Function compute_ssim

example_transcoding/utils.cpp:511–556

Reference: https://ece.uwaterloo.ca/~z70wang/research/ssim/index.html

// Reference: https://ece.uwaterloo.ca/~z70wang/research/ssim/index.html
vec4F compute_ssim(const imagef& a, const imagef& b)
{
	imagef axb, a_sq, b_sq, mu1, mu2, mu1_sq, mu2_sq, mu1_mu2, s1_sq, s2_sq, s12, smap, t1, t2, t3;

	const float C1 = 6.50250f, C2 = 58.52250f;

	pow_image(a, a_sq, vec4F(2));
	pow_image(b, b_sq, vec4F(2));
	mul_image(a, b, axb, vec4F(1.0f));

	gaussian_filter(mu1, a, 11, 1.5f * 1.5f);
	gaussian_filter(mu2, b, 11, 1.5f * 1.5f);

	pow_image(mu1, mu1_sq, vec4F(2));
	pow_image(mu2, mu2_sq, vec4F(2));
	mul_image(mu1, mu2, mu1_mu2, vec4F(1.0f));

	gaussian_filter(s1_sq, a_sq, 11, 1.5f * 1.5f);
	add_weighted_image(s1_sq, vec4F(1), mu1_sq, vec4F(-1), vec4F(0), s1_sq);

	gaussian_filter(s2_sq, b_sq, 11, 1.5f * 1.5f);
	add_weighted_image(s2_sq, vec4F(1), mu2_sq, vec4F(-1), vec4F(0), s2_sq);

	gaussian_filter(s12, axb, 11, 1.5f * 1.5f);
	add_weighted_image(s12, vec4F(1), mu1_mu2, vec4F(-1), vec4F(0), s12);

	scale_image(mu1_mu2, t1, vec4F(2), vec4F(0));
	adds_image(t1, vec4F(C1), t1);

	scale_image(s12, t2, vec4F(2), vec4F(0));
	adds_image(t2, vec4F(C2), t2);

	mul_image(t1, t2, t3, vec4F(1));

	add_image(mu1_sq, mu2_sq, t1);
	adds_image(t1, vec4F(C1), t1);

	add_image(s1_sq, s2_sq, t2);
	adds_image(t2, vec4F(C2), t2);

	mul_image(t1, t2, t1, vec4F(1));

	div_image(t3, t1, smap, vec4F(1));

	return avg_image(smap);
}

vec4F compute_ssim(const image_u8& a, const image_u8& b, bool luma)
{