Image analysis – Image enhancement or restoration – Intensity – brightness – contrast – or shading correction
Reexamination Certificate
1999-11-24
2003-09-30
Ahmed, Samir (Department: 2723)
Image analysis
Image enhancement or restoration
Intensity, brightness, contrast, or shading correction
C358S461000
Reexamination Certificate
active
06628843
ABSTRACT:
CROSS REFERENCE TO RELATED U.S. PATENTS
Cross reference is made to the following commonly assigned U.S. Patents to Eschbach et al., each of which is hereby expressly incorporated by reference herein: U.S. Pat. No. 5,414,538; U.S. Pat. No. 5,357,352; U.S. Pat. No. 5,450,502; U.S. Pat. No. 5,371,615; U.S. Pat. No. 5,363,209; U.S. Pat. No. 5,450,217; and, U.S. Pat. No. 5,802,214. Similarly, commonly assigned U.S. Pat. No. 5,347,374 to Fuss et al. is also hereby expressly incorporated by reference herein.
BACKGROUND OF THE INVENTION
In the past, a typical application for copiers or scan-to-print image processing systems was to reproduce an input image as accurately as possible, i.e., render a copy. Thus, copies have been rendered as accurately as possible, including flaws in the source image. However, as customers have become more sophisticated in their document reproduction requirements, they have recognized that an exact copy is often not desired. Instead, an inexact copy that is perceived as a higher quality image has been deemed more desirable.
Until recently, image quality from the output of a copier or a scan-to-print system was directly related to the quality of the input image. While this has been satisfactory for reproducing images of text or line drawings, it has been found to be sub-optimal for purposes of reproducing photographs and other more complex images. With photographs, in particular, reproduction is complicated given the inexact nature of the discipline, variations in equipment, aging of photographs, and the like. Given that the input image is often poor quality, it has been deemed desirable to render an output image that is perceived to be the “best” possible image (or at least superior to the input image), rather than an exact copy.
The above-noted patents to Eschbach et al. and Fuss et al. disclose an Automated Image Enhancement (AIE) system. This system receives an optionally sub-sampled description of the input image, and alters the tone reproduction curve (TRC)—a curve that defines the relationship of an input image signal to an output image signal for purposes of enhancement—and/or derives or alters a sharpness filter for that image on an image-by-image basis, as appropriate, so that the resulting output image is perceived to be superior to the input image. AIE is used, for example, to alter perceived exposure, luminance, sharpness, saturation, color balance, and the like to provide an output image that is preferable to the input image. It is important to note that AIE performs well even if it has to rely upon a sub-sampled image to statistically analyze the overall image. AIE does not require that each and every item of image information be analyzed. Of course, this sub-sampling speeds image enhancement operations and reduces the size
umber of memory buffers required to implement the AIE system.
More particularly, for example, U.S. Pat. No. 5,414,538 entitled “Image-Dependent Exposure Enhancement” discloses a method of altering the perceived exposure of an output image produced from an input image that includes: (a) receiving the input image defined in terms of red-green-blue (RGB) signals; (b) converting the RGB signals to corresponding luminance-chrominance signals including at least one signal that represent overall image intensity; (c) comparing the intensity signal to upper and lower intensity threshold signals that define the acceptable levels of brightness and darkness in the image; (d) if one of the thresholds is exceeded, the image signal representative of image intensity is processed according to a select equation, and a TRC associated with the image is adjusted so that exposure characteristics of the resulting output image are perceived to be superior to those of the input image.
U.S. Pat. No. 5,450,502 entitled “Image-Dependent Luminance Enhancement” discloses a method of altering the perceived luminance of an output image produced from an input image that includes: (a) receiving the input image data defined in terms of a color space; (b) if required, converting the input image data into a luminance-chrominance color space wherein at least one term bears a relationship to overall intensity of the input image; (c) deriving a global intensity histogram for the overall input image; (d) filtering the histogram signal to flatten high peaks and low valleys without altering its relatively flat portions; and, (e) utilizing the filtered histogram signal to control TRC mapping in a device with which the image is to be rendered. In accordance with another aspect of the disclosed luminance enhancement method, the input image can be divided into plural regions, and a local intensity histogram signal can be derived for each region. If any of the local histogram signals are flatter than the global histogram signal, the local signals are summed and used in place of the global histogram as input to the histogram flattening filter.
The methods described in the Eschbach et al. '538 and '502 patents, and the other Eschbach et al. and Fuss et al. patents noted above, are described in connection with uncompressed image data. However, in many image processing operations, the image data is retrieved from an image storage device or other location or is otherwise supplied in a compressed form to minimize image storage space. Most commonly, the image data is compressed according to the Joint Photographic Expert Group (JPEG) recommendation ISO DIS 10918-1 that has become an international standard for lossy compression of still images.
Thus, heretofore, image enhancement operations according to the AIE systems described above have required that the JPEG (or otherwise) compressed images first be decompressed or “decoded” for image enhancement operations. This is undesirable in that the decompression operation slows the overall enhancement operation, the image processing apparatus must be provided with additional memory to accommodate large amounts of uncompressed image data, and each JPEG or other lossy compression operation, itself, further degrades the image data due to data loss.
In light of the foregoing, it has been deemed desirable to provide a novel and non-obvious method for utilizing JPEG compressed image data in the image enhancement operations described in the above-noted Eschbach et al. and Fuss et al. AIE patents. This will allow JPEG compressed images to be enhanced for subsequent rendering without the image being decompressed, enhanced, and then recompressed.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and apparatus for image enhancement of JPEG compressed image data are provided.
In accordance with a first aspect of the present invention, a method of processing JPEG compressed image data comprises: (i) receiving JPEG compressed image data that represent an input digital image, the JPEG compressed image data including a plurality of DC components; (ii) extracting a plurality of the DC components from the JPEG compressed image data; (iii) inputting at least some of the extracted DC components to an automated image enhancement system; (iv) using the DC components input to the automated image enhancement system to derive a final correction tone reproduction curve and/or a sharpness filter for enhancement of the input digital image represented by the JPEG compressed data; (v) decompressing the JPEG compressed image data to obtain decompressed image data that represent the input digital image; and, (vi) using the final tone reproduction curve and/or the sharpness filter to enhance the decompressed image data.
In accordance with another aspect of the present invention, an apparatus for processing JPEG compressed image data is provided. The apparatus includes means for receiving JPEG compressed image data that represent an input digital image; a DC component extractor adapted for extracting a plurality of the DC components from the JPEG compressed image data; an automated image enhancement system adapted for receiving some or all of the extracted DC components and for using same to derive a final correction tone reprodu
Eschbach Reiner
Knox Keith T.
Ahmed Samir
Fay Sharpe Fagan Minnich & McKee LLP
Xerox Corporation
LandOfFree
Image enhancement on JPEG compressed image data does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image enhancement on JPEG compressed image data, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image enhancement on JPEG compressed image data will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3098680