Image processing apparatus and method, and program

• US 20050254707A1
• Filed: 05/02/2005
• Published: 11/17/2005
• Est. Priority Date: 05/11/2004
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Takahashi, Naoto
• Granted Patent: US 7,702,151 B2
• Time in Patent Office: Days
• US Class Current: 382/169
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

A histogram is generated on the basis of the pixel value of an image. An LUT used for changing the dynamic range of the image is generated on the basis of the histogram value in each pixel value interval of the generated histogram. The dynamic range of the image is changed on the basis of the generated LUT.

Claims

1. An image processing apparatus which changes a dynamic range of an image, comprising:

histogram generation means for generating at least one of a density value histogram and a differential histogram of the image;

LUT generation means for generating an LUT used for changing the dynamic range of the image on the basis of a histogram value in each pixel value interval of the histogram generated by said histogram generation means; and

changing means for changing the dynamic range of the image on the basis of the LUT generated by said LUT generation means.

2. The apparatus according to claim 1, further comprising change amount setting means for setting a change amount of the dynamic range of the image,

wherein said LUT generation means generates the LUT used for changing the dynamic range of the image, with which the dynamic range set by said change amount setting means is obtained, on the basis of the histogram value in each pixel value interval of the histogram generated by said histogram generation means.

3. The apparatus according to claim 1, further comprising

region extracting means for extracting a region of interest in the image, and

change amount setting means for setting a change amount of the dynamic range in the region of interest extracted by said region extracting means,

wherein said histogram generation means generates at least one of the density value histogram and differential histogram in the region of interest extracted by said region extracting means, and

said LUT generation means generates the LUT used for changing the dynamic range of the image, with which the dynamic range set by said change amount setting means is obtained in the region of interest extracted by said region extracting means, on the basis of the histogram value in each pixel value interval of the histogram generated by said histogram generation means.

4. The apparatus according to claim 1, wherein in compressing the dynamic range of the image, said LUT generation means generates the LUT to compress an interval where the histogram value in each pixel value interval is minimum.

5. The apparatus according to claim 4, wherein in compressing the dynamic range of the image, said LUT generation means changes and generates the LUT so as to make an output pixel value difference small sequentially from an interval where the histogram value in each pixel value interval is small until an output dynamic range equals a desired dynamic range.

6. The apparatus according to claim 1, wherein in expanding the dynamic range of the image, said LUT generation means generates the LUT to expand an interval where the histogram value in each pixel value interval is maximum.

7. The apparatus according to claim 6, wherein in expanding the dynamic range of the image, said LUT generation means changes and generates the LUT so as to make an output pixel value difference large sequentially from an interval where the histogram value in each pixel value interval is large until an output dynamic range equals a desired dynamic range.

8. The apparatus according to claim 1, wherein said LUT generation means sets a limit value for a compression ratio and expansion ratio in each pixel value interval and generates the LUT in a range of the limit value.

9. An image processing method of changing a dynamic range of an image, comprising:

a histogram generation step of generating at least one of a density value histogram and a differential histogram of the image;

an LUT generation step of generating an LUT used for changing the dynamic range of the image on the basis of a histogram value in each pixel value interval of the histogram generated in the histogram generation step; and

a changing step of changing the dynamic range of the image on the basis of the LUT generated in the LUT generation step.

10. A program which implements image processing of changing a dynamic range of an image, comprising:

a program code for a histogram generation step of generating at least one of a density value histogram and a differential histogram of the image;

a program code for an LUT generation step of generating an LUT used for changing the dynamic range of the image on the basis of a histogram value in each pixel value interval of the histogram generated in the histogram generation step; and

a program code for a changing step of changing the dynamic range of the image on the basis of the LUT generated in the LUT generation step.