Compression/decompression algorithm for image documents having text, graphical and color content

A computer system including a computer software product for compressing data files representative of an image document, said document including color information and/or graphical information, said computer system including:

• a processor to execute said software instructions;
• a memory storing said software program;
• a display which displays representations of said document;
• said software product disposed on a computer readable medium comprising instructions for causing a computer to:
• provide a first image file of said document at a first resolution and a second image file of said document at a second resolution with said second resolution being lower than said first resolution;
• process the first image file to convert the first image file into a text file representation of the document;
• compress said text file representation of the document to provide a first compressed file;
• process said second file to extract information from the image representation of the document corresponding to color information and graphics information;
• compress the second file using a second compression technique to provide a second compressed file containing information corresponding to the image;
• store said first and second compressed files and said color information to provide a composite compressed file of the document;
• scan the document at a first resolution to provide said first image file at said first resolution and scan the document at a second resolution to provide said second image file at said second resolution;
• determine foreground color corresponding to colors associated with text positions of the document;
• and
• determine the foreground colors by causing the computer to retrieve a plurality of samples of groups of pixels from the low resolution image representation of a document and from each one of said samples of pixels find a pixel corresponding to the minimum and maximum intensity of the pixels in the sample;
• and for each one of said samples
• calculate a threshold value representative of the document by averaging the minimum and maximum intensities for each of the blocks;
• determine a color associated with each one of the blocks and the width of intensity of each one of the blocks;
• and
• provide a color data structure having an entry for each one of said blocks corresponding to a foreground color.

A computer program product for decompressing a file containing image information and text information, said program residing on a computer readable medium comprising instructions for causing a computer to:

• decompress the file containing image information and text information into an image file and a text file;
• allocate a target bit map to represent the decompressed file;
• insert the decompressed image information into the target bit map at locations specified by information contained in said file containing image information and text information;
• insert text information into said target bit map in accordance with positional information provided from the decompressed text file;
• and
• fill the target output bit map with a color corresponding to a dominant background color provided from color information in the file.

A method of compressing an image representation of a document having color portions and text portions comprises the steps of:

• scanning a document to provide a first file at a first resolution and a second file at a second, lower resolution;
• converting the first file into a text file;
• applying an auto-rotate filter to the first file to correct said file for errors;
• converting said high resolution image file into an optical character recognition file having text information and positional information corresponding to the text information on the image document;
• masking portions of said optical character recognition file corresponding to portions of said document representing graphical information associated with the document;
• and
• compressing the unmasked portions of said optical character recognition file to provide a compressed text file;
• applying a rotate filter to the second file to correct errors in said second file;
• determining from said second file foreground colors associated with each of the sections of said document and background colors associated with each portion of said document;
• determining from said background colors a dominant background color that best represents the background color of the document;
• masking portions of said document not corresponding to the graphical portions of the document;
• and
• compressing said unmasked portions to provide a second file corresponding to graphical portions of the document and storing said color information, and said first and second files as a composite file.

A computer system including a computer software product for compressing data files representative of an image document, said document including color information and/or graphical information, said computer system including:

• a processor to execute said software instructions;
• a memory storing said software program;
• a display which displays representations of said document;
• said software product disposed on a computer readable medium comprising instructions for causing a computer to:
• provide a first image file of said document at a first resolution and a second image file of said document at a second resolution with said second resolution being lower than said first resolution;
• process the first image file to convert the first image file into a text file representation of the document;
• compress said text file representation of the document to provide a first compressed file;
• process said second file to extract information from the image representation of the document corresponding to color information and graphics information;
• compress the second file using a second compression technique to provide a second compressed file containing information corresponding to the image;
• store said first and second compressed files and said color information to provide a composite compressed file of the document;
• and
• determine a dominant background color in the file.

A computer system including computer software product for compressing data files representative of an image document, said document including color information and/or graphical information, said computer system including:

• a processor to execute said software instructions;
• a memory storing said software program;
• a display which displays representations of said document;
• said software product disposed on a computer readable medium comprising instructions for causing a computer to:
• provide a first image file of said document at a first resolution and a second image file of said document at a second resolution with said second resolution being lower than said first resolution;
• process the first image file to convert the first image file into a text file representation of the document;
• compress said text file representation of the document to provide a first compressed file;
• process said second file to extract information from the image representation of the document corresponding to color information and graphics information;
• compress the second file using a second compression technique to provide a second compressed file containing information corresponding to the image;
• store said first and second compressed files and said color information to provide a composite compressed file of the document;
• and
• retrieve background color information associating a background color with each one of a plurality of samples of pixels representing the document;
• filter said background colors to provide a target number of colors to represent the background colors;
• apply a median cut analysis to the background color samples to filter said background samples into one of a plurality of boxes corresponding to said target number of colors;
• sort said boxes by increasing volume;
• sort a first portion of said boxes having the smallest amount of volume by decreasing intensity;
• and
• determine the dominant background color as a color to represent the background of the document by the box having the lowest intensity.