Aspect ratio (image)
The aspect ratio in the broad sense is the ratio of two numbers separated by a colon. Usually so that the ratio of the width of the rectangle is given to its height. A square has an aspect ratio of 1:1. In the video section is also called the aspect ratio.
The indication of the aspect ratio occurs at screens often as a fraction N: M (eg 16:9), often this fraction is normalized to 1 and rounded if necessary (eg 1.78:1 ).
Photo
With negatives, slides and paper method usually the 3:2 format (negative size: 36 × 24 mm, small format, but also 60 × 90 mm, medium format ) is used. Most digital single-lens reflex cameras ( DSLR) to take in this format, both FX ( full-frame ) and DX and APS -C cameras. Cameras for the Four Thirds standard and most compact digital cameras on the other hand use the format 4:3 - the same format used by most medium format cameras in the format of 6 × 4.5 cm. In the medium-format and large-format photography and the formats 1:1 ( 6 × 6 cm), 1:1.17 (6 × 7 cm), are 1:1.25 (4 × 5 inches and 8 x 10 inches), 1:1.4 (5 x 7 inches), 1:1.27 (11 × 14 inch ) to 1:2.5 (4 x 10 inch ) are common. Special panoramic cameras for roll film offer with the formats of 6 × 17 cm or 6 × 20 cm more formats.
Film
During the development of the film, there were always new image formats, most of which, however, sooner or later went out of fashion. Others were able to prevail to this day. In the cinema the image height ( screen height ) usually remains the same - with the exception of, for example, for the demonstration of 70 - mm film suitable cinemas, covering the " normal case" the lowest part of the screen. The image width varies depending on the film format. Always the first height and the width called behind it - why is the cinema - unlike the video where the width is the absolute position data.
The classic image format of 35 mm film is 4 to 3 aspect ratio, this is also the amateur film application. In the movie it is increasingly common widescreen formats with the ratios 1.66:1 ( 5:3 ) and 1.85:1 ( 13:7 ) a. These ratios are generated by corresponding image window in the film camera or masks in the projector that will be inserted into the beam path. So it is just a small section of each film frame used and this then stretched proportionally. (For more explanation → see under Open Mat)
When CinemaScope process one goes another way. The original ratio of 2.35:1 ( 21:9 ) is using the anamorphic lens by a factor of two distorted brought to the footage. The height of the image is retained. At the screening of the finished film, the image is rectified by a factor 2 Anamorphic again.
In the 1950s and early 1960s experimented with various methods and aspect ratios. A special procedure was VistaVision (1954 ), for which new cameras were needed, the recordings on horizontally guided 35 - mm film. The aspect ratio was 2:1 to vertical current release prints.
Brought 2.35:1 image letterboxed to 4:3. OAR is preserved entire image visible
Brought 1.85:1 image letterboxed to 4:3. If OAR 2.35:1, then missing a part of the image content
Brought widescreen formats by pan & scan on 4:3. The image is severely curtailed
TV and Video
In the analog television ( originally black / white) was 4:3 for decades a common format, just as later both the German PAL and SECAM for the French or the U.S. NTSC color television. From the 1990s, the 16:9 ( 1.78:1 = ) has been increasingly used.
The digital television standards such as DVB and ATSC support in a variety of pixel aspect ratios in the display aspect ratios 16:9 and 4:3 and theoretically 2,21:1 (about 20:9 ), which is not used in practice. When high definition television (HDTV ) aspect ratio 16:9 is common.
For DVD, SVCD and DVB, the images are often stored anamorphic - analogous to the CinemaScope process.
Especially with larger and grade televisions sat down with digitization and the move away from the cathode ray tube (CRT) by the aspect ratio of 16:9. From 2009 on, even broader device came in the ratio 21:9 (7:3 = 2.33:1 ) on the market, which can show movies in the 2.35:1 format without horizontal stripes, with no optimized for source material exists and the most of the content to be with vertical bars or inflated or distorted.
Other formats
- √ 2: 1 - The aspect ratio for the DIN A4 sheet and related DIN size. In a division of the rectangle by halving the longer side in turn creates two rectangles with the same aspect ratio (~ 1,4142:1 )
- Φ: 1 - aspect ratio in the golden section (~ 1,618:1 )
- 5: 3 - Finds beside the still wider than 1.85:1 movie format use (equivalent to 15:9 ). PDAs and similar devices of recent times, usually equipped with network and video capabilities as well as a touch screen, use it in the meantime as well, such as with screen resolutions of 800 × 480
Display aspect ratio
The Display Aspect Ratio ( DAR) are the display aspect ratio of a single image in a digital video. This is based on the aspect ratio of the image to display, not the resolution of the image is displayed.
From the Display Aspect Ratio and Pixel Aspect Ratio ( pixel aspect ratio ) results in displaying the actual aspect ratio.
Pixel aspect ratio
The Pixel Aspect Ratio (PAR ) indicates the pixel aspect ratio, ie the ratio of width to height of a single pixel (pixel ) of the output medium.
On computer screens have pixels by default square (PAR 1:1), the ( analog ) TV screen they are - for historical reasons - rectangular, and indeed in PAL 4:3 exactly 128/117 = about 1.094, ie slightly wider than high.
Conversion
For digitally encoded video following mathematical relationship applies:
The pixels are often stored on the medium, square, ie PAR = 1:1; the present aspect ratio of the image ( DAR) with these square stored pixel is thus identical to the SAR.
DAR is the required aspect ratio ( the monitor or, if not identical, only the file), which will come out at the end, usually corresponding to the display monitors 4:3 or 16:9. PAR is then the ratio by which each pixel has to be stretched ( for PAL) or vertically ( for NTSC ) in the representation horizontally to obtain the required aspect ratio DAR; thus all the pixels are not square in the display. Square and non-square relate here always to the shape of the individual pixels, not to the shape of the picture.
The reason is the historical state of the art of the 1920s and 1930s, in which the analog television was developed, as a result, the analog image points of the television signal and monitors could not be realized perfectly square. Therefore, the non-square resolutions 720 × 576 (PAL, what a ratio 5:4 instead of 4:3 equivalent ) and 720 × 480 ( NTSC) originate; for the compensation is sometimes used in the A / D conversion of the square 768 × 576, wherein the same non-square analog pixel is represented by a plurality of digital pixels square. Since the advent of DVD, however, non-square pixel aspect ratios are also preferably used to increase vertical resolution in widescreen movies without increasing the storage and bandwidth requirements; by anamorphic vertical compression (instead of stretching) stored on the medium in 5:4 pixel ratio to 16:9 is achieved a larger resolution.
The scale on the right DAR takes place in the presentation / decoding in the case of. Now the video decoder can calculate the necessary scaling, either the DAR ( MPEG2) or PAR (MPEG4 ) is stored in the data stream. If this attribute is ignored when decoding, there may be distortions. Frequently from the presentation software (video player ) is also supported overwriting the attribute as it is or not in certain cases already wrong in the data stream.
Original aspect ratio
Original Aspect Ratio ( OAR ) is the original aspect ratio.
With the OAR intends the director to let the audience see his film in its original aspect ratio. When image transfer from film to DVD movie or television film while the aspect ratio is not changed, but remains ( 2.35:1, 1.85:1 or 1.66:1 ) untouched. Since the aspect ratio for television broadcasting in PAL and NTSC is enshrined in 1.33:1 (4:3), at a broadcast of a cinema film with OAR in PAL / NTSC is this "empty" area filled black so that above and below the image black bars arise - the so-called letterbox, by some called derisively " mourning bars". With an anamorphic broadcast the image is subsequently compressed in the correct aspect ratio, with black bars also occur. In contrast, the pan-and- scan method, are cut off at the sides of the parts of the image to fill the entire TV screen height with image.