Method and Apparatus for Calibration and Correction of Gray Levels in Images

• US 20080205738A1
• Filed: 05/06/2008
• Published: 08/28/2008
• Est. Priority Date: 02/14/2003
• Status: Active Grant

• Current Assignee: Fanny Jeunehomme, Razvan Iordache, Serge Muller
• Original Assignee: Fanny Jeunehomme, Razvan Iordache, Serge Muller
• Inventors: Muller, Serge, Iordache, Razvan, Jeunehomme, Fanny
• Granted Patent: US 7,548,640 B2
• Time in Patent Office: Days
• US Class Current: 382/132
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/30004 Biomedical image processing
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction
• CPC Class Codes: H04N 5/32 Transforming X-rays cameras or camera modules for generating image signals from X-rays H04N23/30; circuitry of SSIS for transforming X-rays into image signals H04N25/30

Abstract

A method and apparatus for calibrating an apparatus that acquires a sequence of radiographic images and correcting images of an object under observation. For each image of a sequence acquired by the apparatus and for a given frequency of acquisition of the sequence, the apparatus is calibrated by determining the value of the variation of a mean of gray levels in at least one zone of interest of the current image of at least one calibration device, the variation being determined relative to the mean gray level of the first image of the sequence in each zone of interest. The determination of the variation is reiterated for a series of images sequences acquired using calibration devices resulting in first images of mean gray levels different from one sequence to another. Each image of an image sequence of the object under observation is corrected, comprising zones of observation having different gray levels by subtracting from the current image the variation of one gray level relative to the first image of the object, the subtraction being a function of the gray level considered from each zone of observation.

Claims

1. A method for correcting an image of an object under observation, comprising:

obtaining a first sequence of images of a calibration device utilizing an apparatus;

determining a first mean gray level in a zone of interest in a first image in the first sequence of images;

determining a second mean gray level in a zone of interest in a second image in the first sequence of images;

determining a variation value corresponding to a variation between the first mean gray level and the second mean gray level;

obtaining a second sequence of images of the object utilizing the apparatus;

determining a third mean gray level in a zone of interest in a third image in the second sequence of images; and

correcting a fourth image of the object in the second sequence of images based on the variation value and the third mean gray level to obtain a corrected fourth image of the object.

2. The method of claim 1, wherein correcting the fourth image of the object in the second sequence of images based on the variation value and the third mean gray level to obtain the corrected fourth image of the object comprises:

multiplying the variation value and the third mean gray level to obtain a first value; and

subtracting the first value from the fourth image to obtain the corrected fourth image.

3. The method of claim 1, wherein correcting the fourth image of the object in the second sequence of images based on the variation value and the third mean gray level to obtain the corrected fourth image of the object comprises:

multiplying the variation value and the third mean gray level to obtain a first value;

multiplying the first value and a spatial gain factor to obtain a second value; and

subtracting the second value from the fourth image to obtain the corrected fourth image.

4. The method of claim 1, wherein the calibration device is placed in a field of acquisition of the apparatus.

5. The method of claim 1, wherein the calibration device comprises at least first and second zones of interest having first and second mean gray levels, respectively.

6. An apparatus for correcting an image of an object under observation, comprising:

an x-ray detector obtaining a first sequence of images of a calibration device;

a processor configured to determine a first mean gray level in a zone of interest in a first image in the first sequence of images;

the processor further configured to determine a second mean gray level in a zone of interest in a second image in the first sequence of images;

the processor further configured to determine a variation value corresponding to a variation between the first mean gray level and the second mean gray level;

the processor further configured to obtain a second sequence of images of the object;

the processor further configured to determine a third mean gray level in a zone of interest in a third image in the second sequence of images; and

the processor further configured to correct a fourth image of the object in the second sequence of images based on the variation value and the third mean gray level to obtain a corrected fourth image of the object.

7. The apparatus of claim 6, wherein the processor is further configured to multiply the variation value and the third mean gray level to obtain a first value, the processor further configured to subtract the first value from the fourth image to obtain the corrected fourth image.

8. The apparatus of claim 6, wherein the processor is further configured to multiply the variation value and the third mean gray level to obtain a first value, the processor further configured to multiply the first value and a spatial gain factor to obtain a second value, the processor further configured to subtract the second value from the fourth image to obtain the corrected fourth image.

9. The apparatus of claim 6, wherein the calibration device is placed in a field of acquisition of the x-ray detector.

10. The apparatus of claim 6, wherein the calibration device comprises at least first and second zones of interest having first and second mean gray levels, respectively.