Image analysis – Color image processing
Reexamination Certificate
1999-01-18
2001-08-14
Tran, Phuoc (Department: 2621)
Image analysis
Color image processing
C382S167000
Reexamination Certificate
active
06275605
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of digital image processing and, more particularly, to a method for adjusting the tone scale of a digital image.
BACKGROUND OF THE INVENTION
Existing methods for applying tone scales to digital color images include applying the tone scale to each of the color channels independently, applying the tone scale to the neutral channel and preserving the original pixel color difference signal, or applying the tone scale to just the low frequency image. These methods of tone scale application alter the sharpness and appearance of the color in processed images, and the latter can produce displeasing artifacts.
Traditional methods of applying a tone scale function to a digital color image modify the apparent sharpness of the image because the tone scale modifies the amplitudes of high frequency detail information. This phenomenon occurs when the tone scale function is applied to each of the color channels independently, or when the tone scale function is applied to the neutral channel and original pixel color difference signals are preserved.
In an effort to apply a tone scale function to a digital image without distorting the detail information, in U.S. Pat. No. 5,012,333, Lee et al. proposed separating the image into a high frequency and a low frequency image by using FIR filters. The tone scale function is then applied to only the low frequency image, and the high frequency image is added back to the tone scaled low frequency image.
Also, in U.S. Pat. No. 5,454,044, Nakajima suggests modifying the image contrast by the formula
S
proc=
S
org+
f
(
Sus
).
The low frequency image (Sus) is passed through function f( ) which is a monotonically decreasing function. This signal is added to the original (Sorg) to create the processed image Sproc.
Both of these methods preserve the high frequencies of the image, but both may lead to the creation of unsharp mask type artifacts (overshoot and undershoot) in the neighborhood of large edges (characteristic of occlusion boundaries or dark shadows).
Although the presently known and used methods for adjusting the tone scale of a digital image are satisfactory, they include the above-described drawbacks. The present invention permits the application of a tone scale function to a digital image which adjusts the macro contrast of the image, preserves the high frequency detail information, and prevents artifacts in the neighborhood of large edges.
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 adjusting tone scale of a digital image, the method comprising: (a) receiving a digital image channel from the digital image; (b) providing a tone scale function for adjusting the tone scale of the digital image channel; (c) calculating a difference signal derived from the digital image channel and the tone scale function; (d) calculating a compensation signal derived from a filtered version of the difference signal; and (e) combining the digital image channel and the compensation signal to generate a modified digital image channel.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
ADVANTAGEOUS EFFECT OF THE INVENTION
The present invention has the advantage of permitting the application of a tone scale function to a digital image that adjusts the macro contrast of the image, while preserving the spatial frequency detail information, without introducing artifacts in the neighborhood of large transitions.
REFERENCES:
patent: 5012333 (1991-04-01), Lee et al.
patent: 5060061 (1991-10-01), Shishido et al.
patent: 5164993 (1992-11-01), Capozzi et al.
patent: 5454044 (1995-09-01), Nakajima
patent: 5633511 (1997-05-01), Lee et al.
Gallagher Andrew C.
Gindele Edward B.
Alavi Amir
Eastman Kodak Company
Tran Phuoc
Woods David M.
LandOfFree
Method for adjusting the tone scale of a digital image does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for adjusting the tone scale of a digital image, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for adjusting the tone scale of a digital image will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2442928