Visual privacy protection system
A visual privacy system unilaterally blocks rolling shutter cameras by providing a periodically interrupted ambient light source imposing bright and dark bands on the image yet at a frequency imperceptible to human observers in the environment. Communication of the modulation pattern to authorized cameras allows unaffected imaging in these regions by authorized individuals. The system also contemplates operation in a barcoding mode with a light modulation providing embedded barcodes that can be extracted from images taken in the region to indicate that the images were improperly acquired and to block the images in certain applications.
1. A method of barcoding visual images comprising:
(a) displaying a visual image;
(b) modulating a brightness of the entire visual image to impose a barcode in a recording of the visual image taken by a rolling frame shutter camera, the barcode encoding a predetermined data pattern in a series of bands having a different brightness from other portions of the recording, the predetermined data pattern indicating the visual image was recorded without permission; and
(c) extracting the predetermined data pattern from barcode in the recording to identify piracy of the visual image.
2. The method of claim 1 wherein the barcode is a non-obscuring banding in the visual image.
3. The method of claim 1 wherein the barcode provides bands in the image having at least two different widths.
4. The method of claim 3 wherein the barcodes provide at least a first and second spatial frequency and wherein the step of extracting determines a ratio of the first and second frequencies.
5. The method of claim 4 wherein the step of extracting determines the first and second frequencies using a Fourier transform.
6. The method of claim 5 including the step of averaging all columns of the image generally aligned with bands of the barcode and then determining the first and second frequencies from the averaged column data.
7. The method of claim 4 wherein the barcode provides bands in the image having multiple different spatial frequency pairs having a common frequency ratio.
8. The method of claim 1 wherein the predetermined data pattern is varied over time to produce a series of predetermined data patterns in the visual image.
9. The method of claim 8 wherein the series of predetermined data values encode text.