Transmission and storage of digital images are routine operations for networked computing devices. Digital images represent a substantial fraction of the volume of data necessary to represent a web page. Although network speed and data storage capacity have steadily increased with time, enabling the transmission and storage of ever larger digital images, there are advantages to reducing image data file sizes via compression. For example, web hosting services often charge their client web site owners on the basis of one or more of per file download, per megabyte transferred, and per megabyte of storage. Minimizing file sizes for images stored on a web server or the number and size of files delivered by a web server to a user's web browser can lead to substantial cost savings for hosted web site owners.
Image compression techniques such as those associated with the standard JPEG and PNG image file formats are commonly employed to reduce image storage and transmission requirements. Generally, digital images comprised of few colors or large areas of uniform color compress better than highly-detailed or textured images. Although compression ratios produced by the standard algorithms can be significant, in certain circumstances there is room for further improvement.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a method that effectively and efficiently exploits the similarity between a plurality of digital images during compression.