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| -rwxr-xr-x | utils/rkisp1/gen-csc-table.py | 204 |
1 files changed, 204 insertions, 0 deletions
diff --git a/utils/rkisp1/gen-csc-table.py b/utils/rkisp1/gen-csc-table.py new file mode 100755 index 00000000..ca0187ec --- /dev/null +++ b/utils/rkisp1/gen-csc-table.py @@ -0,0 +1,204 @@ +#!/usr/bin/python3 +# SPDX-License-Identifier: GPL-2.0-or-later +# Copyright (C) 2022, Ideas on Board Oy +# +# Generate color space conversion table coefficients with configurable +# fixed-point precision + +import argparse +import enum +import sys + + +encodings = { + 'rec601': [ + [ 0.2990, 0.5870, 0.1140 ], + [ -0.1687, -0.3313, 0.5 ], + [ 0.5, -0.4187, -0.0813 ] + ], + 'rec709': [ + [ 0.2126, 0.7152, 0.0722 ], + [ -0.1146, -0.3854, 0.5 ], + [ 0.5, -0.4542, -0.0458 ] + ], + 'rec2020': [ + [ 0.2627, 0.6780, 0.0593 ], + [ -0.1396, -0.3604, 0.5 ], + [ 0.5, -0.4598, -0.0402 ] + ], + 'smpte240m': [ + [ 0.2122, 0.7013, 0.0865 ], + [ -0.1161, -0.3839, 0.5 ], + [ 0.5, -0.4451, -0.0549 ] + ], +} + + +class Precision(object): + def __init__(self, precision): + if precision[0].upper() != 'Q': + raise RuntimeError(f'Invalid precision `{precision}`') + prec = precision[1:].split('.') + if len(prec) != 2: + raise RuntimeError(f'Invalid precision `{precision}`') + + self.__prec = [int(v) for v in prec] + + @property + def integer(self): + return self.__prec[0] + + @property + def fractional(self): + return self.__prec[1] + + @property + def total(self): + # Add 1 for the sign bit + return self.__prec[0] + self.__prec[1] + 1 + + +class Quantization(enum.Enum): + FULL = 0 + LIMITED = 1 + + +def scale_coeff(coeff, quantization, luma, precision): + """Scale a coefficient to the output range dictated by the quantization and + the precision. + + Parameters + ---------- + coeff : float + The CSC matrix coefficient to scale + quantization : Quantization + The quantization, either FULL or LIMITED + luma : bool + True if the coefficient corresponds to a luma value, False otherwise + precision : int + The desired precision for the scaled coefficient as a number of + fractional bits + """ + + # Assume the input range is 8 bits. The output range is set by the + # quantization and differs between luma and chrome components for limited + # range. + in_range = 255 - 0 + if quantization == Quantization.FULL: + out_range = 255 - 0 + elif luma: + out_range = 235 - 16 + else: + out_range = 240 - 16 + + return coeff * out_range / in_range * (1 << precision) + + +def round_array(values): + """Round a list of signed floating point values to the closest integer while + preserving the (rounded) value of the sum of all elements. + """ + + # Calculate the rounding error as the difference between the rounded sum of + # values and the sum of rounded values. This is by definition an integer + # (positive or negative), which indicates how many values will need to be + # 'flipped' to the opposite rounding. + rounded_values = [round(value) for value in values] + sum_values = round(sum(values)) + sum_error = sum_values - sum(rounded_values) + + if sum_error == 0: + return rounded_values + + # The next step is to distribute the error among the values, in a way that + # will minimize the relative error introduced in individual values. We + # extend the values list with the rounded value and original index for each + # element, and sort by rounding error. Then we modify the elements with the + # highest or lowest error, depending on whether the sum error is negative + # or positive. + + values = [[value, round(value), index] for index, value in enumerate(values)] + values.sort(key=lambda v: v[1] - v[0]) + + # It could also be argued that the key for the sort order should not be the + # absolute rouding error but the relative error, as the impact of identical + # rounding errors will differ for coefficients with widely different values. + # This is a topic for further research. + # + # values.sort(key=lambda v: (v[1] - v[0]) / abs(v[0])) + + if sum_error > 0: + for i in range(sum_error): + values[i][1] += 1 + else: + for i in range(-sum_error): + values[len(values) - i - 1][1] -= 1 + + # Finally, sort back by index, make sure the total rounding error is now 0, + # and return the rounded values. + values.sort(key=lambda v: v[2]) + values = [value[1] for value in values] + assert(sum(values) == sum_values) + + return values + + +def main(argv): + + # Parse command line arguments. + parser = argparse.ArgumentParser( + description='Generate color space conversion table coefficients with ' + 'configurable fixed-point precision.' + ) + parser.add_argument('--precision', '-p', default='Q1.7', + help='The output fixed point precision in Q notation (sign bit excluded)') + parser.add_argument('--quantization', '-q', choices=['full', 'limited'], + default='limited', help='Quantization range') + parser.add_argument('encoding', choices=encodings.keys(), help='YCbCr encoding') + args = parser.parse_args(argv[1:]) + + try: + precision = Precision(args.precision) + except Exception: + print(f'Invalid precision `{args.precision}`') + return 1 + + encoding = encodings[args.encoding] + quantization = Quantization[args.quantization.upper()] + + # Scale and round the encoding coefficients based on the precision and + # quantization range. + luma = True + scaled_coeffs = [] + for line in encoding: + line = [scale_coeff(coeff, quantization, luma, precision.fractional) for coeff in line] + scaled_coeffs.append(line) + luma = False + + rounded_coeffs = [] + for line in scaled_coeffs: + line = round_array(line) + + # Convert coefficients to the number of bits selected by the precision. + # Negative values will be turned into positive integers using 2's + # complement. + line = [coeff & ((1 << precision.total) - 1) for coeff in line] + rounded_coeffs.append(line) + + # Print the result as C code. + nbits = 1 << (precision.total - 1).bit_length() + nbytes = nbits // 4 + print(f'static const u{nbits} rgb2yuv_{args.encoding}_{quantization.name.lower()}_coeffs[] = {{') + + for line in rounded_coeffs: + line = [f'0x{coeff:0{nbytes}x}' for coeff in line] + + print(f'\t{", ".join(line)},') + + print('};') + + return 0 + + +if __name__ == '__main__': + sys.exit(main(sys.argv)) |