Conversion of higher resolution images for display on a lower-resolution display device

• US 5,528,740 A
• Filed: 02/25/1993
• Issued: 06/18/1996
• Est. Priority Date: 02/25/1993
• Status: Expired due to Fees

• Current Assignee: Document Technologies LLC
• Original Assignee: Document Technologies LLC
• Inventors: Hill, Timothy J., Marsh, Robert M., Newcomb, Jesse C.
• Primary Examiner(s): Zimmerman, Mark K.
• Assistant Examiner(s): Wingard, Jody R.
• Application Number:
  US08/023,107
• Time in Patent Office: 1,209 Days
• Field of Search: 395/128, 382/225, 382/227, 382/232, 382/233
• US Class Current: 345/428
• CPC Class Codes: G06T 3/4023 based on decimating pixels or lines of pixels; based on inserting pixels or lines of pixels
• CPC Class Codes: G09G 5/391 Resolution modifying circuits, e.g. variable screen formats
• CPC Class Codes: G09G 5/393 Arrangements for updating the contents of the bit-mapped memory
• CPC Class Codes: G09G 5/395 Arrangements specially adapted for transferring the contents of the bit-mapped memory to the screen G09G5/399 takes precedence

Abstract

A system for converting a high-resolution bitonal bit map representation of a document to a lower-resolution pixel representation for display. A special subset of the high resolution output is assigned special meanings by codes which are used to produce a real time video signal with higher bandwidth to enhance the resolution and readability of the displayed image on a lower resolution display. This is accomplished by splitting each coded pixel into two or more "twixels". The twixels produced from pixels which are not part of the special subset have the same codes as the corresponding original pixels. The twixels produced from pixels which are part of the special subset have special codes which, when displayed, duplicate certain predetermined high resolution features of the original bitonal pixel-code information on a display.

Claims

1. An image-processing system for converting a higher-resolution bitonal bit image representation to lower-resolution pixel-code information retaining in decodable form certain predetermined high resolution features of the bitonal bit image representation suitable for display, the system comprising:

means for converting original bitonal pixel-code information from a document scanned with a resolution of n dots per inch to lower resolution pixel-code information, where the resolution of the lower resolution pixel-code information is less than n dots-per-inch, where said original bitonal pixel-code information is divided into a plurality of clusters of pixels, each said cluster corresponding to a pixel in said lower resolution pixel-code information;

a gray scale having m gray levels, each said gray level having a corresponding gray scale value;

a subset of said m gray levels, each gray level in said subset further having a corresponding plurality of special pixel values, whereby said subset of gray levels and said corresponding special pixel values represent certain pixel configurations in said plurality of clusters to provide an approximation to said predetermined high resolution features of said original bitonal pixel-code information;

wherein said means for converting includes means for selecting one of said clusters of pixels from said original bitonal pixel-code information and means for selecting one of said gray scale values based upon a configuration of pixel-codes within said selected cluster;

means for storing said selected gray scale value for the pixel in the lower resolution pixel-code information corresponding to said selected cluster; and

means for decoding the stored lower resolution pixel-code information to produce an output data stream for display;

wherein said means for decoding includes means for recognizing gray scale values which correspond to gray levels belonging to said subset of gray levels and means, responsive to said means for recognizing, for outputting to said output data stream said plurality of special pixel values corresponding to gray levels of said recognized gray scale values, thereby substituting said recognized gray scale values in said output data stream with said plurality of special pixel values and reconstructing the predetermined high resolution features of the bitonal coded pixel-code information using the special pixel values.

2. The system of claim 1 wherein the means for decoding includes means for splitting all said pixels in said lower resolution pixel-code information into two or more twixels in the output data stream.

3. The system of claim 2 wherein each pixel having a gray level that is not within said subset of gray levels is split into symmetric twixels, each having the same gray scale value and wherein each pixel having a gray level that is within said subset of gray levels is split into asymmetric twixels, each having one of said plurality of special pixel values corresponding to said gray level to duplicate the certain predetermined high resolution features of the original bitonal pixel-code information.

4. The system of claim 2 wherein pixels are split into horizontally spaced twixels thereby increasing the horizontal resolution of the displayed images.

5. The system of claim 1:

wherein the means for storing the lower resolution pixel-code information includes a graphic display memory having two-phase output signals;

wherein the means for decoding includes data decoding logic means for receiving the two-phase output signals of the graphic display memory and for providing a single phase serial output signal;

wherein the means for providing a serial output signal includes at least one parallel-to-serial shifter and a data selector.

6. The system of claim 1 wherein the n dots per inch resolution of the original bitonal pixel-code information has an integer relationship to the resolution of the lower resolution pixel-code information.

7. The system of claim 6 wherein the resolution for the original bitonal pixel-code information is either 200, 300, or 400 dots-per-inch and the resolution for the lower resolution pixel-code information is 100 dots-per-inch.

8. The system of claim 1 wherein the means for storing the lower resolution pixel-code information includes a bit-mapped memory.

9. The system of claim 1 including means connected to said decoding means for displaying an enhanced resolution image represented by said output data stream.

10. The system of claim 1 wherein for each gray level in said subset of gray levels said corresponding gray scale value is approximately equal to an average value of said corresponding plurality of special pixel values.

11. An image-processing system for converting a higher-resolution bitonal bit image representation to lower-resolution pixel-code information retaining in decodable form certain predetermined high resolution features of the bitonal bit image representation suitable for display, the system comprising:

means for receiving original bitonal pixel-code information from a document scanned with a resolution of n dots-per-inch and for converting the original bitonal pixel-code information to lower resolution pixel-code information, where the resolution of the lower resolution pixel-code information is less than n dots-per-inch, the lower resolution pixel-code information including a first set of code values representing m-gray levels and a second set of code values, said second set being a subset of said first set wherein each code value in said second set has a corresponding plurality of special pixel values, whereby said special pixel values serve to duplicate said predetermined high resolution features;

wherein the means for converting includes means for assigning one of said first set of code values to a pixel in said lower resolution pixel-code information based upon pixel-codes in a cluster of pixels in said original bitonal pixel-code information which corresponds to said pixel;

means for storing the lower resolution pixel-code information, wherein the means for storing the lower resolution pixel-code information includes a bit-mapped memory;

means for decoding the stored lower resolution pixel-code information to produce an output data stream for display;

wherein the means for decoding includes means for splitting all said pixels into two or more twixels in the output data stream;

wherein said means for decoding also includes means for recognizing the code values belonging to both said first and second sets and for reconstructing the predetermined high resolution features of the bitonal coded pixel-code information using the plurality of special pixel values corresponding to each of said recognized code values, wherein each pixel having a code value belonging only to said first set is split into twixels with the same gray level and wherein each pixel having a code value belonging to both said first and said second sets is split into twixels with different gray levels, each gray level being selected from said corresponding plurality of special pixel values, so as to duplicate the certain predetermined high resolution features of the original bitonal pixel-code information; and

means connected to said decoding means for displaying an enhanced resolution image represented by said output data stream.

12. The system of claim 11 wherein the means for storing the lower resolution pixel-code information includes a graphic display memory having two-phase output signals;

wherein the means for decoding includes data decoding logic means for receiving the two-phase output signals of the graphic display memory and for providing a single phase serial output signal;

said means for providing a serial output signal including two parallel to serial shifters and a data selector.

13. The system of claim 11 wherein pixels are split into horizontally spaced twixels thereby increasing the horizontal resolution of the displayed images.

14. A method of converting a higher-resolution bitonal bit image representation to lower-resolution pixel-code information retaining in decodable format certain predetermined high resolution features of the bitonal bit image representation suitable for display, the method comprising the steps of:

converting a high resolution bitonal bit map from a scanned document into a coded lower resolution bit map;

wherein said converting step includes selecting a gray scale having m gray levels for said coded lower resolution bit map;

approximating said predetermined high resolution features including the substeps of selecting a subset of said m gray levels and selecting, for each gray level in said subset, a corresponding plurality of special pixel values;

wherein said converting step further includes selecting a cluster of pixels from said high resolution bitonal bit map, selecting one of said m gray levels based upon pixels in said selected cluster and assigning said selected gray level to a pixel in said coded lower resolution bit map which corresponds to said selected cluster;

storing the coded lower resolution pixel-code information;

decoding the coded lower resolution bitmap to produce an output data stream for display;

wherein said decoding step includes recognizing gray levels belonging to said subset of gray levels and reconstructing the predetermined high resolution features of the bitonal bitmap using the special pixel values corresponding to said recognized gray levels; and

displaying an enhanced resolution image represented by the output data stream.

15. The method of claim 14 wherein the decoding step includes splitting all pixels into two or more twixels.

16. The method of claim 15 wherein for each pixel having a gray level that does not belong to said subset of gray levels, said step of splitting includes providing, for each of said two or more twixels, said gray level to said output data stream;

and wherein for each pixel having a gray level that is recognized as belonging to said subset of gray levels, said step of splitting includes, for each of said two or more twixels, selecting from the plurality of special pixel values corresponding to said recognized gray level one of said special pixel values and providing said selected special pixel value to said output data stream.

17. The method of claim 14 wherein the step of storing the coded lower resolution bitmap includes storing in a graphic display memory having two-phase output signals;

wherein the step of decoding includes data decoding the two-phase output signals of the graphic display memory and providing a single phase serial output signal using two parallel to serial shifters and a data selector.

18. The method of claim 14 wherein said approximating includes identifying specific pixel configurations in said clusters of said high resolution bitonal bit map, and basing said substeps of selecting a subset of m gray levels and selecting said corresponding special pixel values upon said specific pixel configurations.