Appendix 1

Appendix 1: Understanding the NTSC Video Format and Digital Video
Logic would say that there is no reason to record more lines of pixels than lines displayed and, usually
this is true. A frame of 1,080 displayed lines will usually consist of 1,080 rows of pixels.
Pixels in early digital formats were square, just as they are on a computer screen. In an effort to
sharpen standard defi nition (SD) video, a rectangular pixel has become the norm. The 4 × 3 aspect
DV formats use a pixel that is taller than wide, the CCIR 601 format. As there are only 480 lines
displayed in SD NTSC video, there are only 480 lines of pixels used in the image. Formats that use
a square pixel have 640 pixels on each line. The CCIR 601 format allows the number of horizontal
pixels to be 720 or an image size of 720 × 480.
The frames seen in Figures A1.5 and A1.6 are extreme blowups of the frame from “No Fui Yo.”
Figure A1.5 is a frame displayed with a “normal” square pixel. Some digital video formats and all
computers use this aspect ratio.
Figure A1.6 is a frame displayed in the CCIR 601 format used by DV and some other digital video
formats. Notice that the pixel is no longer square, but slightly rectangular, taller than wide. This
allows for an increase in the horizontal resolution.
The highlighted area in Figure A1.7 contains the same four pixels in each example. The highlight
helps show the change in pixel aspect ratio.
This can be a problem when creating graphics and titles on a computer screen. As the pixels of the
computer screen are square, the 720 × 480 image will be displayed wider than it will be when displayed
on the video screen.
Figure A1.5 In this pixel close up of a frame from No Fui Yo by Roland De Middle Puch, it can be
seen that the image is recorded as small pixels. In this case the image is displayed with a “normal”
square pixel. In the video display each horizontal row of pixels will become one horizontal line of video.
Image courtesy of Roland De Middle Puch
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