Blind blocking artifact measurement approaches for digital imagery

1. A system for measuring blocking artifacts in a digital image, the digital image being divided into a plurality of blocks and having luminance components and chrominance components, the system comprising:

at least one memory; and

at least one processor operative to execute at least one computer program out of the at least one memory:

to generate, from one of the luminance and chrominance components of the digital image, image pixel data in an image pixel array corresponding to the digital image, the image pixel array having a plurality of pixel locations for pixel values of the image pixel data;

to calculate gradient image data in a gradient image array from the image pixel data, the gradient image array containing a plurality of gradient values of the gradient image data, each of the plurality of gradient values corresponding to a respective gradient value calculated in a specified direction for a respective pair of adjacent pixel locations in the image pixel array;

to calculate normalized gradient image data in a normalized gradient image array from the plurality of gradient values contained in the gradient image array, the normalized gradient image array containing a plurality of normalized gradient values of the normalized gradient image data;

to generate profile data by accumulating the plurality of normalized gradient values contained in the normalized gradient image array with reference to the specified direction;

to apply a 1-dimensional (1-D) discrete Fourier transform (DFT) to the profile data to generate a plurality of DFT coefficients;

to establish a range of block size values for the plurality of blocks in the specified direction;

for each block size value, to generate an initial measurement of blocking artifacts in the digital image from peak magnitudes of the DFT coefficients, thereby obtaining a plurality of initial blocking artifact measurements;

to designate a maximum one of the plurality of initial blocking artifact measurements as a final measurement of blocking artifacts in the digital image; and

to generate an output indicative of the final measurement of blocking artifacts in the digital image.

2. The system of claim 1 wherein the at least one processor is further operative to execute the at least one computer program out of the at least one memory to calculate the normalized gradient image data based at least in part on a predetermined subjective perceptual quality assessment of blocking artifacts.

3. The system of claim 1 wherein the at least one processor is further operative to execute the at least one computer program out of the at least one memory to generate the final measurement of blocking artifacts in the digital image from the peak magnitudes of the DFT coefficients based at least in part on a predetermined subjective perceptual quality assessment of blocking artifacts.

4. The system of claim 1 wherein the at least one processor is further operative to execute the at least one computer program out of the at least one memory to generate a plurality of measurements of blocking artifacts in the digital image with reference to a plurality of specified directions, and to pool data corresponding to the plurality of measurements of blocking artifacts to generate an overall measurement of blocking artifacts in the digital image.

5. The system of claim 4 wherein the at least one processor is further operative to execute the at least one computer program out of the at least one memory to pool the data corresponding to the plurality of measurements of blocking artifacts to generate the overall measurement of blocking artifacts in the digital image based at least in part on a predetermined subjective perceptual quality assessment of blocking artifacts.

6. The system of claim 1 wherein the specified direction corresponds to one of a vertical direction, a horizontal direction, a main diagonal direction, and a minor diagonal direction.

7. The system of claim 1 wherein the at least one processor is further operative to execute the at least one computer program out of the at least one memory to generate absolute values of the gradient image data to produce a plurality of absolute gradient values, and to calculate the normalized gradient image data by normalizing each absolute gradient value by an average of a specified number of gradient values calculated in the specified direction in a vicinity of the respective gradient value in the gradient image array.

8. The system of claim 1 wherein the digital image comprises a digital still image conforming to the JPEG standards.

9. The system of claim 1 wherein the digital image comprises a single digital image of an image sequence conforming to the MPEG or ITU-T H.26n standards.

10. A method of measuring blocking artifacts in a digital image, the digital image being divided into a plurality of blocks and having luminance components and chrominance components, the method comprising the steps of:

generating, by a computerized image pixel array generator from one of the luminance and chrominance components of the digital image, image pixel data in an image pixel array corresponding to the digital image, the image pixel array having a plurality of pixel locations for pixel values of the image pixel data;

calculating, by a computerized gradient image array generator from the image pixel data, gradient image data in a gradient image array, the gradient image array containing a plurality of gradient values of the gradient image data, each of the plurality of gradient values corresponding to a respective gradient value calculated in a specified direction for a respective pair of adjacent pixel locations in the image pixel array;

calculating, by a computerized normalized gradient image array generator from the plurality of gradient values contained in the gradient image array, normalized gradient image data in a normalized gradient image array, the normalized gradient image array containing a plurality of normalized gradient values of the normalized gradient image data;

generating, by a computerized profile data generator, profile data by accumulating the plurality of normalized gradient values contained in the normalized gradient image array with reference to the specified direction;

applying, by a computerized 1-dimensional (1-D) discrete Fourier transform (DFT) component, a 1-D DFT to the profile data to generate a plurality of DFT coefficients;

establishing, by a computerized blockiness measurement component, a range of block size values for the plurality of blocks in the specified direction;

generating, for each block size value by the computerized blockiness measurement component, an initial measurement of blocking artifacts in the digital image from peak magnitudes of the DFT coefficients, thereby obtaining a plurality of initial blocking artifact measurements;

designating, by the computerized blockiness measurement component, a maximum one of the plurality of initial blocking artifact measurements as a final measurement of blocking artifacts in the digital image; and

generating, by a computerized blockiness measurement output generator, an output indicative of the final measurement of blocking artifacts in the digital image.

11. The method of claim 10 wherein the calculating of the normalized gradient image data includes calculating the normalized gradient image data based at least in part on a predetermined subjective perceptual quality assessment of blocking artifacts.

12. The method of claim 10 wherein the generating of the measurement of blocking artifacts in the digital image includes generating the measurement of blocking artifacts in the digital image from the peak magnitudes of the DFT coefficients based at least in part on a predetermined subjective perceptual quality assessment of blocking artifacts.

13. The method of claim 10 further including generating, by the computerized blockiness measurement component, a plurality of measurements of blocking artifacts in the digital image with reference to a plurality of specified directions, and pooling, by a computerized blockiness measurement data pooling component, data corresponding to the plurality of measurements of blocking artifacts to generate an overall measurement of blocking artifacts in the digital image.

14. The method of claim 13 wherein the pooling of the data corresponding to the plurality of measurements of blocking artifacts includes pooling, by the computerized blockiness measurement data pooling component, the data corresponding to the plurality of measurements of blocking artifacts to generate the overall measurement of blocking artifacts in the digital image based at least in part on a predetermined subjective perceptual quality assessment of blocking artifacts.

15. The method of claim 10 wherein the specified direction corresponds to one of a vertical direction, a horizontal direction, a main diagonal direction, and a minor diagonal direction.

16. The method of claim 10 further including generating, by a computerized absolute value generating component, absolute values of the gradient image data to produce a plurality of absolute gradient values, wherein the calculating of the normalized gradient image data includes calculating, by the computerized normalized gradient image array generator, the normalized gradient image data by normalizing each absolute gradient value by an average of a specified number of gradient values calculated in the specified direction in a vicinity of the respective gradient value in the gradient image array.

17. The method of claim 10 wherein the digital image comprises a digital still image conforming to the JPEG standards.

18. The method of claim 10 wherein the digital image comprises a single digital image of an image sequence conforming to the MPEG or ITU-T H.26n standards.

19. A system for measuring blocking artifacts in a digital image, the digital image being divided into a plurality of blocks, the digital image having luminance and chrominance components, the system comprising:

at least one memory; and

at least one processor operative to execute at least one computer program out of the at least one memory:

to generate, from at least one of the luminance and chrominance components of the digital image, image pixel data in an image pixel array corresponding to the digital image, the image pixel array having a plurality of pixel locations for pixel values of the image pixel data;

to calculate gradient image data in a gradient image array from the image pixel data, the gradient image array containing a plurality of gradient values of the gradient image data, each of the plurality of gradient values corresponding to a respective gradient value calculated in a specified direction for a respective pair of adjacent pixel locations in the image pixel array;

to calculate normalized gradient image data in a normalized gradient image array from the plurality of gradient values contained in the gradient image array based at least in part on a predetermined subjective perceptual quality assessment of blocking artifacts, the normalized gradient image array containing a plurality of normalized gradient values of the normalized gradient image data;

to generate profile data by accumulating the plurality of normalized gradient values contained in the normalized gradient image array with reference to the specified direction;

to apply a 1-dimensional (1-D) discrete Fourier transform (DFT) to the profile data to generate a plurality of DFT coefficients;

to establish a range of block size values for the plurality of blocks in the specified direction;

for each block size value, to generate an initial measurement of blocking artifacts in the digital image from peak magnitudes of the DFT coefficients based at least in part on the predetermined subjective perceptual quality assessment of blocking artifacts, thereby obtaining a plurality of initial blocking artifact measurements;

to designate a maximum one of the plurality of initial blocking artifact measurements as a final measurement of blocking artifacts in the digital image; and

to generate an output indicative of the final measurement of blocking artifacts in the digital image.