Image compression method and image processing system

• US 5,898,794 A
• Filed: 06/18/1997
• Issued: 04/27/1999
• Est. Priority Date: 11/02/1992
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Morita, Motoyuki, Matsumoto, Hitoshi, Furuta, Shigeki, Sonohara, Satoshi
• Primary Examiner(s): CHANG, JON CARLTON
• Application Number:
  US08/878,201
• Time in Patent Office: 678 Days
• Field of Search: 382/239, 382/253, 382/166, 382/236, 348/411, 348/412, 348/413, 348/404, 348/418, 348/422, 348/390, 348/420, 358/426, 358/524, 358/430, 341/51
• US Class Current: 382/166
• 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

Abstract

Disclosed is an image processing system including an image input unit, an extraction unit, a plurality of compression process parts and a selection unit to compress a 1-frame image down to a less amount of color information. The image input unit takes in a plurality of frame images per frame. The extraction unit extracts each of the taken-in frame images per unit area of a designated size. The plurality of compression process parts effects compression processes different from each other with respect to pels contained in each unit area. The selection unit selects one compression process part from the plurality of compression process parts for compressing the unit area of the designated size.

Claims

1. An image compression method of compressing a 1-frame image consisting of a plurality of pels each having color data of red, green and blue down to less color data quantity, said method comprising:

inputting said 1-frame image included in a plurality of frame images;

setting a designated size for subdividing said 1-frame image;

extracting from said 1-frame image unit areas of said designated size;

effecting compression processes which differ from each other with respect to pels contained in each unit area;

selecting one compression process from said compression processes for compressing said unit areas of said designated size, having a compression rate of said color data quantity higher than other of said compression processes; and

instructing said setting of said designated size to designate a smaller size to lower said compression rate if said compression processes can not be performed at all for said unit areas of said designated size,

wherein said compression processes include

monochrome processing by converting all colors of said pels contained in each unit area within said 1-frame image into a unit area representative color,

in-frame reference processing by converting an original color of each pel contained in non-reference unit areas within said 1-frame image into an in-frame reference color of a corresponding pel contained in an in-frame unit area within said 1-frame image, and

inter-frame reference processing by converting the original color of each pel contained in each unit area within said 1-frame image into an inter-frame reference color of a corresponding pel contained in an inter-frame unit area within another of said frame images.

2. The image compression method as set forth in claim 1, wherein said selection step is to perform said selecting process for said each unit area extracted in said extraction step.

3. The image compression method as set forth in claim 1, further comprising:

a first comparing step of comparing colors of corresponding pels with each other in each unit area and one of said in-frame and inter-frame unit areas; and

a second comparing step of comparing said unit area representative color with a predetermined color reference value.

4. The image compression method as set forth in claim 3, wherein at least one of said in-frame and inter-frame reference processing steps are used if a color difference between said corresponding pels in each unit area and the one of said in-frame unit and inter-frame unit areas falls within a predetermined value in said first comparing step.

5. The image compression method as set forth in claim 3, wherein said monochrome processing step is used if said unit area representative color matches said predetermined color reference value.

6. The image compression method as set forth in claim 1,

wherein said plurality of compression processes further include

a multi-color unit area processing equally subdividing each unit area containing said plurality of pels into equally subdivided unit areas and converting said equally subdivided unit areas to assume different colors, and

a monochrome decode processing unequally subdividing each unit area containing said plurality of pels into unequally subdivided unit areas and converting said unequally subdivided unit areas to assume one color, and

wherein said selecting preferentially selects the one compression process exhibiting the image compression rate higher than other of said compression processes from said compression processes including said multi-color unit area processing and said monochrome decode processing.

7. The image compression method as set forth in claim 1, wherein said plurality of compression processing steps further include a first subsampling step of deleting said pels at a fixed interval among said pels of said unit area and a second subsampling step of extracting a subdivided unit area with no sharp color variation of said pel from said unit area and deleting some of said pels of said subdivided unit area, and said selection step is to preferentially select said step exhibiting a higher image compression rate from said steps including said first and second subsampling steps with respect to said unit area.

8. An image processing system for compressing a 1-frame image consisting of a plurality of pels each having color data of red, green and blue down to less color data quantity, comprising:

an image input unit for inputting frame images, including said 1-frame image;

an extraction unit for setting a designated size for subdividing said 1-frame image and for extracting from said 1-frame image unit areas of said designated size;

a compression processing unit for effecting compression processes which differ from each other with respect to pels contained in each unit area;

a selection unit for selecting one compression process from said compression processes for compressing said unit areas of said designated size, having a compression rate of said color data quantity higher than other of said compression processes; and

an area change instruction unit for instructing said extraction unit to change said designated size to a smaller size to lower said compression rate if said compression processes can not be performed at all for said unit areas of said designated size, and

wherein said compression processes include

monochrome processing by converting all colors of said pels contained in each unit area within said 1-frame image into a unit area representative color,

in-frame reference processing by converting an original color of each pel contained in non-reference unit areas within said 1-frame image into an in-frame reference color of a corresponding pel contained in an in-frame unit area within said 1-frame image, and

inter-frame reference processing by converting the original color of each pel contained in each unit area within said 1-frame image into an inter-frame reference color of a corresponding pel contained in an inter-frame unit area within another of said frame images.

9. The image processing system as set forth in claim 8, wherein said selection unit selects each unit area extracted by said extraction unit.

10. The image processing system as set forth in claim 8, further comprising:

a first comparing unit for comparing colors of corresponding pels with each other in each unit area and said in-frame and inter-frame unit areas; and

a second comparing unit for comparing said unit area representative color with a predetermined color reference value.

11. The image processing system as set forth in claim 10, wherein at least one of said in-frame and inter-frame reference processing are used if a color difference between said corresponding pels in each unit area and said in-frame and inter-frame unit areas, respectively, falls within a predetermined value.

12. The image processing system as set forth in claim 10, wherein said monochrome processing is used if said unit area representative color matches said predetermined color reference value.

13. The image processing system as set forth in claim 8,

wherein said plurality of compression processes further include

multi-color unit area processing equally subdividing each unit area containing said plurality of pels into equally subdivided unit areas and for converting said equally subdivided unit areas to assume different colors, and

monochrome decode processing unequally subdividing each unit area containing said plurality of pels into unequally subdivided unit areas and for converting said unequally subdivided unit areas to assume one color, and

wherein said selecting unit preferentially selects the one compression process exhibiting the image compression rate higher than other of said compression processes from said compression processes including said multi-color unit area processing and said monochrome decode processing.

14. The image processing system as set forth in claim 8,

wherein said plurality of compression processes further include a first subsampling process for deleting said pels at a fixed interval among said pels of each unit area and a second subsampling process for extracting a subdivided unit area with no sharp color variation of said pels in each unit area and for deleting some of said pels of said subdivided unit area, and

wherein said selection unit preferentially selects said one compression process exhibiting a higher image compression rate from said compression processes, including said first and second subsampling processes, with respect to each unit area.

15. An image compression method of compressing a 1-frame image consisting of a plurality of pels each having color data of red, green and blue down to less color data quantity, said method comprising:

inputting said 1-frame image included in a plurality of frame images;

extracting from said 1-frame image unit areas of a designated size;

effecting compression processes which differ from each other with respect to pels contained in each unit area; and

selecting one compression process of said compression processes for compressing said unit areas of said designated size, wherein said processes include monochrome processing by converting all colors of said pels contained in each unit area within said 1-frame image into a unit area representative color, in-frame reference processing by converting an original color of each pel contained in non-reference unit areas within said 1-frame image into an in-frame reference color of a corresponding pel contained in an in-frame unit area within said 1-frame image, and inter-frame reference processing by converting the original color of each pel contained in each unit area within said 1-frame image into an inter-frame reference color of a corresponding pel contained in an inter-frame unit area within another of said frame images.

16. A method of compressing image data representing frames of pels by reducing colors used by the pels, comprising:

selecting a unit area size for processing unit areas in each frame;

selecting a compression process having highest compression from among

a monochrome process of converting a color of each pel contained in each unit area within a current frame into a unit area representative color when the color of each pel in the unit area differs from the unit area representative color by no more than a first reference value,

an in-frame reference process of converting a non-reference color of each pel contained in non-reference unit areas within the current frame into an in-frame reference color of a corresponding pel contained in an in-frame reference unit area within the current frame when the non-reference color and the in-frame reference color differ by no more than a second reference value, and

an inter-frame reference process of converting the non-reference color of each pel contained in each unit area within all non-reference frames into an inter-frame reference color of a corresponding pel contained in an inter-frame reference unit area within a reference frame when the non-reference color and the inter-frame reference color differ by no more than a third reference value;

repeating said selecting of the unit area size and the compression process using a smaller unit area when none of the monochrome, in-frame reference and inter-frame reference processes can be performed; and

processing each unit area of the current frame using the unit area size selected and the compression process selected.

17. A storage medium storing a computer program for a computer to compress a 1-frame image consisting of a plurality of pels each having color data of red, green and blue down to less color data quantity, comprising:

an input segment to input the 1-frame image included in a plurality of frame images;

a size setting segment to set a designated size for subdividing the 1-frame image;

an extraction segment to extract from the 1-frame image unit areas of the designated size;

at least one compression segment to perform compression processes which differ from each other with respect to pels contained in each unit area, the compression processes including

monochrome processing to convert all colors of the pels contained in each unit area within the 1-frame image into a unit area representative color,

in-frame reference processing to convert an original color of each pel contained in non-reference unit areas within the 1-frame image into an in-frame reference color of a corresponding pel contained in an in-frame unit area within the 1-frame image, and

inter-frame reference processing to convert the original color of each pel contained in each unit area within the 1-frame image into an inter-frame reference color of a corresponding pel contained in an inter-frame unit area within another of the frame images;

a selection segment to select one compression process from the compression processes to compress the unit areas of the designated size, having a compression rate of the color data quantity higher than other of the compression processes; and

a size reduction segment to designate a smaller size to lower the compression rate if the compression processes cannot be performed at all for the unit areas of the designated size.

18. A storage medium storing a computer program for a computer to compress a 1-frame image consisting of a plurality of pels each having color data of red, green and blue down to less color data quantity, comprising:

an input segment to input the 1-frame image included in a plurality of frame images;

an extraction segment to extract from the 1-frame image unit areas of a designated size;

at least one compression segment to perform compression processes which differ from each other with respect to pels contained in each unit area, the compression processes including

monochrome processing to convert all colors of the pels contained in each unit area within the 1-frame image into a unit area representative color,

in-frame reference processing to convert an original color of each pel contained in non-reference unit areas within the 1-frame image into an in-frame reference color of a corresponding pel contained in an in-frame unit area within the 1-frame image, and

inter-frame reference processing to convert the original color of each pel contained in each unit area within the 1-frame image into an inter-frame reference color of a corresponding pel contained in an inter-frame unit area within another of the frame images; and

a selection segment to select one compression process of the compression processes to compress the unit areas of the designated size.

19. A storage medium storing a computer program for a computer to compress image data representing frames of pels by reducing colors used by the pels, comprising:

a size selection segment to select a unit area size for processing unit areas in each frame;

a process selection segment to select a compression process having highest compression from among

a monochrome process of converting a color of each pel contained in each unit area within a current frame into a unit area representative color when the color of each pel in the unit area differs from the unit area representative color by no more than a first reference value,

an in-frame reference process of converting a non-reference color of each pel contained in non-reference unit areas within the current frame into an in-frame reference color of a corresponding pel contained in an in-frame reference unit area within the current frame when the non-reference color and the in-frame reference color differ by no more than a second reference value, and

an inter-frame reference process of converting the non-reference color of each pel contained in each unit area within all non-reference frames into an inter-frame reference color of a corresponding pel contained in an inter-frame reference unit area within a reference frame when the non-reference color and the inter-frame reference color differ by no more than a third reference value;

a resizing segment to repeat execution of said size and process selection segments using a smaller unit area when none of the monochrome, in-frame reference and inter-frame reference processes can be performed; and

a process segment to process each unit area of the current frame using the unit area size selected and the compression process selected.