Watermarking digital images to increase bit depth
Watermark data is converted to watermark coefficients, which may be embedded in an image by converting the image to a frequency domain, embedding the watermark in image coefficients corresponding to medium-frequency components, and converting the modified coefficients to the spatial domain. The watermark data is extracted from the modified image by converting the modified image to a frequency domain, extracting the watermark coefficients from the image coefficients, and determining the watermark data from the watermark coefficients. The watermark data may be truncated image data bits such as truncated least significant data bits. After extraction from the watermark, the truncated image data bits may be combined with data bits representing the original image to increase the bit depth of the image. Watermark data may include audio data portions corresponding to a video frame, reference frames temporally proximate to a video frame, high-frequency content, sensor calibration information, or other image data.
1. A computer-implemented method for compressing an image, the image comprising image data representative of the image, the method comprising:
generating, by a processor apparatus, a watermark comprising a set of watermark coefficients representative of a set of truncated image data bits, the truncated image data bits comprising a set of least significant bits of the image data representative of the image;
generating a transformed image by converting a portion of the image data into a set of image coefficients in a frequency domain;
embedding the generated watermark in the transformed image by modifying a subset of the image coefficients with the set of watermark coefficients to form a modified set of coefficients; and
generating a modified image by converting the modified set of coefficients into a spatial domain, the modified image representative of both the portion of the image data and the generated watermark.
2. The method of claim 1 , representing each pixel of the image data by 10 to 12 bits, and wherein each subset of least significant bits comprises 2 to 4 bits.
3. The method of claim 1 , wherein the generating of the watermark comprises:
determining the set of watermark coefficients, each watermark coefficient determined from a local average of truncated image data bits in a contiguous region of the image.
4. The method of claim 1 , wherein the embedding of the generated watermark in the transformed image by modifying the subset of the image coefficients with the set of watermark coefficients further comprises:
determining the subset of the image coefficients from image coefficients having values less than a threshold value.
5. The method of claim 1 , wherein the embedding of the generated watermark in the transformed image further comprises embedding a plurality of copies of the watermark into the transformed image by modifying a plurality of subsets of the image coefficients with a plurality of versions of the set of watermark coefficients.
6. The method of claim 1 ,
wherein the generating of the transformed image comprises determining the set of image coefficients representative of frequencies of the image data by applying a linear transform to one or more properties of the image data; and
wherein the generating of the modified image comprises converting the modified set of coefficients in the spatial domain by applying an inverse of the linear transform to the modified set of coefficients.
7. The method of claim 1 , wherein the image is obtained from a camera, the method further comprising:
applying a sensor correction to the image before truncating the set of least significant bits from the image data.
8. A system for compressing an image, the image comprising image data representative of the image, the system comprising:
a processor apparatus; and
a non-transitory computer-readable apparatus comprising a medium adapted to store a computer program, the computer program having instructions for execution by the processor apparatus, the instructions being configured to, when executed, cause the processor apparatus to:
generate a watermark comprising a set of watermark coefficients representative of a set of truncated image data bits, the set of truncated image data bits comprising a set of least significant bits of the image data representative of the image;
generate a transformed image by conversion of a portion of the image data into a set of image coefficients in a frequency domain;
embed the generated watermark in the transformed image by modification of a subset of the image coefficients with the set of watermark coefficients to form a modified set of coefficients; and
generate a modified image by conversion of the modified set of coefficients into a spatial domain, the modified image representative of both the portion of the image data and the generated watermark.
9. The system of claim 8 , wherein each pixel of the image data is represented by 10 to 12 bits, and wherein each subset of least significant bits comprises 2 to 4 bits.
10. The system of claim 8 , wherein the generation of the watermark comprises:
a determination of the set of watermark coefficients, each watermark coefficient determined from a local average of truncated image data bits in a contiguous region of the image.
11. The system of claim 8 , wherein the embedding of the generated watermark in the transformed image by modifying the subset of the image coefficients with the set of watermark coefficients comprises:
a determination of the subset of the image coefficients from image coefficients having values less than a threshold value.
12. The system of claim 8 , wherein the embedding of the generated watermark in the transformed image comprises embedding a plurality of copies of the watermark into the transformed image by modification of a plurality of subsets of the image coefficients with a plurality of versions of the set of watermark coefficients.
13. The system of claim 8 ,
wherein the generation of the transformed image comprises a determination of the set of image coefficients representative of frequencies of the image data by application of a linear transform to one or more properties of the image data; and
wherein the generation of the modified image comprises a conversion of the modified set of coefficients in the spatial domain by application of an inverse of the linear transform to the modified set of coefficients.
14. The system of claim 8 , wherein the system includes a camera comprising an image sensor, and wherein the image is obtained from the image sensor, the instructions, when executed, further causes the processor apparatus to:
apply a sensor correction to the image before truncation of the set of least significant bits from the image data.
15. A non-transitory computer-readable apparatus comprising a medium adapted to store a computer program, the computer program having instructions for execution by a processor apparatus, the instructions being configured to, when executed, cause the processor apparatus to:
generate a watermark comprising a set of watermark coefficients representative of a set of truncated image data bits, the truncated image data bits comprising a set of least significant bits of image data representative of an image;
generate a transformed image by conversion of a portion of the image data into a set of image coefficients in a frequency domain;
embed the generated watermark in the transformed image by modification of a subset of the image coefficients with the set of watermark coefficients to form a modified set of coefficients; and
generate a modified image by conversion of the modified set of coefficients into a spatial domain, the modified image representative of both the portion of the image data and the generated watermark.
16. The non-transitory computer-readable apparatus of claim 15 , wherein each pixel of the image data is represented by 10 to 12 bits, and wherein each subset of least significant bits comprises 2 to 4 bits.
17. The non-transitory computer-readable apparatus of claim 15 , wherein the generation of the watermark comprises determination of the set of watermark coefficients, each watermark coefficient determined from a local average of truncated image data bits in a contiguous region of the image.
18. The non-transitory computer-readable apparatus of claim 15 , wherein the embedding of the generated watermark in the transformed image by modifying the subset of the image coefficients with the set of watermark coefficients further comprises a determination of the subset of the image coefficients from image coefficients having values less than a threshold value.
19. The non-transitory computer-readable apparatus of claim 15 , wherein the embedding of the generated watermark in the transformed image further comprises embedding a plurality of copies of the watermark into the transformed image by modification of a plurality of subsets of the image coefficients with a plurality of versions of the set of watermark coefficients.
20. The non-transitory computer-readable apparatus of claim 15 ,
wherein the generation of the transformed image further comprises a determination of the set of image coefficients representative of frequencies of the image data by application of a linear transform to one or more properties of the image data; and
wherein the generation of the modified image comprises a conversion of the modified set of coefficients in the spatial domain by application of an inverse of the linear transform to the modified set of coefficients.
21. The non-transitory computer-readable apparatus of claim 15 , wherein the image is obtained from a camera; and
wherein application of a sensor correction to the image occurs before truncation of the set of least significant bits from the image data.