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#!/usr/bin/env python3
"""
Generate reference FFT image in OpenEXR format, matching the shader's output format.
"""
import numpy as np
import argparse
from PIL import Image
import OpenEXR
import Imath
def main():
parser = argparse.ArgumentParser(description='Generate reference FFT image')
parser.add_argument('input', type=str, help='Input image file')
parser.add_argument('output', type=str, help='Output EXR file')
parser.add_argument('--size', type=int, default=256, help='Size of the FFT (NxN)')
args = parser.parse_args()
# Load input image and convert to luminance
img = Image.open(args.input).convert('RGB')
img = img.resize((args.size, args.size), Image.Resampling.NEAREST)
img_array = np.array(img, dtype=np.float32) / 255.0
luminance = 0.2126 * img_array[:,:,0] + 0.7152 * img_array[:,:,1] + 0.0722 * img_array[:,:,2]
# Unity's UV origin is bottom-left, NumPy/PIL's is top-left; flip vertically to align
luminance = np.flipud(luminance)
# Perform 2D FFT (no fftshift, matching GPU implementation)
fft_result = np.fft.fft2(luminance)
# Pack complex numbers into RGBA matching shader format:
# R: real part, G: imaginary part, B: 0, A: 1
real_part = fft_result.real.astype(np.float32)
imag_part = fft_result.imag.astype(np.float32)
# Unity's output texture also uses bottom-left origin, so flip output too
real_part = np.flipud(real_part)
imag_part = np.flipud(imag_part)
# Create EXR
height, width = args.size, args.size
header = OpenEXR.Header(width, height)
half_chan = Imath.Channel(Imath.PixelType(Imath.PixelType.FLOAT))
header['channels'] = {'R': half_chan, 'G': half_chan, 'B': half_chan, 'A': half_chan}
# Write EXR
out = OpenEXR.OutputFile(args.output, header)
# Create zero and one arrays for B and A channels
zeros = np.zeros((height, width), dtype=np.float32)
ones = np.ones((height, width), dtype=np.float32)
out.writePixels({
'R': real_part.astype(np.float32).tobytes(),
'G': imag_part.astype(np.float32).tobytes(),
'B': zeros.tobytes(),
'A': ones.tobytes()
})
out.close()
print(f"FFT complete. Output saved to {args.output}")
print(f"Real range: [{real_part.min():.1f}, {real_part.max():.1f}]")
print(f"Imag range: [{imag_part.min():.1f}, {imag_part.max():.1f}]")
if __name__ == "__main__":
main()
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