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Task/Grayscale-image/Phix/grayscale-image.phix

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+function to_gray(sequence image)
+sequence color
+    for i=1 to length(image) do
+        for j=1 to length(image[i]) do
+            -- unpack color triple
+            color = sq_div(sq_and_bits(image[i][j], {#FF0000,#FF00,#FF}),
+                                                    {#010000,#0100,#01})
+            image[i][j] = floor(0.2126*color[1] + 0.7152*color[2] + 0.0722*color[3])*#010101
+        end for
+    end for
+    return image
+end function
+
+sequence img = read_ppm("Lena.ppm")
+    img = to_gray(img)