Image analysis – Histogram processing – For setting a threshold
Reexamination Certificate
1999-11-15
2004-05-04
Wu, Jingge (Department: 2723)
Image analysis
Histogram processing
For setting a threshold
Reexamination Certificate
active
06731798
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of medical diagnostic systems, such as imaging systems. More particularly, the invention relates to a technique for converting digital image pixel values.
Discrete imaging devices, such as digital X-ray imaging systems, employ a detector which divides regions of an image into individual picture elements, or pixels. The array or matrix of pixels defines, when viewed as an overall image, features of interest, such as internal anatomy of a subject positioned adjacent to the detector. To facilitate interpretation by physicians and technicians, the individual intensities of the pixels typically define the features of the image by imitating contrasts and textures obtainable through conventional film-based X-ray or imaging systems.
To convert the detected pixel intensities to digitized values suitable for display, the pixel intensity values are processed after acquisition by the detector. In a first stage, the detected pixel intensities are digitized in values which vary over a predetermined dynamic range of the detector and acquisition circuitry, such as 12 to 14 bits. In X-ray systems, for example, these digitized values are representative of the quantity of X-rays received by each pixel during data acquisition. Subsequently, the pixel intensity values are scaled to map the values onto the dynamic range of a display device. As part of this scaling, it is common to perform logarithmic transformation of the image pixel values to obtain a resulting image which mimics conventional film-rendered images. In addition, the scaling process maps the dynamic range of the detector and acquisition circuitry onto the dynamic range of the display. The latter range may be substantially different from that of the upstream circuitry, such as on the order of 8 to 10 bits.
While the logarithmic transformation of the digitized pixel values is useful in rendering an image which is understandable by attending physicians and technicians, performing the transformation prior to the dynamic range scaling can be problematic. For example, histograms are often employed to analyze pixel intensity values. However, processing of histograms generated based on the transformed values can result in difficulties in identifying high and low limits of relevant portions of the detected data, rendering the dynamic range scaling difficult. The use of logarithmically transformed data prior to dynamic range scaling can also result in loss of accuracy for individual pixels in the image matrix.
There is a need, therefore, for an improved method for processing discrete image data that facilitates use of as much of the dynamic ranges of acquisition circuitry and display circuitry as possible. In particular, there is a need for an improved method for converting digital pixel values defining a discrete pixel image from a first dynamic range to a second dynamic range in a computationally efficient manner.
Solutions to the problems described above have not heretofore included significant remote capabilities. In particular, communication networks, such as, the Internet or private networks, have not been used to provide remote services to such medical diagnostic systems. The advantages of remote services, such as, remote monitoring, remote system control, immediate file access from remote locations, remote file storage and archiving, remote resource pooling, remote recording, remote diagnostics, and remote high speed computations have not heretofore been employed to solve the problems discussed above.
Thus, there is a need for a medical diagnostic system which provides for the advantages of remote services and addresses the problems discussed above. In particular, there is a need for improved methods of processing discrete image data which provide for remote services and functionalities, such as, remote diagnostics, transmission of image data over networks, and data storage in remote locations.
SUMMARY OF THE INVENTION
One embodiment of the invention relates to a method for converting digitized image pixel values from a first range to a second range including (a) determining a lower limit value of a relevant portion of the first range; (b) generating an intensity histogram representative of pixel populations having specified intensities, and transforming the histogram to generate a log-transformed histogram; (c) identifying a threshold value for an upper limit of log-transformed values from the log-transformed histogram; (d) identifying a population of pixels having log-transformed values having a desired relationship to the threshold value; (e) determining an upper limit value of the relevant portion of the first range based upon the identified population; (f) converting the pixel values to converted values over the second range based upon the lower and upper limit values; and (g) transmitting information relating to an image associated with the pixel values or sources thereof between a first location and a second location remote from the first location to provide remote services.
Another embodiment of the invention relates to a method for converting digitized image pixel values from an input dynamic range to an output dynamic range including (a) generating a first histogram of the pixel values; (b) identifying a lower limit value from the first histogram; (c) generating a second histogram of log-transformed values of the pixel values by transformation of the first histogram; (d) identifying a population of pixels having desired log-transforned values from the second histogram; (e) identifying an upper limit value from the first histogram based upon the identified population; (f) converting the pixel values from the input range to converted values over the output range based upon the lower and upper limit values;
and (g) transmitting information relating to an image associated with the pixel values or sources thereof between a first location and a second location remote from the first location to provide remote services.
Another embodiment of the invention relates to a method for determining a useful range of image pixel intensity values in a digital pixel imaging system including (a) determining a lower limit value of the useful range by identifying an intensity value below which values of a desired fractional portion of the pixels fall; (b) generating an intensity histogram and a log-transformed histogram based upon the intensity histogram; (c) identifying a threshold value for an upper limit value based upon the log-transformed histogram; (d) identifying a population of pixels having log-transformed values having a desired relationship to the threshold value; (e) determining an upper limit value of the useful range based upon the identified population; and (f) transmitting information relating to the imaging system or an image associated with the pixels between a first location and a second location remote from the first location to provide remote services.
Other principle features and advantages of the present invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.
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Schwenker et al.,Automatic Detection of the Useful Image Data From Digital X-ray Detectors, Society for Photo-Optical Instrumentation Engineering, vol. 3031, pp. 204-209, 1997.
Fletcher Yoder
General Electric Company
Wu Jingge
LandOfFree
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