Method and apparatus for compressing and expanding image data

• US 6,633,675 B1
• Filed: 08/22/2000
• Issued: 10/14/2003
• Est. Priority Date: 08/23/1999
• Status: Expired due to Fees

• Current Assignee: PENTAX RICOH IMAGING COMPANY, LTD.
• Original Assignee: Pentax Corporation (Hoya Corporation)
• Inventors: Abe, Nobuaki
• Primary Examiner(s): Johns, Andrew W.
• Assistant Examiner(s): Alavi, Amir
• Application Number:
  US09/642,814
• Time in Patent Office: 1,148 Days
• Field of Search: 382/184, 382/239, 382/232, 382/233, 382/287, 382/295, 382/296, 382/297, 382/298, 382/299, 382/300, 345/648, 345/659, 345/660, 345/671, 345/672, 345/677, 348/449, 348/561, 348/581, 348/583, 348/704, 358/428, 358/451, 358/488, 358/525, 708/203, 708/208, 708/290
• US Class Current: 382/232
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00

Abstract

A compression apparatus transforms original image data partitioned into first blocks, each of which is composed of a plurality of pixels, to reduced-image data composed of a smaller number of pixels than that of the original image data. The reduced-image data is subjected to a fluency transform to generate expanded-image data partitioned into second blocks corresponding to the first blocks. The fluency transform has a plurality of modes, and one mode is selected from the plurality of modes, thus the expanded-image data is generated in accordance with the selected one mode. An error, which represents a difference between the original image data and the expanded-image data, is calculated in each of the plurality of modes. Then, an optimum mode, by which the error becomes a minimum value, is determined among the plurality of modes. On the other hand, an expansion apparatus generates the expanded-image data by applying the fluency transform using the optimum mode.

Claims

1. A compression apparatus for compressing image data comprising:

a reduced-image generating processor that transforms original image data partitioned into first blocks, each of which is composed of a plurality of pixels, to reduced-image data composed of a smaller number of pixels than that of said original image data;

a fluency transform processor that applies a fluency transform to said reduced-image data to generate expanded-image data partitioned into second blocks corresponding to said first blocks, said fluency transform having a plurality of modes;

a mode setting processor that selects one mode from said plurality of modes, said expanded-image data being generated in accordance with said selected one mode;

an error calculating processor that calculates an error, which represents a difference between said original image data and said expanded-image data, said error calculating processor calculating said error in each of said plurality of modes; and

an optimum mode determining processor that determines an optimum mode, by which said error becomes minimum, among said plurality of modes.

2. The compression apparatus according to claim 1, further comprising a recording medium, said reduced-image data and said optimum mode being recorded in said recording medium.

3. The compression apparatus according to claim 1, wherein each of said first blocks and each of said second blocks are composed of 8×

8 (=64) pixels respectively.

4. The compression apparatus according to claim 1, wherein said reduced-image generating processor generates said reduced-image data composed of average pixels, obtained by finding an average value of said plurality of pixels in each of said first blocks.

5. The compression apparatus according to claim 1, wherein said fluency transform processor generates said expanded-image data by applying the fluency transform, which is expressed by the following formula, to each pixel of said reduced-image data:

$f<br><br>\left(t\right)=\left(1/2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\pi <br><br>}\right)<br><br>{\int <br><br>}_{-\mathrm{\pi <br><br>}}^{\mathrm{\pi <br><br>}}<br><br>{F<br><br>\left(u\right)}_{\left[\begin{array}{cc}m& \text{\hspace{1em}<br><br>}\\ \text{\hspace{1em}<br><br>}& o\end{array}\right]}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\phi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(t,u\right)<br><br><br><br>u$

note that, $\begin{array}{c}{\hspace{0.17em}<br><br>}_{\left[\begin{array}{cc}m& \text{\hspace{1em}<br><br>}\\ \text{\hspace{1em}<br><br>}& o\end{array}\right]}<br><br>\mathrm{\phi <br><br>}<br><br>\left(t,u\right)=\text{\hspace{1em}<br><br>}<br><br>\left(1/2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\pi <br><br>}\right)<br><br>{\int <br><br>}_{-\mathrm{\infty <br><br>}}^{\mathrm{\infty <br><br>}}<br><br>\left\{\underset{p=-\mathrm{\infty <br><br>}}{\overset{\mathrm{\infty <br><br>}}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\delta <br><br>}<br><br>\left(\mathrm{\omega <br><br>}-u+2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>p\right)\right\}\times <br><br>\\ \text{\hspace{1em}<br><br>}<br><br>{\left\{\underset{q=-\mathrm{\infty <br><br>}}{\overset{\mathrm{\infty <br><br>}}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\left(1-q<br><br>\left(2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\pi <br><br>}/\mathrm{\omega <br><br>}\right)\right)}^{-2<br><br>m}\right\}}^{-1/2}\times <br><br>\exp <br><br>\left(\mathrm{<br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)<br><br><br><br>\mathrm{\omega <br><br>}\end{array}$

where F(u) corresponds to each pixel value of said reduced-image data, f(t) is a output values of the fluency transform, φ

(t,u) is the fluency function defined by a fluency function space ^mS, and m (=1,2,3, . . . ) is a parameter indicating a differentiability, said parameter m corresponding to said plurality of modes.

6. The compression apparatus according to claim 5, wherein said fluency transform processor applies the fluency transform in a state such that each pixel of said reduced-image data are arranged at a center position of each of said second blocks, and generates said expanded-image data composed of said plurality of pixels by adding said output values f(t) corresponding to pixel-positions in said second blocks.

7. The compression apparatus according to claim 6, wherein said plurality of pixels in said original image data is arranged in a matrix, and said fluency transform processor applies the fluency transform along a first direction to each pixel of said reduced-image data so that pixels aligned along said first direction are generated, and then applies the fluency transform to said pixels aligned along said first direction, along a second direction perpendicular to said first direction such that said plurality of pixels in each of said second blocks is generated.

8. The compression apparatus according to claim 1, wherein said error calculating processor calculates a difference between each pixel value of said first blocks and each corresponding pixel value of said second blocks, and calculates a sum total of the square of said difference as said error, said optimum mode determining processor setting a mode, which makes said error minimum, among said plurality of modes as said optimum mode.

9. The compression apparatus according to claim 1, wherein said optimum mode is determined in each of said second blocks.

10. An expansion apparatus for expanding said reduced-image data recorded in said recording medium by said compression apparatus in claim 2, said expansion apparatus comprising:

a data reading processor that reads said reduced-image data and said optimum mode recorded in said recording medium;

an optimum mode setting processor that sets said optimum mode among said plurality of modes; and

an expanded-image generating processor that applies said fluency transform based on said optimum mode to said reduced-image data such that expanded-image data corresponding to said original image data is obtained.

11. A compression method for compressing image data comprising:

transforming original image data partitioned into first blocks, each of which is composed of a plurality of pixels, to reduced-image data composed of a smaller number of pixels than that of the original image data;

applying a fluency transform to the reduced-image data to generate expanded-image data partitioned into second blocks corresponding to the first blocks, the fluency transform having a plurality of modes;

selecting one mode from the plurality of modes, the expanded-image data being generated in accordance with the selected one mode;

calculating an error in each of the plurality of modes, the error representing, a difference between the original image data and the expanded-image data;

determining an optimum mode, by which the error becomes minimum, among the plurality of modes; and

recording the reduced-image data and the optimum mode in a recording medium.

12. An expansion method for expanding said reduced-image data obtained by said compression method in claim 11, said expansion method comprising:

reading the reduced-image data and the optimum mode from the recording medium;

setting the optimum mode among the plurality of modes; and

applying the fluency transform based on said optimum mode to the reduced-image data such that expanded-image data corresponding to the original image data is obtained.

13. A memory medium that stores a program for compressing image data, the program comprising:

transforming original image data partitioned into first blocks, each of which is composed of a plurality of pixels, to reduced-image data composed of a smaller number of pixels than that of the original image data;

applying a fluency transform to the reduced-image data to generate expanded-image data partitioned into second blocks corresponding to the first blocks, the fluency transform having a plurality of modes;

selecting one mode from the plurality of modes, the expanded-image data being generated in accordance with the selected one mode;

calculating an error in each of the plurality of modes, the error representing, a difference between the original image data and the expanded-image data;

determining an optimum mode, by which the error becomes minimum, among the plurality of modes; and

recording the reduced-image data and the optimum mode in a recording medium.

14. A memory medium that stores a program for expanding said reduced-image data described in claim 13, comprising:

reading the reduced-image data and the optimum mode from the recording medium;

setting the optimum mode among the plurality of modes; and

applying the fluency transform based on the optimum mode to the reduced-imaged data such that expanded image data corresponding to the original image data is obtained.

15. A compression apparatus for compressing image data comprising:

a reduced-image generating processor that transforms original image data partitioned into first blocks, each of which is composed of a plurality of pixels, to reduced-image data composed of a smaller number of pixels than that of said original image data;

a fluency transform processor that applies a fluency transform to said reduced-image data to generate expanded-image data partitioned into second blocks corresponding to said first blocks, said fluency transform having a plurality of modes;

a contrast coefficient calculating processor that obtains a contrast coefficient in such a manner that a contrast of said expanded-image data becomes close to a contrast of said original image data by applying said contrast coefficient to said expanded-image data;

a contrast transform processor that applies said contrast coefficient to said expanded-image data to modify the contrast of said expanded-image data so that modified expanded-image data is obtained;

a mode setting processor that selects one mode from said plurality of modes, said modified expanded-image data being generated in accordance with said selected one mode;

an error calculating processor that calculates an error, which represents a difference between said original image data and said modified expanded-image data, said error calculating processor calculating in each of said plurality of modes; and

an optimum mode/contrast determining processor that determines an optimum mode, by which said error becomes minimum, among said plurality of modes, and then sets a contrast coefficient corresponding to said optimum mode as an optimum contrast coefficient.

16. The compression apparatus according to claim 15, wherein said contrast transform modifies said expanded-image data such that a pixel having a relatively high contrast in said expanded-image data is modified to a higher contrast pixel, and a pixel having a relatively low contrast in said expanded-image data is modified to a lower contrast pixel.

17. The compression apparatus according to claim 15, wherein said contrast coefficient calculating processor obtains said contrast coefficient, which makes a sum of the square of the difference between each pixel value of said original image data and each corresponding pixel value of said modified expanded-image data.

18. The compression apparatus according to claim 15, further comprising a recording medium, said optimum contrast coefficient and said optimum mode, said reduced-image data, said optimum contrast coefficient and said optimum mode being recorded in said recording medium.

19. An expansion apparatus for expanding said reduced-image data recorded in said recording medium by said compression apparatus for compressing the image data in claim 18, said expansion apparatus comprising:

a data reading processor that reads said reduced-image data, said optimum contrast coefficient and said optimum mode recorded in said recording medium;

an optimum mode setting processor that sets said optimum mode among said plurality of modes;

an expanded-image generating processor that applies said fluency transform according to said optimum mode to said reduced-image data such that expanded-image data corresponding to said original image data is obtained; and

a contrast modifying processor that applies said contrast transform based on said optimum contrast coefficient to said expanded-image data, to obtain modified expanded-image data.