Insertion of binary messages in video pictures
A method and a circuit for marking with a binary code a video sequence compressed by motion calculation, from one picture to another, of macroblocks dividing each picture, the digital pictures being distributed in at least two categories according to whether they are coded integrally or by the motion vectors of the macroblocks with respect to the previous picture or to the previous and next pictures, which includes, at least for the pictures coded by motion vectors, only marking the macroblocks for which the motion vectors are greater than a predetermined threshold.
1. A method for marking with a binary code a video sequence compressed by motion calculation, from one picture to another, of macroblocks that form each picture, the method comprising:
receiving digital pictures of at least two categories, including a first category in which the digital pictures are coded integrally and a second category in which the digital pictures are coded by motion vectors of the macroblocks with respect to the previous picture or to the previous and next pictures; and
marking, for the pictures of the second category coded by motion vectors, only the macroblocks for which the motion vectors are greater than a predetermined threshold.
2. The method of claim 1 , comprising marking all the macroblocks of the pictures of the first category.
3. The method of claim 1 , comprising, for the pictures coded by motion vectors:
calculating the motion vectors of the macroblocks of the current picture,
comparing the absolute value of the motion vectors with a predetermined threshold; and
according to whether the motion vector of a macroblock is or not greater than said threshold, submitting or not the pixels of the macroblock to a marking algorithm.
4. The method of claim 3 , wherein a prediction error of each macroblock is calculated, be it or not submitted to the marking algorithm, prior to a coding by discrete cosine transform.
5. The method of claim 1 , wherein said threshold is selected to correspond to a motion greater than 5 pixels from one picture to the next one.
6. The method of claim 1 , applied to a coding according to an MPEG standard.
7. An MPEG coding circuit, comprising means for implementing the method of claim 1 .
8. A method of marking a video, the method comprising:
receiving video motion information representing a change in position of a first image portion of the video;
determining whether the change in position of the first image portion exceeds a threshold; and
marking the first image portion of the video, if the change in position of the first image portion exceeds the threshold.
9. The method of claim 8 , wherein marking the first image portion of the video comprises marking at least one pixel of the first image portion of the video.
10. The method of claim 8 , wherein, prior to receiving the video motion information, the video has been compressed according to changes in positions of macroblocks of the video sequence to determine the video motion information, and further comprising:
determining, for each of the macroblocks, whether a change in the position of each macroblock exceeds a threshold; and
marking at least one of the macroblocks for which the change in position exceeds the threshold.
11. The method of claim 10 , wherein the video motion information comprises motion vectors for the macroblocks, and further comprising:
comparing an absolute value of the motion vectors with a threshold; and
if the absolute value of the motion vector of a macroblock is greater than the threshold, submitting pixels of the macroblock to a marking algorithm.
12. The method of claim 10 , further comprising:
marking all the macroblocks for which the change in position exceeds the threshold.
13. The method of claim 8 , wherein the threshold is selected to correspond to a change in position of the first image portion of at least 5 pixels from a first picture to a second picture of the video.
14. The method of claim 8 , wherein the video has been compressed according to an MPEG standard to determine the video motion information.
15. A device for marking a video, the device comprising:
a motion estimator that receives video motion information representing a change in position of a first image portion of the video and determines whether the change in position of the first image portion exceeds a threshold; and
a first marking unit that marks the first image portion of the video, if the change in position of the first image portion exceeds the threshold.
16. The device of claim 15 , wherein the first marking unit marks the first image portion of the video by altering at least one pixel of the first image portion of the video.