generate_fir_coeff Namespace Reference

Classes
class	IndexTracker

Functions
	withinStdDev (n)
	withinStdDevRange (a, b)

Variables
int	samples_per_pixel = 4
int	subpxls_per_pixel = 3
list	sample_offsets
int	sample_units_width = 5
int	std_dev_max = 3
int	target_sum = 0x110
list	coeffs = []
list	coeffs_rounded = []
int	current_sample_left = sample_offset - sample_units_width
int	current_std_dev_left = -std_dev_max
bool	done = False
	current_sample_right = math.floor(current_sample_left + 1)
int	current_std_dev_right
	coverage = withinStdDevRange(current_std_dev_left, current_std_dev_right)
int	delta = 0
	coeffs_rounded_sum = sum(coeffs_rounded)
list	coeff_diff
	coeff_pkg
	num_elements_to_force_round = abs(coeffs_rounded_sum - target_sum)
tuple	coeffs_rounded_aligned = ([0] * int(sample_align)) + coeffs_rounded

Detailed Description

Copyright 2013 Google Inc.

Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.

Function Documentation

withinStdDev()

generate_fir_coeff.withinStdDev

(

n

)

Returns the percent of samples within n std deviations of the normal.

Definition at line 16 of file generate_fir_coeff.py.

def withinStdDev(n):
  """Returns the percent of samples within n std deviations of the normal."""
  return math.erf(n / math.sqrt(2))
 
 

withinStdDevRange()

generate_fir_coeff.withinStdDevRange	(		a,
			b
	)

Returns the percent of samples within the std deviation range a, b

Definition at line 21 of file generate_fir_coeff.py.

def withinStdDevRange(a, b):
  """Returns the percent of samples within the std deviation range a, b"""
  if b < a:
    return 0;
 
  if a < 0:
    if b < 0:
      return (withinStdDev(-a) - withinStdDev(-b)) / 2;
    else:
      return (withinStdDev(-a) + withinStdDev(b)) / 2;
  else:
    return (withinStdDev(b) - withinStdDev(a)) / 2;
 
 
# We have some smudged samples which represent the average coverage of a range.
# We have a 'center' which may not line up with those samples.
# From center make a normal where 5 sample widths out is at 3 std deviations.
# The first and last samples may not be fully covered.
 
# This is the sub-sample shift for each set of FIR coefficients
#   (the centers of the lcds in the samples)
# Each subpxl takes up 1/3 of a pixel,
#   so they are centered at x=(i/n+1/2n), or 1/6, 3/6, 5/6 of a pixel.
# Each sample takes up 1/4 of a pixel,
#   so the results fall at (x*4)%1, or 2/3, 0, 1/3 of a sample.

Variable Documentation

coeff_diff

list generate_fir_coeff.coeff_diff

Initial value:

=  [(coeff_rounded - coeff) * delta
                  for coeff, coeff_rounded in zip(coeffs, coeffs_rounded)]

Definition at line 106 of file generate_fir_coeff.py.

coeff_pkg

generate_fir_coeff.coeff_pkg

Definition at line 118 of file generate_fir_coeff.py.

coeffs

list generate_fir_coeff.coeffs = []

Definition at line 67 of file generate_fir_coeff.py.

coeffs_rounded

list generate_fir_coeff.coeffs_rounded = []

Definition at line 68 of file generate_fir_coeff.py.

coeffs_rounded_aligned

tuple generate_fir_coeff.coeffs_rounded_aligned = ([0] * int(sample_align)) + coeffs_rounded

Definition at line 132 of file generate_fir_coeff.py.

coeffs_rounded_sum

generate_fir_coeff.coeffs_rounded_sum = sum(coeffs_rounded)

Definition at line 93 of file generate_fir_coeff.py.

coverage

generate_fir_coeff.coverage = withinStdDevRange(current_std_dev_left, current_std_dev_right)

Definition at line 84 of file generate_fir_coeff.py.

current_sample_left

generate_fir_coeff.current_sample_left = sample_offset - sample_units_width

Definition at line 71 of file generate_fir_coeff.py.

current_sample_right

int generate_fir_coeff.current_sample_right = math.floor(current_sample_left + 1)

Definition at line 76 of file generate_fir_coeff.py.

current_std_dev_left

int generate_fir_coeff.current_std_dev_left = -std_dev_max

Definition at line 72 of file generate_fir_coeff.py.

current_std_dev_right

int generate_fir_coeff.current_std_dev_right

Initial value:

=  current_std_dev_left + (
      (current_sample_right - current_sample_left) / sample_units_width
    ) * std_dev_max

Definition at line 80 of file generate_fir_coeff.py.

delta

int generate_fir_coeff.delta = 0

Definition at line 92 of file generate_fir_coeff.py.

done

bool generate_fir_coeff.done = False

Definition at line 74 of file generate_fir_coeff.py.

num_elements_to_force_round

generate_fir_coeff.num_elements_to_force_round = abs(coeffs_rounded_sum - target_sum)

Definition at line 125 of file generate_fir_coeff.py.

sample_offsets

list generate_fir_coeff.sample_offsets

Initial value:

=  [
  math.modf(
    (float(subpxl_index)/subpxls_per_pixel + 1.0/(2.0*subpxls_per_pixel))
    * samples_per_pixel
  ) for subpxl_index in range(subpxls_per_pixel)
]

Definition at line 49 of file generate_fir_coeff.py.

sample_units_width

int generate_fir_coeff.sample_units_width = 5

Definition at line 57 of file generate_fir_coeff.py.

samples_per_pixel

int generate_fir_coeff.samples_per_pixel = 4

Definition at line 46 of file generate_fir_coeff.py.

std_dev_max

int generate_fir_coeff.std_dev_max = 3

Definition at line 60 of file generate_fir_coeff.py.

subpxls_per_pixel

int generate_fir_coeff.subpxls_per_pixel = 3

Definition at line 47 of file generate_fir_coeff.py.

target_sum

int generate_fir_coeff.target_sum = 0x110

Definition at line 64 of file generate_fir_coeff.py.