METHOD AND APPARATUS FOR GENERATING HIGH DYNAMIC RANGE IMAGE

• US 20190318460A1
• Filed: 06/21/2019
• Published: 10/17/2019
• Est. Priority Date: 12/22/2016
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: BOUZARAA, Fahd, URFALIOGLU, Onay, HALFAOUI, Ibrahim
• Granted Patent: US 11,017,509 B2
• Time in Patent Office: Days
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 2207/20221 Image fusion; Image merging
• CPC Class Codes: G06T 2207/20224 Image subtraction
• CPC Class Codes: G06T 5/10 using non-spatial domain filtering
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors

Abstract

A method and an apparatus for generating a High Dynamic Range, HDR, image are proposed. The method comprises obtaining a set of two or more input images, the two or more input images including a reference image and one or more non-reference images; for each of the one or more non-reference images, performing an image analysis which comprises, for each region of a plurality of regions of the non-reference image, assessing whether the region of the non-reference image and a corresponding region of the reference image show the same image content and declaring the region of the non-reference image as valid or as invalid based on the assessment; and generating the HDR image by fusing the reference image and the one or more non-reference images, wherein the fusing comprises, for each of the one or more non-reference images, disregarding the invalid regions of the respective non-reference image.

Claims

1. A method for generating a High Dynamic Range, HDR, image, comprising:

obtaining a set of two or more input images, the two or more input images including a reference image and one or more non-reference images;

for each of the one or more non-reference images, performing an image analysis which comprises, for each region of a plurality of regions of the non-reference image, assessing whether the region of the non-reference image and a corresponding region of the reference image show the same image content and declaring the region of the non-reference image as valid or as invalid based on the assessment; and

generating the HDR image by fusing the reference image and the one or more non-reference images, wherein the fusing comprises, for each of the one or more non-reference images, disregarding the invalid regions of the respective non-reference image;

wherein the image analysis comprises;

generating a difference image of the non-reference image by subtracting the non-reference image from the reference image or vice versa; and

generating a contrast-enhanced difference image by applying a contrast enhancing transformation to the difference image;

wherein the assessing is on the basis of the contrast-enhanced difference image.

2. The method of claim 1, wherein applying the contrast enhancing transformation to the difference image comprises, for each region of a plurality of regions of the difference image, applying a sigmoid function to an intensity value of the region.

3. The method of claim 1, wherein the assessing whether the region of the non-reference image and a corresponding region of the reference image show the same image content comprises:

comparing an intensity value of a corresponding region of the difference image against a threshold.

4. The method of claim 2, further comprising adapting the contrast enhancing transformation according to a characteristic of the reference image and the non-reference image.

5. The method of claim 4, wherein the characteristic includes a color difference between the reference image and the non-reference image.

6. The method of claim 3, wherein the method further includes determining the threshold based on the non-reference image.

7. The method of claim 6, wherein the determining the threshold includes:

generating a histogram of the non-reference image, wherein the histogram includes multiple bins and each of the multiple bins covers a same range of intensity and has a bin center;

calculating a decrease of each bin of the multiple bins, wherein the decrease is a difference between numbers of pixels respectively at centers of two adjacent bins of the multiple bins;

identifying a bin from the multiple bins, wherein decrease of the identified bin is larger than decrease of any non-identified bin of the multiple bins; and

calculating the threshold according to an intensity of a point in the middle of two bin centers of the identified bin and its next bin.

8. The method of claim 1, wherein the image analysis further comprises performing a morphology operation on the invalid regions of the respective non-reference image.

9. The method of claim 8, the morphology operation includes:

counting the invalid pixels inside a first window in the contrast-enhanced image, wherein the first window is centered on an invalid pixel; and

declaring the invalid pixel on which the first window is centered as valid or invalid according to the counted number of invalid pixels inside the first window;

and/or

defining a second window next to an invalid pixel in the contrast-enhanced image; and

declaring every pixel inside the second window as invalid if a central pixel of the second window is an invalid pixel.

10. An apparatus for generating a High Dynamic Range, HDR, image, comprising a processor configured to perform the steps of claim 1.

12. A computer program with program code means for performing the method according to claim 1 if the program is executed on a computer or on a digital signal processor.

13. A computer program product having a computer readable medium with stored program code means for performing the method according to claim 1 if the program is executed on a computer or by a digital signal processor.

11. An apparatus for generating a High Dynamic Range, HDR, image, comprising:

an obtaining unit configured to obtain a set of two or more input images, the two or more input images including a reference image and one or more non-reference images;

an analysis unit configured to perform, for each of the one or more non-reference images, an image analysis which comprises, for each region of a plurality of regions of the non-reference image, assessing whether the region of the non-reference image and a corresponding region of the reference image show the same image content and declaring the region of the non-reference image as valid or as invalid based on the assessment; and

a generating unit configured to generate the HDR image by fusing the reference image and the one or more non-reference images, wherein the fusing comprises, for each of the one or more non-reference images, disregarding the invalid regions of the respective non-reference image;

wherein the analysis unit is configured to perform the image analysis by;

generating a difference image of the non-reference image by subtracting the non-reference image from the reference image or vice versa; and

generating a contrast-enhanced difference image by applying a contrast enhancing transformation to the difference image;

wherein the assessing is on the basis of the contrast-enhanced difference image.