Understanding the

relative sharpness

of various video formats.

DV quality is the maximum resolution possible on standard definition television, and most standard TV monitors display quality somewhere between VHS and DVD resolution, even though they are all theoretically the 480i standard (480 interlaced scan lines visible of 525 total).

FRAMES PER SECOND

There are 30 individual video images displayed per second (vs. 24 individual film images per second), giving the illusion of smooth movement. “Interlaced” video actually shows 60 separate images per second, but each is half-resolution with every-other-line scanned on the TV screen, and then the rest filled in. Half of the image is actually photographed a 60^th of a second later in time even though they are displayed on the screen at once. This can create “motion artifacts” that give the effect of a comb along edges of moving objects. “Progressive” video scans the entire 480, 720, or 1080 lines from top to bottom before going to the next image, resulting in a sharper picture. Camcorders that shoot “30p” progressive video often still record in the 60i interlaced format but simply record two halves of the same 30^th of a second instant in time, which eliminates the “comb” motion artifacts. Those that record in “24p” to imitate film actually use complicated mathematical formulas to eliminate and repeat certain frames to simulate 24 images per second. This degrades perception of smooth motion, but some people think it looks more like film transferred to video than original video. It is really only practical for people intending to transfer video footage to film or to high-definition video formats capable of being played back at 24 frames per second (such as Digital Cinema Intitative compatible files or Blu-Ray DVDs for use with high-end projectors or monitors). Any movies designed for standard DVDs or broadcast television in North America should be shot at 30p (or 60i) for smoothest motion. For Europe and many other world locations, 25p or 50i is the standard, but most Europeans have multi-standard equipment that can convert the American standard video signals, whereas very few Americans have multi-standard equipment that can convert European standards for viewing.

PIXELS OF RESOLUTION

Note that one would expect a 720x480 format to display a picture 3x2 (1.5:1) instead of the TV standard of 4x3 (1.33:1) or the widescreen video standard of 16x9 (1.78:1), but the pixels (short for “picture elements”) are not square. They are electronically changed to rectangles that are either narrower or wider as required for each picture format, and the greater number of pixels give slightly more image information than the older 640x480 format using square pixels.

The HDTV format has six times as much picture information as standard definition video, yet only about one-sixth as much as 35mm film quality (or 4k digital video). Nevertheless, a 1080p television is nearly as sharp as typical digital cinema projectors with its picture being the same height of 1080 pixels and its 1920-pixel width almost as many as the "2k" theatrical standard of 2048. The HDV format uses fewer but wider pixels to achieve the same size 16x9 picture width (1440 pixels wide by 1080 pixels high, although actual camera resolution may be closer to 810 pixels high).

Many digital cinema installations use 2k resolution (approximately 2000 pixels wide regardless of height), which is only a quarter the sharpness of the 4k digital standard and only slightly sharper than HDTV’s 1920 by 1080-pixel image. (With the same 1080-pixel height, the “2k” 2048 pixels allow for the wider 1.85:1 theatrical aspect ratio, utilizing 1998 pixels, rather than the 1920-pixel 1.78:1 or 16x9 format that is standard for widescreen television. The "CinemaScope" ratio of 2.39:1 uses the full 2048-pixel width but only 858 pixels of height.)

Most home computers display a much sharper image than standard definition DV quality (using XGA or SXGA monitors), and a few may have as high a resolution as HDTV or hi-def digital cinema, possibly even higher. (Note that typical streaming or downloadable internet video movies have a resolution a quarter or less than that of VHS, which to save memory space is then highly compressed for even lower quality.)

Understand that video images are displayed in ordered horizontal rows and vertical columns of square (or rectangular) picture elements (pixels) in fixed positions, which are the same for every frame of a moving picture. Film images are captured on microscopic randomly-shaped grains of light-sensitive material spread randomly across the image area, so there is no fixed pattern from frame to frame. This results in film displaying an apparently sharper image with “moving” pictures (still images in rapid succession) than if it shows a single frame, whereas video displays the identical pattern for still images and moving images. Thus, a higher-resolution video image is required to simulate the sharpness of movie film of any given resolution. DVDs and HDV video compress the moving image in time as well as the individual frames, so that only a few (or two in the case of HDV) frames each second actually contain all the picture information, but computer processing and the human brain give the illusion of a continuous, sharp moving image.