Image compression apparatus, method and recording medium storing an image compression program

Abstract

An image compression apparatus and method, and a carrier wave encoded with a computer readable control program having instructions for use by a computer, perform an image compression process. A compression level is determined for use in compressing a picture image to a predetermined target data amount by iteratively compressing a reduced version of the picture image in order to determine the compression level that is to be used to compress the picture image. First, a reduced-size picture image is created from the picture image that is to be compressed. A preliminary compression target data amount is then derived, for example, based on the target data amount, the data amount of the picture image and the data amount of the reduced-size picture image. The reduced-size picture image is then compressed using a compression level. The size of the resulting compressed reduced-size picture image is compared to the preliminary compression target data amount. The compression level is then adjusted (raised or lowered) and compression of the reduced-size picture image is repeated until the resulting compressed reduced-size picture image satisfies the preliminary compression target data amount. The compression level that ultimately is derived, is then used to compress the picture image. The resulting compressed picture image will then satisfy the predetermined target data amount.

What is claimed is:  
     
         1 . A picture image compression apparatus that compresses data of a picture image to a predetermined target data amount, comprising: 
 picture image creation means for creating, from the picture image, a reduced-size picture image having a reduced number of picture elements of the picture image;    preliminary compression means for deriving a compression level that compresses the reduced-size picture image to a preliminary compression target data amount that is related to the predetermined target data amount; and    compression means for compressing the data of the picture image to the target data amount using the compression level derived by the preliminary compression means.    
     
     
         2 . The picture image compression apparatus of  claim 1 , wherein the picture image creation means creates a field picture image as the reduced-size picture image.  
     
     
         3 . The picture image compression apparatus of  claim 1 , wherein the picture image creation means creates a thumbnail picture image as the reduced-size picture image.  
     
     
         4 . The picture image compression apparatus of  claim 3 , wherein a plurality of the thumbnail picture images are capable of being displayed in a single-view display.  
     
     
         5 . The picture image compression apparatus of  claim 1 , wherein the preliminary compression means derives the compression level by repeatedly compressing the reduced-size picture image using different compression levels until a compression level is used that results in the preliminary compression target data amount being obtained.  
     
     
         6 . The picture image compression apparatus of  claim 1 , wherein the preliminary compression means and the compression means perform compression by omitting redundant data from the picture image and the reduced-size picture image.  
     
     
         7 . The picture image compression apparatus of  claim 1 , farther comprising data amount determination means for deriving the preliminary compression target data amount from the predetermined target data amount.  
     
     
         8 . The picture image compression apparatus of  claim 7 , wherein the data amount determination means also derives the preliminary compression target data amount from a ratio between data amounts of the picture image and the reduced-size picture image.  
     
     
         9 . The picture image compression apparatus of  claim 1 , wherein the picture image compression apparatus is an electronic camera having picture image input means for photoelectrically converting an object image into the data of the picture image.  
     
     
         10 . The picture image compression apparatus of  claim 1 , wherein the preliminary compression target data amount is less than the predetermined target data amount.  
     
     
         11 . A picture image compression apparatus that compresses data of a picture image to a predetermined target data amount, comprising: 
 picture image processor that creates, from the picture image, a reduced size picture image having a reduced number of picture elements of the picture image;    a compression circuit; and    a controller that uses the compression circuit to derive a compression level that compresses the reduced-size picture image to a preliminary compression target data amount that is related to the predetermined target data amount, the controller then using the compression circuit to compress the data of the picture image to the target data amount using the derived compression level.    
     
     
         12 . The picture image compression apparatus of  claim 11 , wherein the picture image processor creates a field picture image as the reduced-size picture image.  
     
     
         13 . The picture image compression apparatus of  claim 11 , wherein the picture image processor creates a thumbnail picture image as the reduced-size picture image.  
     
     
         14 . The picture image compression apparatus of  claim 11 , wherein the compression circuit performs compression by omitting redundant data from the picture image that is to be compressed.  
     
     
         15 . The picture image compression apparatus of  claim 14 , wherein the compression circuit is a JPEG compression circuit.  
     
     
         16 . The picture image compression apparatus of  claim 11 , wherein the picture image compression apparatus is an electronic camera having a photoelectric converter that converts an object image into the data of the picture image.  
     
     
         17 . The picture image compression apparatus of  claim 11 , wherein the preliminary compression target data amount is less than the predetermined target data amount.  
     
     
         18 . A method of determining a compression level to be used to compress data of a picture image to a predetermined target data amount, comprising the steps of: 
 creating, from the picture image, a reduced-size picture image having a reduced number of picture elements of the picture image; and    deriving the compression level by compressing the reduced-size picture image to a preliminary compression target data amount that is related to the predetermined target data amount.    
     
     
         19 . The method of  claim 18 , further comprising the step of compressing the data of the picture image to the target data amount using the derived compression level.  
     
     
         20 . The method of  claim 18 , wherein the reduced-size picture image is a field picture image.  
     
     
         21 . The method of  claim 18 , wherein the reduced-size picture image is a thumbnail picture image.  
     
     
         22 . The method of  claim 18 , wherein the step of deriving the compression level includes repeatedly compressing the reduced-size picture image using different compression levels until a compression level is used that results in the preliminary compression target data amount being obtained.  
     
     
         23 . The method of  claim 18 , further comprising deriving the preliminary compression target data amount from the predetermined target data amount.  
     
     
         24 . The method of  claim 23 , wherein the preliminary compression target data amount also is derived from a ratio between data amounts of the picture image and the reduced-size picture image.  
     
     
         25 . The method of  claim 18 , wherein the preliminary compression target data amount is less than the predetermined target data amount.  
     
     
         26 . A computer-readable data signal embodied in a carrier wave, the data signal encoded to transmit a control program for determining a compression level to be used to compress data of a picture image to a predetermined target data amount, the control program including instructions for: 
 creating, from the picture image, a reduced-size picture image having a reduced number of picture elements of the picture image; and    deriving the compression level by compressing the reduced-size picture image to a preliminary compression target data amount that is related to the predetermined target data amount.    
     
     
         27 . The data signal of  claim 26 , wherein the control program further includes instructions for compressing the data of the picture image to the target data amount using the derived compression level.  
     
     
         28 . The data signal of  claim 26 , wherein the creating instruction is to create the reduced-size picture image by creating a field picture image.  
     
     
         29 . The data signal of  claim 26 , wherein the creating instruction is to create the reduced-size picture image by creating a thumbnail picture image.  
     
     
         30 . The data signal of  claim 26 , wherein the instruction to derive the compression level includes an instruction to repeatedly compress the reduced-size picture image using different compression levels until a compression level is used that results in the preliminary compression target data amount being obtained.  
     
     
         31 . The data signal of  claim 26 , further comprising an instruction to derive the preliminary compression target data amount from the predetermined target data amount.  
     
     
         32 . The data signal of  claim 31 , wherein the preliminary compression target data amount also is derived from a ratio between data amounts of the picture image and the reduced-size picture image.  
     
     
         33 . The data signal of  claim 26 , wherein the preliminary compression target data amount is less than the predetermined target data amount.  
     
     
         34 . The data signal of  claim 26 , including a computer-readable recording medium on which the carrier wave is recorded.