comprising:

means for supplying a pixel signal representing image density;

means for converting said supplied pixel signal into a multi level signal;

means for forming an image on an image carrier on the basis of the multi level signal converted said converting means;

means for detecting an image forming condition to cause image density changes of the image formed on said image carrier;

means for changing the multi level signal converted said converting means in accordance with the image forming condition detected by said detecting means so as to stabilize the image density changes of the image formed on said image carrier;

means for calculating an error between the level of the multi level signal changed by said changing means and the level of the pixel signal supplied from said supplying means; and

means for correcting a following pixel signal supplied from said supplying means on the basis of the error calculated by said calculating means.

23. An image forming apparatus comprising:

first output means for sequentially outputting first pixel data representing a level of a particular feature of an original image;

first conversion means for converting the first pixel data produced from the first output means into second pixel data;

image forming means, controlled on the basis of the second pixel data produced from the first conversion means, for forming an image;

second conversion means for converting the second pixel data into third pixel data, said third pixel data representing a level of the particular feature of the image formed by the image forming means;

detecting means for detecting an error between the third pixel data output from the second conversion means and the first pixel data, and for calculating a correction value on the basis of the error, said correction value being used for correcting following first pixel data;

correction means for correcting the following first pixel data on the basis of the correction value calculated by the calculating means;

second output means for outputting information regarding variations in the image formed by the image forming means; and

changing means for changing values to be converted by the second conversion means on the basis of the information output from the second output means, such that the variations in the image are compensated for.

24. An image forming apparatus comprising:

first output means for sequentially outputting first pixel data representing a level of a particular feature of an original image;

image forming means, controlled on the basis of the first pixel data produced from the first output means, for forming an image;

conversion means for converting the first pixel data into second pixel data representing a level of the particular feature of the image formed by the image forming means;

detecting means for detecting an error between the second pixel data output from the conversion means and the first pixel data, and for calculating a correction value on the basis of the error, said correction value being used for correcting following first pixel data;

correction means for correcting the following first pixel data on the basis of the correction value calculated by the calculating means;

second output means for outputting information regarding variations in the image formed by the image forming means; and

changing means for changing values to be converted by the conversion means on the basis of the information output from the second output means, such that the variations in the image are compensated for.