Perceptual modeling of media signals based on local contrast and directional edges

• US 6,633,654 B2
• Filed: 12/13/2000
• Issued: 10/14/2003
• Est. Priority Date: 06/19/2000
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Bradley, Brett Alan, Reed, Alastair M., Hannigan, Brett T.
• Primary Examiner(s): Patel, Jayanti K.
• Assistant Examiner(s): Tabatabai, Abolfazl
• Application Number:
  US09/737,609
• Publication Number:
  US 20020015508A1
• Time in Patent Office: 1,035 Days
• Field of Search: 382/100, 382/232, 380/54, 380/210, 380/287, 380/252, 348/461, 348/463, 713/176, 713/179
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• CPC Class Codes: H04N 1/3216 using Fourier transforms
• CPC Class Codes: H04N 1/32165 using cosine transforms
• CPC Class Codes: H04N 1/3217 using wavelet transforms
• CPC Class Codes: H04N 1/32187 with selective or adaptive application of the additional information, e.g. in selected frequency coefficients
• CPC Class Codes: H04N 1/32192 according to calculated or estimated visibility of the additional information in the image

Abstract

A perceptual model performs an analysis of a media signal, such as an image or audio signal. The model may be used in media signal processing applications such as digital watermarking and data compression to reduce perceptibility of changes made to code the signal. For image applications, the model computes the sensitivity of an image to changes based upon local image contrast, while taking into account the sensitivity of connected directional edges. By comparing the local image strength of various directionally filtered versions of the image, the model creates a directional control vector. This control vector may be used to reduce changes to an image in text and edge regions, and thus, avoid perceptible artifacts in those regions. The model takes into account the local contrast of the image and the directional control vector to create a gain vector. Using the local contrast measurements, the model follows the eye'"'"'s nonlinear response to contrast discrimination.

Claims

1. A method for perceptual modeling of a media signal comprising:

analyzing the media signal to compute a measure of directional edges in the signal;

based at least in part on the measure of directional edges, computing control data used to selectively suppress a digital watermark signal around the directional edges in a manner that controls perceptibility of the digital watermark signal embedded within the media signal, wherein the control data is used to reduce perceptibility of the watermark embedded in the media signal, and wherein the control data is used to adjust signal strength of an audio watermark.

2. The method of claim 1 wherein the audio watermark is applied in a temporal domain and the control data is used to adjust the signal strength of the audio watermark in the temporal domain.

3. The method of claim 1 wherein the audio watermark is applied in a transform domain and the control data is used to adjust the signal strength of the audio watermark in the transform domain.

4. The method of claim 3 wherein the transform domain is a time-frequency domain.

5. A computer readable medium having software for performing the method of claim 1.

6. A method for perceptual modeling of a media signal comprising:

analyzing the media signal to compute a measure of directional edges in the signal;

based at least in part on the measure of directional edges, computing control data used to selectively suppress a digital watermark signal around the directional edges in a manner that controls perceptibility of the digital watermark signal embedded within the media signal; and

using the control data to control lossy compression of the media signal.

7. A perceptual analyzer of a media signal comprising:

a directional edge analyzer for measuring directional edges at samples in the media signal;

a local contrast analyzer for measuring local contrast at samples in the media signal;

a perceptual model for mapping local contrast to a measure of sensitivity; and

a control data calculator operable to combine data from the directional edge analyzer and the perceptual model to compute control data used to adjust changes to the media signal in a manner that minimizes perceptibility of the changes, wherein at least the data from the directional edge analyzer is used to selectively suppress signal strength of a digital watermark signal around the directional edges.