Method and system for the reduction of memory capacity...

Details Method and system for the reduction of memory capacity... Method and system for the reduction of memory capacity...

1998-05-04

2001-02-06

Tran, Phuoc (Department: 2721)

Image analysis

Histogram processing

C382S169000, C382S251000, C382S274000

Reexamination Certificate

active

06185327

ABSTRACT:

APPENDIX
The disclosure in the appendix of this patent disclosure of this patent document contains material to which a claim of copyright protection is made. The copyright owner has no objection to the facsimile reproduction of any one of the patent documents or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but reserves all other rights whatsoever.
FIELD OF INVENTION
The invention relates generally to the field of digital image compression and, more particularly, to such compression that maintains details of high-contrast portions of a digital image by creating a unique compression method for each image.
BACKGROUND OF THE INVETION
The storage of high resolution digital images within a digital still camera system typically requires substantial memory. For a single sensor camera, a typical image with a resolution of 768 pixels per line ×512 lines ×10 bits per pixel would require 3,932,160 bits or, equivalently, 491,520 bytes of semiconductor memory storage space. If, for system requirements, each 10 bit pixel value must be stored in a 16 bit word of memory (wasting 6 bits per word), the required amount of memory to store the entire image increases to 786,432 bytes. If the data could be transformed in some reversible manner to require only 8 bits (1 byte) per pixel, without significantly degrading image quality, then only 393,216 bytes of memory are required for a 50% savings of storage memory.
Logarithm transforms have been used in the past to transform ten bit pixel values into eight bit pixel values. Typically one would use an expression such as Equation 1 to map 10 bit linear exposure data into 8 bit logarithmic exposure data.
y
=
round
⁢
 
[
25.5
log
10
⁡
(
2
)
⁢
 
⁢
log
10
⁡
(
x
+
1
)
]
,
0
≤
x
≤
1023
(
1
)
In Equation 1,“x” is the 10 bit linear exposure value, “y” is the corresponding 8 bit logarithmic value and “round” rounds the result to the nearest integer. Equation 1 can be inverted to produce Equation 2 for transforming a 8 bit logarithmic value to a ten bit linear exposure value.
x
=
round
⁢
 
[
 
⁢
antilog
10
⁡
(
log
10
⁡
(
2
)
25.5
⁢
 
⁢
y
)
-
1
]
,
0
≤
y
≤
255
(
2
)
Although the presently known and utilized method for data transformation is satisfactory, it is not without drawbacks. The present digital compression does not account for the scene contents of the image so that details in high contrast areas may be lost if the code values in this area are quantized to a narrow range of output code values.
Consequently, a need exists for a method and apparatus for the compression of imaging data for overcoming the above-described drawbacks.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, the invention resides in a method for reducing a bit depth of an image to reduce storage memory, the method comprising the steps of: (a) creating a histogram of an image; (b) modifying the histogram so that a maximum slope of a to-be-calculated cumulative histogram will be no greater than substantially 1.0; (c) calculating the cumulative histogram from the modified histogram; and (d) interpreting the cumulative histogram to give a desired bit depth reduction.
ADVANTAGEOUS EFFECT OF THE INVENTION
The present invention has the following advantages of providing customized compression for each image so that scene content is not degraded.


REFERENCES:
patent: 5410617 (1995-04-01), Kidd et al.
patent: 5426517 (1995-06-01), Schwartz
patent: 6038341 (2000-03-01), Takeshima et al.
patent: 6091853 (2000-07-01), Otto

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