Image Compression and Expansion Technique

Abstract

The present invention aims at improving an image compression rate and enhancing quality of images after expansion. An image compression device generates compressed data formed by compressing an image. The device includes a boundary area detection section for detecting boundary areas which include both of internal and external parts of an object rendered in the image, from among plural areas included in the image; a non-boundary area data generation section for, by compressing non-boundary areas which are not the boundary areas in the image, in a predetermined compression mode, generating partial compressed data in the compressed data, corresponding to the non-boundary areas; and a boundary area data generation section for generating partial compressed data in the compressed data, corresponding to the boundary areas, from the boundary areas, in a mode in which difference between images before compression and after expansion is less in comparison with a case where the boundary areas are compressed in the predetermined compression mode.

1 - 16 . (canceled) 
   
   
       17 . An image compression method for generating compressed data formed by compressing an image, the image compression method comprising:
 a boundary area detection step of detecting boundary areas which include both of internal and external parts of an object rendered in the image, from among plural areas included in the image;   a non-boundary area data generation step of, by compressing non-boundary areas which are not the boundary areas in the image, in a predetermined compression mode, generating partial compressed data in the compressed data, corresponding to the non-boundary areas; and   a boundary area data generation step of generating partial compressed data in the compressed data, corresponding to the boundary areas, from the boundary areas, in a mode in which difference between images before compression and after expansion is less in comparison with a case where the boundary areas are compressed in the predetermined compression mode, wherein the image is a telop image to be displayed in a manner that the telop image is superimposed on a background image, and the object is a telop portion of the telop image, wherein the image compression method further comprises a transmittance acquisition step for acquiring a transmittance at which the background image is displayed through the telop image, the transmittance being specified for each pixel, and wherein said boundary area detection step detects each of plural areas included in the telop image as the boundary area if the area includes both of pixels with a transmittance greater than a predetermined first reference transmittance and pixels with a transmittance equal to or smaller than the first reference transmittance.   
   
   
       18 - 19 . (canceled) 
   
   
       20 . Computer readable code stored on computer readable media for causing a computer to function as an image compression device for generating compressed data formed by compressing an image, said computer readable code comprising:
 a boundary area detection subprocess for detecting boundary areas which include both internal and external parts of an object rendered in the image, from among plural areas included in the image;   a non-boundary area data generation subprocess for, by compressing non-boundary areas which are not the boundary areas in the image, in a predetermined compression mode, generating partial compressed data in the compressed data, corresponding to the non-boundary areas; and   a boundary area data generation subprocess for generating partial compressed data in the compressed data, corresponding to the boundary areas, from the boundary areas, in a mode in which difference between images before compression and after expansion is less in comparison with a case where the boundary areas are compressed in the predetermined compression mode, wherein the image is a telop image to be displayed in a manner that the telop image is superimposed on a background image, and the object is a telop portion of the telop image, wherein the computer readable code further comprises a transmittance acquisition subprocess for acquiring a transmittance at which the background image is displayed through the telop image, the transmittance being specified for each pixel, and wherein said boundary area detection subprocess detects each of plural areas included in the telop image as the boundary area if the area includes both of pixels with a transmittance greater than a predetermined first reference transmittance and pixels with a transmittance equal to or smaller than the first reference transmittance.   
   
   
       21 - 22 . (canceled) 
   
   
       23 . The method according to  claim 17 , wherein the transmittance acquisition step acquires a key image in which transmittances of the respective pixels of a telop image, for which transmittances are to be specified, are arranged as brightness values in the same manner as that the pixels of the telop image are arranged, and
 wherein said boundary area data generation section further compresses areas in the key image, corresponding to the boundary areas in the telop image, in the same compression mode in which the boundary areas in the telop image are compressed.   
   
   
       24 . The method according to  claim 17 , further comprising:
 an area-not-to-be-rendered determination step which determines, for each of the plural areas included in the telop image, that the area is an area which is not required to be rendered if the transmittances of all pixels included in the area are greater than a second reference transmittance at which the background image transmits more than at the first reference transmittance; and   an area-not-to-be rendered processing step for compressing the image by removing image data indicating the area determined as an area which is not required to be rendered, from the compressed data, and adding information indicating that the rendering of the area is not required to the compressed data.   
   
   
       25 . The computer readable code, according to  claim 20 , wherein the transmittance acquisition subprocess acquires a key image in which transmittances of the respective pixels of a telop image, for which transmittances are to be specified, are arranged as brightness values in the same manner as that the pixels of the telop image are arranged, and
 wherein said boundary area data generation subprocess further compresses areas in the key image, corresponding to the boundary areas in the telop image, in the same compression mode in which the boundary areas in the telop image are compressed.   
   
   
       26 . The computer readable code, according to  claim 20 , further comprising:
 an area-not-to-be-rendered determination subprocess which determines, for each of the plural areas included in the telop image, that the area is an area which is not required to be rendered if the transmittances of all pixels included in the area are greater than a second reference transmittance at which the background image transmits more than at the first reference transmittance; and   an area-not-to-be rendered processing subprocess for compressing the image by removing image data indicating the area determined as an area which is not required to be rendered, from the compressed data, and adding information indicating that the rendering of the area is not required to the compressed data.