Procedure and device for detecting fades in a sequence of images

Abstract

In order to detect a fade in a sequence of images, a luminance level is calculated for each of the images of a window (termed a detection window) that is N consecutive images in length, and for the image preceding the detection window. A difference of luminance level between the luminance level of the current image and the luminance level of the image preceding the current image is calculated. This is done for each of the N images of the detection window. The presence of a fade for the detection window is deduced if, for at least k images of the detection window, the difference of luminance level is greater than a predefined threshold, with 2<=k<=N.

1 . A method for detecting a fade in a sequence of images, said method comprising the following steps:
 calculating, for each of the images of a window N consecutive images in length, termed detection window, and for the image preceding said detection window, a luminance level;   calculating, for each of said N images of said detection window, a difference of luminance level between the luminance level of the current image and the luminance level of the image preceding said current image; and   deducing therefrom the presence of a fade for said detection window if, for at least k images of said detection window, said difference of luminance level is greater than a predefined threshold, with 2<=k<=N.   
     
     
         2 . A method according to  claim 1 , wherein the luminance level of an image is equal to the sum of the luminance values of each of said pixels of said image. 
     
     
         3 . A method according to  claim 1 , comprising an additional step for validating the presence of a fade in the detection window if a level of motion associated with said detection window is less than a predetermined threshold. 
     
     
         4 . A method according to  claim 3 , wherein the level of motion associated with an image is equal to the ratio between the temporal activity calculated between said image and the image preceding said image, termed the preceding image, and the spatial activity calculated for said image, the level of motion associated with said detection window being equal to the level of motion associated with the last image of said detection window. 
     
     
         5 . A method according to  claim 4 , wherein said temporal activity between said image and said preceding image is equal to the sum of the absolute values of the pixel-wise differences between the luminance values associated with each pixel of said image and the luminance values associated with each pixel of said preceding image, the spatial activity of said image being equal to the sum of the absolute values of the luminance values associated with each pixel of said image. 
     
     
         6 . A device for detecting fades in a sequence of images, comprising:
 means for calculating, for each of the images of a window N consecutive images in length, termed the detection window, and for the image preceding said detection window, a luminance level;   means for calculating for each of said N images of said detection window, a difference of luminance level between the luminance level of the current image and the luminance level of the image preceding said current image; and   means for deducing the presence of a fade for said detection window if for at least k images of said detection window said difference of luminance level is greater than a predefined threshold, with 2<=k<=N.   
     
     
         7 . A video coding device, comprising coding means and a device for detecting fades according to  claim 6 . 
     
     
         8 . A device for structuring a sequence of images, comprising indexation means and a device for detecting fades according to  claim 6 . 
     
     
         9 . A method according to  claim 1 , wherein said images comprise pixels or image points with each of which is associated at least one luminance value, a luminance level being calculated on the basis of the luminance values associated with each of said pixels of each of said images. 
     
     
         10 . A device according to  claim 6 , said images comprising pixels or image points with each of which is associated at least one luminance value, wherein said means of calculation are configured so as to calculate a luminance level of an image on the basis of the luminance values associated with each of said pixels of each of said image. 
     
     
         11 . A device according to  claim 10 , wherein said means of calculation are configured so as to calculate a luminance level of an image as the sum of the luminance values of each of said pixels of said image. 
     
     
         12 . A device according to  claim 6 , comprising validation means for validating the presence of a fade in the detection window if a level of motion associated with said detection window is less than a predetermined threshold, said device comprising an image level decision module for calculating said level of motion. 
     
     
         13 . A video coding device, comprising coding means and a device for detecting fades according to  claim 12 , wherein the image level decision module for calculating a level a motion is configured to decide the type of image to be encoded among at least intra, predicted, and bidirectional types of image.