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function rgb = hsi22rgb(hsi) % Extract the individual HSI component images. H = hsi(:, :, 1) * 2 * pi; S = hsi(:, :, 2); I = hsi(:, :, 3); % Implement the conversion equations. R = zeros(size(hsi, 1), size(hsi, 2)); G = zeros(size(hsi, 1), size(hsi, 2)); B = zeros(size(hsi, 1), size(hsi, 2)); % RG sector (0 <= H < 2*pi/3). idx = find( (0 <= H) & (H < 2*pi/3)); B(idx) = I(idx) .* (1 - S(idx)); R(idx) = I(idx) .* (1 + S(idx) .* cos(H(idx)) ./ cos(pi/3 - H(idx))); G(idx) = 3*I(idx) - (R(idx) + B(idx)); % BG sector (2*pi/3 <= H < 4*pi/3). idx = find( (2*pi/3 <= H) & (H < 4*pi/3) ); R(idx) = I(idx) .* (1 - S(idx)); G(idx) = I(idx) .* (1 + S(idx) .* cos(H(idx) - 2*pi/3) ./ cos(pi - H(idx))); B(idx) = 3*I(idx) - (R(idx) + G(idx)); % BR sector. idx = find( (4*pi/3 <= H) & (H <= 2*pi)); G(idx) = I(idx) .* (1 - S(idx)); B(idx) = I(idx) .* (1 + S(idx) .* cos(H(idx) - 4*pi/3) ./ cos(5*pi/3 - H(idx))); R(idx) = 3*I(idx) - (G(idx) + B(idx)); % Combine all three results into an RGB image. Clip to [0, 1] to% compensate for floating-point arithmetic rounding effects. rgb = cat(3, R, G, B); rgb = max(min(rgb, 1), 0);