Scanner noise elimination for scanned films
A method for preparing digital image data from an analog image input by scanning, and reducing visibility of the scanning noise, may include estimating a visibility of scanning noise, and a number of scanning samples needed to reduce scanning noise to below a visible threshold. Related methods include scanning, by an analog-to-digital image scanner, an analog image for multiple iterations, resulting in digital image data for each of the iterations; calculating a noise statistic for individual pixels of digital image data across the iterations; determining true values of individual pixels of the digital image data based on the noise statistic for each of the individual pixels and generating scanner noise reduced digital image data wherein pixels are assigned their respective ones of the true values; and saving the scanner noise reduced digital image data in a computer memory.
1. A method for preparing digital image data from an analog image input, the method comprising:
scanning, by an analog-to-digital image scanner, an analog image for multiple iterations, resulting in digital image data for each of the iterations;
calculating, by at least one processor, a noise statistic for scanner noise of individual pixels of the digital image data across the iterations;
determining, by the at least one processor, true values of individual pixels of the digital image data based on the noise statistic for each of the individual pixels and generating scanner noise reduced digital image data wherein pixels are assigned their respective ones of the true values; and
saving the scanner noise reduced digital image data in a computer memory.
2. The method of claim 1 , wherein calculating the noise statistic comprises calculating at least one of a median or average value.
3. The method of claim 1 , further comprising determining, by the at least one processor whether scanner noise in the scanner noise reduced digital image data is below a specified threshold.
4. The method of claim 3 , further comprising, only if the scanner noise in the scanner noise reduced digital image data is not below the specified threshold, repeating all operations of claim 1 for the analog image using a greater number of iterations than previously used for the same analog image.
5. The method of claim 3 , further comprising, only if the scanner noise in the scanner noise reduced digital image data is not above the specified threshold, indicating the scanner noise reduced digital image data in the computer memory is satisfactory for use.
6. The method of claim 5 , further comprising repeating the operations of claim 1 for a sequence of frames resulting in a sequence of scanner noise reduced digital image data in the memory indicated as satisfactory for use, converting the scanner noise reduced digital image data to a digital video file, and storing the digital video file in a computer memory.
7. The method of claim 1 , further comprising determining a number of the multiple iterations for the scanning.
8. The method of claim 7 , further comprising, by the at least one processor, analyzing a visibility of scanner noise based at least in part on a difference between the statistical measure and the true value of the individual pixels.
9. The method of claim 8 , further comprising calculating a Just Noticeable Difference (JND) measure for the pixel area based on the Barton modulation threshold, the minimum, maximum and average luminance values, and the average noise magnitude.
10. The method of claim 7 , further comprising converting a selected pixel area of the digital image data for each of the iterations to the frequency domain and analyzing pixel luminance in the frequency domain, and determining minimum, maximum, and average luminance for the pixel area.
11. The method of claim 10 , wherein the number of multiple iterations is a function of the JND.
12. An apparatus for preparing digital image data from an analog image input, comprising at least one processor coupled to a memory and to an image scanning device, the memory holding instructions, that when executed by the at least one processor, causes the apparatus to perform:
scanning an analog image for multiple iterations, resulting in digital image data for each of the iterations;
calculating a noise statistic for scanner noise of individual pixels of digital the image data across the iterations;
determining true values of individual pixels of the digital image data based on the noise statistic for each of the individual pixels and generating scanner noise reduced digital image data wherein pixels are assigned their respective ones of the true values; and
saving the scanner noise reduced digital image in a computer memory.
13. The apparatus of claim 12 , wherein the memory holds further instructions for determine whether scanner noise in the scanner noise reduced digital image data is below a visible threshold.
14. The apparatus of claim 13 , wherein the memory holds further instructions for, only if the scanner noise in the scanner noise reduced digital image data is not below the specified threshold, repeating all operations of claim 12 for the analog image using a greater number of iterations than previously used for the same analog image, and, only if the scanner noise in the scanner noise reduced digital image data is not above the specified threshold, indicating the scanner noise reduced digital image data in the computer memory is satisfactory for use.
15. The apparatus of claim 14 , wherein the memory holds further instructions for repeating the operations of claim 12 for a sequence of frames resulting in a sequence of scanner noise reduced digital image data in the memory indicated as satisfactory for use, converting the scanner noise reduced digital image data to a digital video file, and storing the digital video file in a computer memory.
16. The apparatus of claim 12 , wherein the memory holds further instructions for, by the at least one processor, analyzing a visibility of scanner noise based at least in part on a difference between the statistical measure and the true value of the individual pixels.
17. The apparatus of claim 16 , wherein the memory holds further instructions for converting a selected pixel area of the digital image data for each of the iterations to the frequency domain and analyzing pixel luminance in the frequency domain, and determining minimum, maximum, and average luminance for the pixel area, and calculating a Just Noticeable Difference (JND) measure for the pixel area based on the Barton modulation threshold, the minimum, maximum and average luminance values, and the average noise magnitude.
18. A method for remastering a cinematic title, the method comprising:
scanning a test film strip, by an analog-to-digital image scanner, for multiple iterations, resulting in digital image data for each of the iterations;
calculating, by at least one processor, a noise statistic for individual pixels of digital image data across the iterations; and
storing the noise statistic in a computer memory associated with the scanner.
19. The method of claim 18 , further comprising:
scanning a film strip of the cinematic title by the analog-to-digital scanner, resulting in digital image data of the cinematic title;
determining, by the at least one processor, true values of individual pixels of the digital image data based on the noise statistic for each of the individual pixels and generating scanner noise reduced digital image data wherein pixels are assigned their respective ones of the true values; and
saving the scanner noise reduced digital image in a computer memory.
20. The method of claim 18 , further comprising:
selecting a film strip for remastering based on the calculated noise statistic.