Pixel aspect ratio
Pixel aspect ratio and English. Pixel Aspect Ratio (PAR ) represent the ratio of the width of a pixel x and its height Y.
The pixel aspect ratio is the ratio of the display of an image DAR ( Display Aspect Ratio ) can be determined (eg, 16:9 ) and the ratio of image resolution SAR (Storage Aspect Ratio) (eg 1440:1080 ). Generally
Occurrence
In liquid crystal displays, the physical pixels of panels are square in shape, ie each pixel (again consisting of three subpixels: red, green and blue ) of such a screen has both in width and in the height of the same length and thus a pixel aspect ratio of 1: 1
In plasma screens, it happens that a device with an image area in 16:9 format despite square pixel has no 16:9 resolution. Since in such cases differs from the horizontal vertical spacing of the individual pixels, so 768 ( 4:3) are quite resolutions of 1024 × 1024 (1:1) or 1024 × possible.
In digital storage of PAL or NTSC according to ITU- R BT 601 non-square pixels are used. A 4:3 picture here corresponds to a resolution of 720 × 576 ( PAL) or 720 × 480 ( NTSC ) pixels, although typically 720 × 576 or 720 × 480 pixel images are stored (left and right is each 9 black pixels replenished). On video DVDs among other formats are 720 × 576 and 704 × 576 allowed ( because of the divisibility by 16). This results in a PAR of 1.0940 for PAL ( 768/702 ) and for NTSC of 0.9117 ( 640/702 ).
Often can be found 1.0667, which is obtained by reference to a width of 720 pixels (ie 768/720 = 16 /15) for the value of PAL. This value is only if all 720x576 pixels are used for the image.
On a DVD Video may also be stored anamorphic. In this case, a 16:9 image is squeezed into a 4:3 image so that PARs arise from 1.4587 ( PAL) or 1.21557 ( NTSC).
Pixel aspect ratio and standards
Depending on the standard used, different pixel aspect ratios are valid: