Subpixel character positioning with antialiasing with grey masking techniques

• US 5,701,365 A
• Filed: 06/21/1996
• Issued: 12/23/1997
• Est. Priority Date: 06/21/1996
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Klassen, R. Victor, Harrington, Steven J.
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US08/667,692
• Time in Patent Office: 550 Days
• Field of Search: 358/450, 358/454-459, 395/101, 395/109, 395/110, 395/131, 395/133, 395/141-143, 382/212, 382/213-214, 382/298-299
• US Class Current: 382/212
• CPC Class Codes: G06T 2200/12 involving antialiasing
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction

Abstract

A method for combining foreground objects defined by a mask value and shade value, with a background image defined by a shade value, using high resolution edge information derived from low resolution grey image representations. By treating the object edge pixels in a high resolution grey model, characteristics of an edge represented by an edge pixel can be approximated by reference to surrounding grey elements. Movement of the edge can be approximated by changing the mask values in the high resolution grey model. Changes in the overall grey level of the pixel resulting from the mask changes cause the impression of edge movement in the low resolution edge.

Claims

1. A method for making small changes in edge position in continuous tone images combining an existing image A, a grey mask M and a shade value C for an object to be added to image A, including the steps of:

1) providing an gray mask including pixels having contone values employing a number of gray levels G greater than 2;

2) expanding gray mask M to a bitmap m defined in terms of subpixels;

3) translating or moving m with respect to image A some number of subpixels to yield a translated mask m'"'"';

4) finding pixels in A overlapped by m'"'"';

5) expanding those pixels found in A to a bytemap of subpixels B;

6) replacing any subpixels of the expanded pixels corresponding to ink in m'"'"' with said shade value C; and

7) filtering those pixels in B and returning the filtered pixels to A.

2. The method of claim 1 where the plurality of subpixels for each pixel is a predetermined number N.

3. The method of claim 1 where step 2 includes:

a) determining from the mask value for the pixel of interest a number p of subpixels that should be permeable;

b) determining a fractional permeability value for each subpixel as a function of the mask value of the pixel of interest, the mask value of at least one neighboring pixel in the plurality thereof and the relative position of the subpixel in the pixel of interest to the at least one neighbor;

c) sorting the determined fractional permeability values by magnitudes, and identifying those subpixels having the p largest magnitudes as permeable.

4. The method of claim 1 where the expanding in step 5 includes:

a) determining for the pixel of interest and the plurality of neighboring pixels a minimum shade value and a maximum shade value;

b) determining a shade value for each subpixel as a function of the shade value of the pixel of interest, the shade value of at least one neighbor and the relative position of the subpixel in the pixel of interest and the at least one neighbor;

c) sorting the determined shade values by magnitude, assigning the maximum shade value to subpixels having the q largest shade values and assigning the minimum shade value to the remaining subpixels.

5. The method as defined in claim 3, wherein the plurality of neighbors includes 8 adjacent pixels.

6. The method as defined in claim 2, wherein the predetermined number of subpixels is about 25.

7. The method as defined in claim 3, wherein p is determined by the function:

space="preserve" listing-type="equation">p=.sup.SM /.sub.N

where M is the mask value of the pixel of interest, S is the number of subpixels and N is the value of a fully permeable pixel.

8. A method for making small changes in object edge position in continuous tone images combining an existing image A, a grey mask M and a color C for an object to be added to image A, including the steps of:

1) providing an gray mask including pixels having contone values employing a number of gray levels G greater than 2;

2) expanding gray mask M to a bitmap m;

3) translating or moving m with respect to image A by some number of subpixels to obtain translated bitmap m'"'"';

4) combining the values of translated bitmap m'"'"' to yield a new antialiased mask M'"'"' at the translated location;

5) finding pixels in image A overlapped by new antiialiased mask M'"'"';

6) alpha blending the current color C with the existing image A using the new antialiased mask M'"'"' as an alpha factor to determine the new image.

9. The method of claim 8 where the plurality of subpixels for each pixel is a predetermined number N.

10. The method of claim 8 where step 2 includes:

a) determining from the mask value for the pixel of interest a number p of subpixels that should be permeable;

b) determining a fractional permeability value for each subpixel as a function of the mask value of the pixel of interest, the mask value of at least one neighboring pixel in the plurality thereof and the relative position of the subpixel in the pixel of interest from the at least one neighbor;

,

c) sorting the determined fractional permeability values by magnitude, and identifying those subpixels having the p largest magnitudes as permeable.

11. The method of claim 8 where the combining of step 4 includes averaging the mask values of all the subpixels in the pixel of interest.

12. The method as defined in claim 10, wherein the plurality of neighbors includes 8 adjacent pixels.

13. The method as defined in claim 9, wherein the predetermined number of subpixels is about 25.

14. The method as defined in claim 10, wherein p is determined by the function:

space="preserve" listing-type="equation">p=.sup.SM /.sub.N

where M is the mask value of the pixel of interest, S is the number of subpixels and N is the value of a fully permeable pixel.

15. A method of translating antialiased edges expressed by an object mask with improved edge rendition, said edges including pixels and the method including:

1) providing an object mask including pixels having contone values employing a number of gray levels G greater than 2;

2) providing a high resolution version of the pixels of interest in the mask, including a plurality of subpixels;

3) assigning a binary mask value to each subpixel as a function of a position thereof within the pixel of interest and the values of any pixels neighboring the pixel of interest;

4) accumulating high resolution versions of pixels in the scope of the desired translation about the pixel of interest;

5) varying the mask values of the subpixels to translate the edge position within the pixel of interest;

6) combining the subpixel mask values in the pixel of interest to determine a final output value for the pixel of interest.

16. The method of claim 15 where step 2 includes receiving a plurality of neighboring pixels for each of the pixels of interest.

17. The method of claim 15 where the plurality of subpixels for each pixel is a predetermined number N.

19. The method of claim 15 where the combining of step 6 includes averaging the mask values of all the subpixels in the pixel of interest.

20. The method as defined in claim 16, wherein the plurality of neighbors includes 8 adjacent pixels.

21. The method as defined in claim 17, wherein the predetermined number of subpixels is about 25.

18. The method of 17 where step 3 includes:

1) determining from the mask value for the pixel of interest a number p of subpixels that should be permeable;

2) determining a fractional permeability value for each subpixel as a function of the mask value of the pixel of interest, the mask value of at least one neighboring pixel in the plurality thereof and the relative position of the subpixel in the pixel of interest from the at least one neighbor;

3) sorting the determined fractional permeability values by magnitudes, and identifying those subpixels having the p largest magnitudes as permeable.

22. The method as defined in claim 18, wherein p is determined by the function:

space="preserve" listing-type="equation">p=.sup.SM /.sub.N

where M is the mask value of the pixel of interest, S is the number of subpixels and N is the value of a fully permeable pixel.