The example image for blanking from pyroelectro.com seems off to me. The blanking was on all sides of the images, not just two sides. The beam was off before reaching the end of the line, during the retrace, and still partially at the beginning of the line. The same for the retrace back to the top. The vertical blanking at the top of the image was important as things like CC and VITC were encoded there (as well as some other non-standard uses). Essentially, the active picture was window boxed in the blanking. This example image does not represent that well at all