Low-complexity film grain simulation technique
View Patent ↗The simulation of film grain in a video image occurs by first creating a block (i.e., a matrix array) of transformed coefficients for a set of cut frequencies f HL , f VL , f HH and f VH associated with a desired grain pattern. (The cut frequencies f HL , f VL , f HH and f VH represent cut-off frequencies, in two dimensions, of a filter that characterizes the desired film grain pattern). The block of transformed coefficients undergoes an inverse transform to yield a bit-accurate film grain sample and the bit accurate sample undergoes scaling to enable blending with a video signal to simulate film grain in the signal.
1. A method executed by a video signal receiving device for simulating film grain, comprising the steps of:
creating, at the video signal receiving device, coefficients responsive to a band pass region associated with a desired film grain pattern, each coefficient having a value at coordinates (x, y) which is a random value for so long as x and y lie in a band pass region defined by the cut frequencies f HL , f VL , f HH and f VH , which represent cut frequencies (in two dimensions) of a filter that characterizes the desired film grain pattern, but are zero otherwise; and
establishing, at the video signal receiving device, an inverse transformation of the created coefficients to yield a film grain sample for blending in a video image.
2. The method according to claim 1 further comprising the step of setting the coefficient at (0,0) to a zero value.
3. The method according to claim 1 wherein each of the random values obtained for so long as x and y lie in the band pass defined by a set of cut frequencies f HL , f VL , f HH and f VH follows a Gaussian random distribution.
4. The method according to claim 1 wherein each of the random values is obtained by accessing an entry from a pre-computed look-up table of random values.
5. The method according to claim 1 further including the step of scaling the film grain sample.
6. A method executed by a video signal receiving device for creating coefficients used to simulate a desired film grain pattern, comprising the steps of:
(a) obtaining, at the video signal receiving device, a value for each coefficient at coordinates (x, y) which is a random value for so long as x and y lie in a band pass region defined by the cut frequencies f HL , f VL , f HH and f VH , which represent cut frequencies (in two dimensions) of a filter that characterizes the desired film grain pattern, but are zero otherwise;
(b) setting, at the video signal receiving device, the value of the coefficient at coordinates (x, y) to the obtained value; and
(c) repeating steps (a) and (b) until a value is set for every coefficient in the block.
7. The method according to claim 6 further comprising the step of setting coefficient at (0,0) to a zero value.
8. The method according to claim 6 wherein each of the random values is obtained by accessing an entry from a pre-computed look-up table of random values.
9. The method according to claim 6 further including the step of establishing an inverse transform on the coefficients.
10. The method according to claim 9 further including the step of scaling the inverse transform of the coefficients to yield a pattern of film grain samples.
11. The method according to claim 10 further comprising the step of initializing a database of film grain patterns using a single block of coefficients to create all possible film grain patterns.
12. The method according to claim 10 further comprising the step of initializing a database of film grain patterns using multiple blocks of coefficients to create all possible film grain patterns.
13. Apparatus for simulating film grain, comprising one of a programmed processor and logic circuit for (1) creating coefficients responsive to a band pass region associated with a desired film grain pattern, each coefficient having a value at coordinates (x, y) which is a random value for so long as x and y lie in a band pass region defined by the cut frequencies f HL , f VL , f HH , and f VH , which represent cut frequencies (in two dimensions) of a filter that characterizes the desired film grain pattern, but are zero otherwise, 2) establishing an inverse transformation for the created coefficients; and(3) scaling the inversely transformed coefficients to create a simulated pattern of film grain for blending in a video image.
14. The apparatus according to claim 13 wherein the one of the programmed processor or logic circuit creates the coefficients by setting the block coefficient at (0,0)to a zero value.
15. The apparatus according to claim 13 wherein the one of the programmed processor or logic circuit obtains each of the random values by accessing an entry from a pre-computed look-up table of random values.
16. Apparatus for simulating film grain, comprising:
means for creating coefficients responsive to a band pass region associated with a desired film grain pattern, each coefficient having a value at coordinates (x, y) which is a random value for so long as x and y lie in a band pass region defined by the cut frequencies f HL , f VL , f HH and f VH , which represent cut frequencies (in two dimensions) of a filter that characterizes the desired film grain pattern, but are zero otherwise;
means for establishing an inverse transformation for the created coefficients; and
means for scaling the inversely transformed coefficients to create a simulated pattern of film grain for blending in a video image.