Image processing method, image compression device and mobile terminal

• US 9,082,160 B2
• Filed: 12/04/2012
• Issued: 07/14/2015
• Est. Priority Date: 12/05/2011
• Status: Active Grant

• Current Assignee: Alibaba Group Holding Ltd.
• Original Assignee: Uc Mobile Co., Ltd. (Alibaba Group Holding Ltd.), Guangzhou Ucweb Computer Technology Company, Ltd.
• Inventors: Liang, Jie
• Primary Examiner(s): Krasnic, Bernard
• Application Number:
  US14/128,861
• Publication Number:
  US 20140212033A1
• Time in Patent Office: 952 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00
• CPC Class Codes: H04N 1/642 Adapting to different types of images, e.g. characters, graphs, black and white image portions

Abstract

The present invention provides an image compression method, comprising: determining non-edge portions of an image to be compressed by performing an image edge detection on the image to be compressed; dividing each of non-edge portions into a plurality of connected domains of pixels according to color similarity of the pixels in the non-edge portion, wherein each of the connected domains of pixels is composed of a pixel selected during the division into the connected domains of pixels and the pixels similar in color to and continuously adjacent to the selected pixel; setting the color of each of the connected domains of pixels to be the color of the selected pixel; merging the colors of a plurality of divided connected domains of pixels according to similarity of the colors of the connected domains of pixels; and compressing the image to be compressed by using the merged colors. According to the method, the number of colors used for image compression can be determined according to the characteristics of the image, thus the file size of the compressed image can be effectively reduced with the display effect thereof kept substantially unchanged.

Claims

1. An image compression method, comprising steps of:

determining non-edge portions of an image to be compressed by performing an image edge detection on the image to be compressed;

dividing each of the determined non-edge portions into a plurality of connected domains of pixels according to color similarity of the pixels in the non-edge portion, wherein each of the connected domains of pixels is composed of a pixel selected during the division into the connected domains of pixels and pixels similar in color to and continuously adjacent to the selected pixel;

setting a color of each of the connected domains of pixels to a represented color, wherein the represented color is the color of the pixel selected during the division into the connected domains of pixels;

building a first compression list including a plurality of entries, wherein each entry corresponds to the represented color of each of the connected domains of pixels;

performing a color merging process on the entries in the first compression list to obtain a final image compression color list, wherein the represented colors of the connected domains of pixels which are not adjacent and having similar represented colors are modified to a same color; and

compressing the image to be compressed by using colors in the final image compression color list.

2. The image compression method according to claim 1, wherein the step of dividing each of the determined non-edge portions into a plurality of connected domains of pixels according to color similarity of the pixels in the non-edge portion comprises:

selecting a pixel from the pixels of the non-edge portion;

searching pixels similar in color to and continuously adjacent to the selected pixel, starting from the selected pixel;

forming a connected domain of pixels with the searched pixels and the selected pixel; and

selecting another pixel in the remaining pixels that are not divided into connected domains of pixels yet and repeating the above procedure of forming a connected domain of pixels, till the pixels in the non-edge portion are all divided into connected domains of pixels.

3. The image compression method according to claim 1, wherein Sobel edge detection algorithm is used to perform the image edge detection on the image to be compressed.

4. The image compression method according to claim 1, wherein the step of performing a color merging process on the entries in the first compression list to obtain a final image compression color list comprises:

in the first compression list, selecting a connected domain of pixels from the plurality of connected domains of pixels;

determining connected domains of pixels similar in color to the selected connected domain of pixels from the other connected domains of pixels in the plurality of connected domains of pixels;

in the final image compression color list, modifying the colors of the connected domains of pixels which are not adjacent and are similar in color to the selected connected domain of pixels into the color of the selected connected domain of pixels; and

selecting another connected domain of pixels from the remaining connected domains of pixels that are not subject to a color merging process yet and repeating the above procedure, till all the connected domains of pixels are subject to a color merging process.

5. The image compression method according to claim 1, wherein the having similar represented colors is determined by calculating a difference value between two represented colors.

6. The image compression method according to claim 5, wherein two represented colors are similar if the difference value between the two represented colors is less than a predetermined threshold.

7. An image compression device, comprising:

a non-edge portion determining unit for determining non-edge portions of an image to be compressed by performing an image edge detection on the image to be compressed;

a connected-domain-of-pixels dividing unit for dividing each of the determined non-edge portions into a plurality of connected domains of pixels according to color similarity of the pixels in the non-edge portion, wherein each of the connected domains of pixels is composed of a pixel selected during the division into the connected domains of pixels and pixels similar in color to and continuously adjacent to the selected pixel;

a color setting unit for setting a color of each of the connected domains of pixels to a represented color, wherein the represented color is the color of the pixel selected during the division into the connected domains of pixels;

a color merging unit for building a first compression list including a plurality of entries, wherein each entry corresponds to the represented color of each of the connected domains of pixels; and

performing a color merging process on the entries in the first compression list to obtain a final image compression color list, wherein the represented colors of the connected domains of pixels which are not adjacent and having similar represented colors are modified to a same color; and

a compressing unit for compressing the image to be compressed by using colors in the final image compression color list.

8. The image compression device according to claim 7, wherein the connected-domain-of-pixels dividing unit comprises:

a first selecting module for selecting a pixel from the pixels of the non-edge portion;

a searching module for searching pixels similar in color to and continuously adjacent to the selected pixel, starting from the selected pixel;

a forming module for forming a connected domain of pixels with the searched pixels and the selected pixel;

a first deciding module for deciding whether all the pixels in the non-edge portion are divided,

wherein if the first deciding module decides that there exist remaining pixels that are not divided yet, the first selecting module, the searching module and the forming module repeatedly performs treatments on the remaining pixels.

9. The image compression device according to claim 8, wherein the color merging unit comprises:

a second selecting module for selecting a connected domain of pixels from the plurality of connected domains of pixels in the first compression list;

a determining module for determining connected domains of pixels similar in color to the selected connected domain of pixels from the other connected domains of pixels in the plurality of connected domains of pixels;

a color modifying module for modifying the colors of the connected domains of pixels which are not adjacent and are similar in color to the selected connected domain of pixels into the color of the selected connected domain of pixels in the final image compression color list; and

a second deciding module for deciding whether all the connected domains of pixels are subject to a color merging process,

wherein if the second deciding module decides that there exist remaining connected domains of pixels that are not subject to a color merging process yet, the second selecting module, the determining module and the color modifying module repeatedly performs treatments on the remaining connected domains of pixels.

10. The image compression device according to claim 7, wherein the having similar represented colors is determined by calculating a difference value between two represented colors.

11. The image compression device according to claim 10, wherein two represented colors are similar if the difference value between the two represented colors is less than a predetermined threshold.

12. A mobile terminal, comprising the image compression device according to claim 7.