Chapter 6 Fundamentals of Digital Video Part 2 Basic Terminiology

In this lecture, you will learn: These basic terminology in digital video: frame size frame aspect ratio pixel aspect ratio timecode

Sampling and Quantization of Motion Temporal: sampling rate: how frequent you take a snapshot of the motion frame rate higher sampling rate: higher frame rate higher frame rate  more frames for the same duration  larger file size

Sampling and Quantization of Motion Each snapshot: a frame an image digitized based on the same concepts of sampling and quantization of images

Frame Size Resolution of the frame image Measured in pixel dimensions No ppi setting: Unlike digital images, there is no pixel per inch (ppi) setting for video because video is not intended for print but for on screen display.

Frame Size Examples Frame size NTSC standard definition 720 x 480 pixels high definition HDV format 1280 x 720 pixels 1440 x 1080 pixels PAL 720 x 576 pixels

Frame Aspect Ratio the ratio of a frame's viewing width to height NOT equivalent to ratio of the frame’s pixel width to height.

Frame Aspect Ratio Examples 4:3 16:9 Example: Standard definition NTSC standard format Examples: Standard definition NTSC wide-screen format High definition digital video High definition TV

Ratio Does Not Match Up? Frame size of a NTSC standard definition DV frame: 720 x 480 720 : 480 = 3 : 2 NOT 4 : 3 or 16 : 9 This is because the pixels are not square!

Pixel Shapes Digital images: square pixels Digital video: may not be square pixels

Pixel Aspect Ratio Pixel Aspect Ratio Pixel Shape 1 square < 1 tall Ratio of pixel width : pixel height Pixel Aspect Ratio Pixel Shape 1 square < 1 tall > 1 wide

Pixel Aspect Ration Examples Video Format Pixel Aspect Ratio Standard format of standard definition (e.g. standard format of the non-blu-ray movies DVD) 0.9 Wide-screen format of standard definition (e.g. wide-screen format of the non-blu-ray movies DVD) 1.2 HDV 720p, QuickTime movies 1.0 HDV 1080i and 1080p 1.333

Let's see if the ratios match up

Standard Format Standard Definition Pixel aspect ratio = 0.9 Frame size = 720  480 Frame aspect ratio = 720  0.9 : 480 = 648 : 480  4 : 3

Wide-screen Format Standard Definition Pixel aspect ratio = 1.2 Frame size = 720  480 Frame aspect ratio = 720  1.2 : 480 = 864: 480  16 : 9

HDV 720p Pixel aspect ratio = 1.0 Frame size = 1280  720 Frame aspect ratio = 1280  1.0 : 720 = 1280 : 720 = 16 : 9

HDV 1080i and 1080p Pixel aspect ratio = 1.333 Frame size = 1440  1080 Frame aspect ratio = 1440  1.333 : 1080  1920 : 1080 = 16 : 9

pixel aspect ratio Video image will be distorted if it is displayed on a system with a different pixel aspect ratio.

For a video of pixel aspect ratio of 1 Displayed correctly on a system of pixel aspect ratio of 1 Displayed incorrectly on a system of pixel aspect ratio of 0.9. The image looks stretched vertically.

For a video of pixel aspect ratio of 1 Displayed correctly on a system of pixel aspect ratio of 1 Displayed incorrectly on a system of pixel aspect ratio of 1.2. The image looks stretched horizontally.

For a video of pixel aspect ratio of 0.9 Displayed correctly on a system of pixel aspect ratio of 0.9 Displayed incorrectly on a system of pixel aspect ratio of 1. The image looks slightly stretched horizontally.

For a video of pixel aspect ratio of 0.9 Displayed correctly on a system of pixel aspect ratio of 0.9 Displayed incorrectly on a system of pixel aspect ratio of 1.2. The image looks stretched horizontally.

For a video of pixel aspect ratio of 1.2 Displayed correctly on a system of pixel aspect ratio of 1.2 Displayed incorrectly on a system of pixel aspect ratio of 0.9. The image looks stretched vertically.

For a video of pixel aspect ratio of 1.2 Displayed correctly on a system of pixel aspect ratio of 1.2 Displayed incorrectly on a system of pixel aspect ratio of 1.0. The image looks slightly stretched vertically.

Distortion Pixel Apect Ratios Distortion video frame's = display system's none video frame's < display system's stretched horizontally video frame's > display system's stretched vertically

Counting Time in Digital Video Timecode: to number frames SMPTE (Society of Motion Pictures and Television Engineers) video timecode number frames in hours, minutes, seconds, and frames drop-frame timecode non-drop-frame timecode

Drop-frame Timecode Example: 00:02:51;20 or 00:02:51.20 Video time is 0 hours, 2 minutes, 51 seconds, and 20 frames Use semi-colons (not colons) Preferable for the NTSC system

Drop-frame Timecode Does NOT mean dropping or removing frames from the video NTSC video is 29.97 fps, not exactly 30 fps Drop-frame timecode renumbers frames to make the timecode more accurately represent the video time based on 29.97 fps It’s able to do this by dropping frames. The specific pattern drops the first two frames of every minute except every tenth minute.

Non-Drop-frame Timecode Example: 00:02:51:20 Video time is 0 hours, 2 minutes, 51 seconds, and 20 frames Use colons