source = range(12)
target = [2, 1, 0, '', 5, 4, 3, '', 8, 7, 6, '', 11, 10, 9, '']
numComponents = 0
numPixels = 0
result = range(len(target))
for i, val in enumerate(source):
    result[i + numPixels] = source[i - (2 * (i % 3)) + 2]
    numComponents += 1
    if numComponents == 3:
        result[i + numPixels + 1] = ''
        numPixels += 1
        numComponents = 0
print source
print target
print result