Magnifying digital image using edge mapping

• US 5,446,804 A
• Filed: 04/14/1994
• Issued: 08/29/1995
• Est. Priority Date: 04/14/1994
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Wong, Ping W., Allebach, Jan P.
• Primary Examiner(s): Moore, David K.
• Assistant Examiner(s): CAMMARATA, MICHAEL
• Application Number:
  US08/227,764
• Time in Patent Office: 502 Days
• Field of Search: 382/47, 382/22, 382/49, 382/54, 395/128, 395/102, 395/139, 348/63, 348/581, 348/582, 345/130, 358/525, 358/528
• US Class Current: 382/298
• CPC Class Codes: G06T 3/4023 based on decimating pixels or lines of pixels; based on inserting pixels or lines of pixels
• CPC Class Codes: G06T 3/403 Edge-driven scaling; Edge-based scaling
• CPC Class Codes: G06T 7/12 Edge-based segmentation

Abstract

A method of magnifying a digital image based on an edge map. The image has many original pixels, with each pixel having a level, and the locations of the pixels having a resolution. The method to magnify the image includes the steps of producing an edge map with many boundaries from the digital image, projecting the edge map onto the digital image, generating one or more additional pixels in locations among the original pixels by manipulating the levels of one or more original pixels without crossing any boundaries set by the edge map, and expanding the distances between the pixels so that the resolution of the locations of the pixels becomes the same as the original pixels. In another preferred embodiment, the original digital image is enlarged to the size of the magnified image by extending proportionally the locations of the original pixels. Then the edge map is produced and projected onto the enlarged image to generate additional pixels. After the step of generating, the resolution of the locations of the pixels becomes the same as the original pixels.

Claims

1. A method of magnifying a digital image with a plurality of original pixels to form a magnified image, each pixel having a level, the locations of the pixels having a resolution, the method comprising the steps of:

producing an edge map with a plurality of boundaries by analyzing the digital image to pick locations in neighborhoods where levels change significantly and then connecting the picked locations to form edges;

projecting the edge map onto the digital image; and

generating one or more additional pixels in locations among the original pixels by manipulating the levels of one or more original pixels that do not have among them any boundaries set by the edge map;

such that the total number of additional pixels is related to the number of original pixels and the magnification.

2. A method as recited in claim 1 further comprising the step of:

expanding, after the step of generating, the distances between all the pixels to generate the magnified image so that the resolution of the locations of all the pixels in the magnified image becomes the same as the original pixels in the digital image.

12. A method as recited in claim 2 wherein the step of generating further comprises the step of interpolating the levels of one or more original pixels to create the levels of one or more additional pixels in the immediate neighborhood of the original pixels.

13. A method as recited in claim 1 wherein the image is two-dimensional and the edge map includes one or more lines.

14. A method as recited in claim 1 wherein the image is three-dimensional and the edge map includes one or more surfaces.

15. A method as recited in claim 1 wherein the image is in monochrome.

16. A method as recited in claim 1 wherein the image is in color.

18. A method as recited in claim 1 wherein the image is a halftone image, and the method further comprising two additional steps,

inverse halftoning the image to form a continuous image before performing the method as recited in claim 1;

and

halftoning the resultant image to form a halftone image after performing the method as recited in claim 1.

3. A method of magnifying a digital image with a plurality of original pixels to form a magnified image, each pixel having a level, the locations of the pixels having a resolution, the method comprising the steps of:

enlarging the digital image to the size of the magnified image by expanding proportionally the distances separating the original pixels;

producing an edge map with a plurality of boundaries by analyzing the digital image that has been enlarged to pick locations in neighborhoods where levels change significantly and then connecting the picked locations to form edges;

projecting the edge map onto the digital image that has been enlarged; and

generating one or more additional pixels in locations among the original pixels by manipulating the levels of one or more original pixels that do not have among them any boundaries set by the edge map;

such that;

the total number of additional pixels is related to the number of original pixels and the magnification;

after the step of generating, the digital image that has been enlarged becomes the magnified image; and

the resolution of the locations of all the pixels in the magnified image becomes the same as the original pixels in the digital image before it was enlarged.

4. A method of magnifying a digital image with a plurality of original pixels to form a magnified image, each pixel having a level the locations of the pixels having a resolution, the method comprising the steps of:

producing an edge map with a plurality of boundaries by;

analyzing the digital image to pick locations in neighborhoods where levels change significantly; and

connecting any two picked locations to form an edge if the distance between the locations is less than or equal to the minimum distance between two adjacent original pixels;

projecting the edge map onto the digital image;

generating one or more additional pixels in locations among the original pixels by manipulating the levels of one or more original pixels that do not have among them any boundaries set by the edge map; and

expanding the distances between all the pixels to generate the magnified image so that the resolution of the locations of all the pixels in the magnified image becomes the same as the original pixels in the digital image;

such that the total number of additional pixels is related to the number of original pixels and the magnification.

5. A method as recited in claim 4 wherein the step of analyzing further comprises:

representing each pixel by an impulse function with its magnitude being equal to the level of its corresponding pixel;

selecting a singly-peaked continuous function;

differentiating the selected function twice;

convolving in selected locations in the digital image the differentiated function with the impulse functions; and

picking the locations where the convolving step generates substantially a zero.

6. A method as recited in claim 4 wherein the step of analyzing further comprises:

representing each pixel by an impulse function with its magnitude being equal to the level of its corresponding pixel;

selecting a singly-peaked continuous function;

convolving at selected locations in the digital image the selected function with the impulse functions;

differentiating twice the convolved results; and

picking the locations where the differentiating step generates substantially a zero.

7. A method as recited in claim 5 wherein the continuous function is a Gaussian function.

8. A method as recited in claim 5 wherein the step of picking further comprises the step of thresholding, which removes any picked location with its local level variances less than a pre-selected value.

9. A method as recited in claim 6 wherein the step of picking further comprises the step of thresholding, which removes any picked location with its local level variances less than a pre-selected value.

10. A method as recited in claim 5 wherein the step of picking further comprises the steps of:

forming temporary pixels at selected locations in the digital image;

evaluating the levels at the temporary pixels from the results of the convolving step;

comparing the levels of adjacent temporary pixels;

selecting those pairs of adjacent temporary pixels whose levels change sign; and

choosing each location based on the temporary pixel, from every selected pair, whose level is closer to zero.

11. A method as recited in claim 6 wherein the step of picking further comprises the steps of:

forming temporary pixels at selected locations in the digital image;

evaluating the levels at the temporary pixels from the results of the differentiating step;

comparing the levels of adjacent temporary pixels;

selecting those pairs of adjacent temporary pixels whose levels change sign; and

choosing each location based on the temporary pixel, from every selected pair, whose level is closer to zero.

17. A method of magnifying a digital image with a plurality of original pixels to form a magnified image, each pixel having a level, the locations of the pixels having a resolution, the method comprising the steps of:

producing an edge map with a plurality of boundaries from the digital image;

projecting the edge map onto the digital image;

generating one or more additional pixels in locations among the original pixels by manipulating the levels of one or more original pixels that do not have among them any boundaries set by the edge map;

selecting a window size;

for every additional pixel in the immediate neighborhood of the boundaries,

centering the window to that additional pixel,

calculating the average level of the original pixels within the window and on the same side of the boundary as the additional pixel, and

replacing the level of the additional pixel with the average level if the level of the additional pixel differs by more than a certain value from the average; and

expanding, after the step of generating, the distances between all the pixels to generate the magnified image so that the resolution of the locations of all the pixels in the magnified image becomes the same as the original pixels in the digital image;

such that the total number of additional pixels is related to the number of original pixels and the magnification.