Film grain simulation method based on pre-computed transform coefficients
View Patent ↗Film grain simulation within a receiver occurs by first obtaining at least one block of pre-computed transformed coefficients. The block of pre-computed transformed coefficients undergoes filtering responsive to a frequency range that characterizes a desired pattern of the film grain. In practice, the frequency range lies within a set of cut frequencies f HL , f VL , f HH and f VH of a filter in two dimensions that characterizes a desired film grain pattern. Thereafter, the filtered set of coefficients undergoes an inverse transform to yield the film grain pattern.
1. A method for simulating film grain in a decoded video stream, comprising:
(a) obtaining a pre-computed block of transformed coefficients;
(b) frequency filtering the transformed coefficients responsive to a frequency range that characterize a desired pattern of film grain;
(c) performing an inverse transform on the frequency-filtered transformed coefficients; and
(d) combining a block of film grain obtained by inverse transformation of the frequency-filtered transformed coefficients with the decoded video stream.
2. The method according to claim 1 wherein the step of obtaining the pre-computed block of transformed coefficients further comprises the step of reading at least one pre-computed block of transformed coefficients from a memory.
3. The method according to claim 1 wherein the step of frequency filtering further comprises the step of filtering the transformed coefficients according to a set of cut frequencies f HL , f VL , f HH and f VH of a two-dimensional filter that characterizes the desired film grain pattern.
4. The method according to claim 1 wherein the step of performing an inverse transform coefficients further comprises the step of performing an inverse discrete cosine transform.
5. The method according to claim 1 further comprising the step of scaling the inversely transformed block of coefficients.
6. The method according to claim 1 wherein steps (b) and (c) are repeated for all possible film grain sizes and shapes to obtain a plurality of film grain patterns all derived from one pre-computed block of transformed coefficients.
7. The method according to claim 1 wherein steps (a), (b), and (c) are repeated for all possible film grain sizes and shapes to obtain a plurality of film grain patterns, each derived from a separate pre-computed block of transformed coefficients.
8. The method according to claim 6 further comprising the step of storing each inversely transformed set of filtered coefficients in a memory upon each repeated execution of step (c).
9. The method according to claim 7 further comprising the step of storing each inversely transformed set of filtered coefficients in a memory upon each repeated execution of step (c).
10. The method according to claim 1 further comprising the step of scaling the inversely transformed set of filtered coefficients before the coefficients undergo inverse transformation.
11. Apparatus for simulating film grain in a decoded video stream, comprising:
a first memory for storing at least one a pre-computed block of transformed coefficients;
at least one of a programmed processor, and dedicated logic circuit for simulating film grain in the decoded video stream by (a) obtaining a pre-computed block of transformed coefficients from the memory; (b) frequency filtering the transformed coefficients responsive to a frequency range that characterize a desired pattern of film grain; (c) performing an inverse transform on the frequency-filtered transformed coefficients; and
(d) combining a block of film grain obtained by inverse transformation of the frequency-filtered transformed coefficients with the decoded video stream.
12. The apparatus according to claim 11 wherein the at least one of a programmed processor, and dedicated logic circuit further scales the inversely transformed frequency-filtered transformed coefficients.
13. The apparatus according to claim 11 further comprising a second memory for storing the inversely transformed frequency-filtered transformed coefficients.
14. Apparatus for simulating film grain in a decoded video stream, comprising:
a first memory for storing at least one a pre-computed block of transformed coefficients;
means for obtaining a pre-computed block of transformed coefficients from the memory;
means for frequency filtering the transformed coefficients responsive to a frequency range that characterize a desired pattern of film grain;
means for performing an inverse transform on the frequency-filtered transformed coefficients; and
means for combining a block of film grain obtained by inverse transformation of the frequency-filtered transformed coefficients with the decoded video stream.
15. The apparatus according to claim 14 further comprising means for scaling the inversely transformed frequency-filtered transformed coefficients.
16. The apparatus according to claim 14 further comprising a second memory for storing the inversely transformed frequency-filtered transformed coefficients.