METHOD AND APPARATUS FOR TRANSFORMING A HIGH DYNAMIC RANGE IMAGE INTO A LOW DYNAMIC RANGE IMAGE

• US 20050117799A1
• Filed: 12/01/2003
• Published: 06/02/2005
• Est. Priority Date: 12/01/2003
• Status: Abandoned Application

• Current Assignee: Inventec Appliances Corporation (Inventec Corporation)
• Original Assignee: Inventec Appliances Corporation (Inventec Corporation)
• Inventors: Fuh, Chiou-Shann, Kao, Chao-Yang, Foo, Chik-Yau
• Application Number:
  US10/707,255
• Publication Number:
  US 20050117799A1
• Time in Patent Office: Days
• US Class Current: 382/169
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 5/009 Global, i.e. based on properties of the image as a whole applied in cameras using an electronic image sensor H04N23/80, H04N23/70
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

A method and an apparatus for transforming a high dynamic range image into a low dynamic range image. The method includes converting first luminance values associated with pixels into a plurality of second luminance values, and utilizing a film transfer function for mapping the second luminance values associated with the pixels into a plurality of third luminance values to generate the low dynamic range image. A second luminance range of the second luminance values is smaller than a first luminance range of the first luminance values, and the film transfer function adds no visual artifact to the low dynamic range image.

Claims

1. A method for converting a high dynamic range image into a low dynamic range image, the high dynamic range image having a plurality of pixels, the pixels respectively corresponding to a plurality of first luminance values, the method comprising following steps:

(a) converting the first luminance values associated with the pixels into a plurality of second luminance values, a second luminance range of the second luminance values being smaller than a first luminance range of the first luminance values; and

(b) utilizing a film transfer function for mapping the second luminance values associated with the pixels into a plurality of third luminance values to generate the low dynamic range image, wherein the film transfer function adds no visual artifact to the low dynamic range image.

2. The method of claim 1 further comprising:

(c) performing a histogram equalization to adjust the second luminance values distributed among the pixels.

3. The method of claim 2 wherein step (c) further comprises:

preventing a total number of predetermined pixels corresponding to a second luminance value from being greater than a predetermined limit.

4. The method of claim 1 wherein step (a) is performed by a global gradient compression.

5. An image processing system comprising:

an image generator for generating a high dynamic range image, the high dynamic range image having a plurality of pixels, the pixels respectively corresponding to a plurality of first luminance values; and

an image processing logic for converting the first luminance values associated with the pixels into a plurality of second luminance values and utilizing a film transfer function for mapping the second luminance values associated with the pixels into a plurality of third luminance values without adding visual artifacts to generate a low dynamic range image;

wherein a second luminance range of the second luminance values is smaller than a first luminance range of the first luminance values.

6. The image processing system of claim 5 being a digital camera.

7. The image processing system of claim 5 wherein the image generator is capable of capturing a plurality of images with different exposures for generating the high dynamic range image.

8. The image processing system of claim 5 wherein the image processing logic is capable of performing a histogram equalization to adjust the second luminance values distributed among the pixels.

9. The image processing system of claim 8 wherein the image processing logic is capable of preventing a total number of predetermined pixels corresponding to a second luminance value from being greater than a predetermined limit.

10. The image processing system of claim 5 wherein the image processing logic is capable of performing a global gradient compression to convert the first luminance values into the second luminance values.