pixelUnpack

// dfmt off
Slice!(double[]*, 1) rgb = [
    [1.0, 0.0, 0.0],
    [0.0, 1.0, 0.0],
    [0.0, 0.0, 1.0],
    [0.470588, 0.470588, 0.470588]
].sliced(4);
// dfmt on

auto unpacked = pixelUnpack!3(rgb, 4, 1);
assert(unpacked.shape == [4, 1, 3]);
assert(unpacked[0][0].length == 3);