Period-based bit conversion method and apparatus for digital image processing

• US 6,292,168 B1
• Filed: 08/13/1998
• Issued: 09/18/2001
• Est. Priority Date: 08/13/1998
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Fleckenstein, Patrick A. Jr., Fuss, William A., Venable, Dennis L.
• Primary Examiner(s): Luu, Matthew
• Assistant Examiner(s): Sajous, Wesner
• Application Number:
  US09/133,565
• Time in Patent Office: 1,132 Days
• Field of Search: G09/G.102, 345/132, 345/153, 345/154, 345/155, 345/152, 345/190, 382/244, 382/245, 382/246, 382/247, 382/1.2, 382/41, 341/50-56, 341/63, 341/2
• US Class Current: 345/605
• CPC Class Codes: G06T 3/40 Scaling of whole images or parts thereof, e.g. expanding or contracting
• CPC Class Codes: G09G 2340/0428 Gradation resolution change

Abstract

A period-based method for converting digital image data for a plurality of pixels from a first bit depth to a second bit depth includes receiving an input scanline of an arbitrary length comprising digital image data for a plurality of input image pixels. Each of the input image pixels is defined at the first bit depth. The input scanline is divided into a plurality of periods each comprising digital image data for a select number of input image pixels. The period is selected so that the image data for the select number of input image pixels exactly comprises m bytes when defined at the first bit depth and exactly comprises n bytes when defined at the second bit depth, wherein m and n are different integers. For each of the periods in succession, the image data for each of the select number of input image pixels is converted from the first bit depth to the second bit depth. A code generator generates hard-coded conversion operating instructions and a look-up table for specified bit conversion operations and generic conversion operating instructions for all other bit conversion operations.

Claims

1. A period-based method of converting digital image data for a plurality of pixels from a first bit depth to a second bit depth, said method comprising:

a) receiving an input scanline of an arbitrary length comprising digital image data for a plurality of input image pixels, each of said plurality of input image pixels defined at a first bit depth;

b) dividing the input scanline into a plurality of periods and a remainder with each of said plurality of periods comprising digital image data for a select number of input image pixels and said remainder comprising digital image data for less than said select number of input image pixels, said select number of input image pixels defining a period selected so that the image data for the select number of input image pixels exactly comprises m bytes when defined at the first bit depth and exactly comprises n bytes when defined at a second bit depth, wherein m and n are different integers;

c) for each of said plurality of periods in succession, converting the image data for each of said select number of input image pixels from the first bit depth to the second bit depth; and

,

d) converting the image data defining said remainder from the first bit depth to the second bit depth.

6. The method of converting digital image data as set forth in claim 1, further comprising:

before step a), reading an input file comprising a list of specified bit conversion operations;

for each of said specified bit conversion operations, writing bit conversion instructions for calculating the number of input image pixels in each of said periods, for extracting image data for each input image pixel from each period, and, for accessing a look-up table to obtain output image data at the second bit depth for each input image pixel.

2. A period-based method of converting digital image data for a plurality of pixels from a first bit depth to a second bit depth said method comprising:

a) receiving an input scanline of an arbitrary length comprising digital image data for a plurality of input image pixels, each of said plurality of input image pixels defined at the first bit depth;

b) dividing the input scanline into a plurality of periods each comprising digital image data for a select number of input image pixels, said period selected so that the image data for the select number of input image pixels exactly comprises m bytes when defined at the first bit depth and exactly comprises n bytes when defined at a second bit depth wherein m and n are different integers and wherein said select number of input image pixels in said period is determined according to the following;

$p<br><br>\mathrm{\_in}=\frac{\mathrm{input\_block}<br><br>\mathrm{\_size}}{\gcd <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{input\_block}<br><br>\mathrm{\_size},c\right)}$$p<br><br>\mathrm{\_out}=\frac{\mathrm{output\_block}<br><br>\mathrm{\_size}}{\gcd <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{output\_block}<br><br>\mathrm{\_size},x\right)}$$\mathrm{Input}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Pixels}<br><br>\text{\hspace{1em}<br><br>}<br><br>P/\mathrm{Period}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z=\mathrm{lcm}<br><br>\left(p<br><br>\mathrm{\_in},p<br><br>\mathrm{\_out}\right)$

input_block_size=the natural word size of the input pixel data,

output_block_size=the natural word size of the output pixel data,

gcd=greatest common denominator operation,

lcm=lowest common multiple operation,

c=the input bit depth, and,

x=the output bit depth; and

,

c) for each of said plurality of periods in succession, converting the image data for each of said select number of input image pixels from the first bit depth to the second bit depth.

3. The method of converting digital image data as set forth in claim 2, wherein the input block_size is one of 8 bits and 16 bits in length and wherein the output_block_size is one of 8 bits and 16 bits in length.

4. The method of converting digital image data as set forth in claim 2, wherein said step of converting the image data for each of said input image pixels from the first bit depth to the second bit depth comprises:

sequentially extracting the image data for each of said input image pixels; and

,

indexing a look-up table with the extracted image data to obtain output image data from said look-up table corresponding to the extracted image data at the second bit depth.

5. The method of converting digital image data as set forth in claim 2, further comprising:

d) converting image data for each remainder input image pixel not included in one of the plurality of periods.

7. An apparatus for converting digital image data from a first bit depth to a second bit depth, said apparatus comprising:

means for supplying an input scanline of image data representing an plurality of input image pixels at the first bit depth;

means for dividing the image data of the input scanline into a plurality of equal periods each comprising image data for a select number of input image pixels, the select number of input image pixels per period determined according to the following;

$p<br><br>\mathrm{\_in}=\frac{\mathrm{input\_block}<br><br>\mathrm{\_size}}{\gcd <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{input\_block}<br><br>\mathrm{\_size},c\right)}$$p<br><br>\mathrm{\_out}=\frac{\mathrm{output\_block}<br><br>\mathrm{\_size}}{\gcd <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{output\_block}<br><br>\mathrm{\_size},x\right)}$$\mathrm{Input}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Pixels}<br><br>\text{\hspace{1em}<br><br>}<br><br>P/\mathrm{Period}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z=\mathrm{lcm}<br><br>\left(p<br><br>\mathrm{\_in},p<br><br>\mathrm{\_out}\right)$

wherein;

input_block_size the natural word size of the input pixel data,

output_block_size=the natural word size of the output pixel data,

gcd=greatest common denominator operation,

lcm=lowest common multiple operation,

c=the input bit depth, and,

x=the output bit depth;

means for accessing the image data of each of said plurality of periods of said input scanline image data and for converting the image data for each input image pixel from the first bit depth to image data for an output image pixel at the second bit depth; and

,

means for storing the image data for each output image pixel in an output scanline at the second bit depth.

8. The apparatus as set forth in claim 7, further comprising:

means for accessing input image data for at least one remainder input image pixel of said input scanline not included in said plurality of periods and for converting said input image data for said at least one remainder input image pixel from the first bit depth to output image data the second bit depth; and

,

means for storing the output image data in the output scanline.

9. The apparatus as set forth in claim 7, further comprising:

means for accessing an input file including a list of select bit conversion operations;

means for generating specific operating instructions for each of the select bit conversion operations; and

,

means for generating a look-up table for each of said select bit conversion operations for interrelating input image data having the first bit depth to output image data having the second bit depth.

10. The apparatus as set forth in claim 9, wherein said means for generating specific operating instructions for each of the select bit conversion operations generates at least operating instructions for performing required shifting and masking operations to extract image data for said plurality of input image pixels from said input image scanline.

11. A method of converting digital image data from a first bit depth of c bits per pixel to a second bit depth of x bits per pixel, wherein c and x are integers, said method comprising:

a) receiving input image data for a plurality of input pixels at the first bit depth;

b) selecting a plurality of input pixels of said input image exactly comprising an n byte period so that said image data for said period of input pixels, when converted to output image data having the second bit depth, exactly comprises m bytes of output image data, wherein m and n are integers and wherein said period of n bytes of said input image data is determined according to the following;

$p<br><br>\mathrm{\_in}=\frac{\mathrm{input\_block}<br><br>\mathrm{\_size}}{\gcd <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{input\_block}<br><br>\mathrm{\_size},c\right)}$$p<br><br>\mathrm{\_out}=\frac{\mathrm{output\_block}<br><br>\mathrm{\_size}}{\gcd <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{output\_block}<br><br>\mathrm{\_size},x\right)}$$\mathrm{Input}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Pixels}<br><br>\text{\hspace{1em}<br><br>}<br><br>P/\mathrm{Period}<br><br>\text{\hspace{1em}<br><br>}<br><br>Z=\mathrm{lcm}<br><br>\left(p<br><br>\mathrm{\_in},p<br><br>\mathrm{\_out}\right)$

input_block_size=the natural word size of the input pixel data,

output_block_size=the natural word size of the output pixel data,

gcd=greatest common denominator operation,

lcm=lowest common multiple operation,

c=the input bit depth, and,

x=the output bit depth

c) converting the input image data for each of said input pixels in said period from the first bit depth to the second bit depth; and

,

d) repeating steps b)-c) for all n byte periods of said input image data so that the input image data included in each period is converted from the first bit depth to the second bit depth.

12. The method of converting digital image data as set forth in claim 11, further comprising:

e) for all remainder input image data not included in one of said n byte periods, converting said remainder input image data from said first bit depth to said second bit depth.

13. The method of converting digital image data as set forth in claim 11, wherein said input_block_size and said output_block_size are each one of 8 bits and 16 bits.