ReMage image resizer
Aspect ratio (image)
The aspect ratio of an image is its displayed width divided by its height (usually expressed as "x:y" or "x×y," with the joining colon or multiplication symbol articulated as the preposition "by" or sometimes "to").
In video, the two standardized ratios are currently the traditional 4:3 (1.33:1), universal among standard definition video formats, and its modern 16:9 (1.78:1) successor, used in high-definition television and European digital television. Historically, many other aspect ratios no longer in general use have existed in both film and video. Conversion between formats with unequal ratios can be accomplished by either cropping the image to fit the receiving format's ratio or adding black bars (letterboxing or pillarboxing) to retain the original format's ratio. Film ratios tend to be formatted to end with ":1", while video ratios usually prefer to be denoted with whole numbers on both sides of the ratio.
The most common still camera aspect ratios are 4:3 and 3:2, though other ratios such as 5:4, 7:5 and the square format 1:1 are also still found.
The evolution of film and TV aspect ratios
Comparison of three common aspect ratios constrained by the screen diagonal size (the black circle). The widest and shortest box (blue, 2.39:1) and the middle box (green, 16:9) are common formats for cinematography. The most square-like box (red, 4:3) is the format used in standard definition television.
Current video standards
The 4:3 ratio for standard television has been in use since television's origins and many computer monitors use the same aspect ratio. 4:3 is the aspect ratio defined by the Academy of Motion Picture Arts and Sciences as a standard after the advent of optical sound-on-film. By having TV match this aspect ratio, films previously photographed on film could be satisfactorily viewed on TV in the early days of the medium (i.e. the '40s and the '50s). When cinema attendance dropped, Hollywood created widescreen aspect ratios (such as the 1.85:1 ratio mentioned earlier) in order to differentiate their industry from the TV.
16:9 (generally named as: "Sixteen-by-Nine") is the international standard format of HDTV as used in Australia, Canada, Japan, South Korea, and the United States, as well as in Europe on HDTV and non-HD widescreen television (EDTV) PALplus. Japan's Hi-Vision originally started with a 5:3 ratio but converted when the international standards group introduced a wider ratio of 5⅓ to 3 (=16:9). The 1.78:1 aspect ratio was the compromise between the 35 mm US and UK widescreen standard (1.85:1) and the 35 mm European widescreen standard (1.66:1). Many digital video cameras have the capability to record in 16:9. Anamorphic DVD transfers store the information vertically stretched in a 4:3 aspect ratio; if the TV can handle an anamorphic image, it will horizontally decompress the signal to 16:9. If not, the DVD player can reduce scan lines and add letterboxing before sending the image to the TV. Wider ratios such as 1.85:1 and 2.40:1 are accommodated within the 16:9 DVD frame by additional black bars within the image itself. The European Union has instituted the 16:9 Action Plan, just to accelerate the development of the advanced television services in 16:9 aspect ratio, both in PAL and also in HDTV. The Community fund for the 16:9 Action Plan amounted to ECU 228 million.
Two aspect ratios compared with images using the same diagonal size.