Aspect Ratio Converter

Aspect ratio describes frame shape as the quotient of width over height, and it is independent of pixel count: 1280 by 720 and 3840 by 2160 are both 16:9, or 1.7778 in decimal form. Reducing a pixel pair by its greatest common divisor recovers the integer ratio, which is why 1920 by 1080 reduces to 16:9 while 4096 by 1716 does not reduce to small integers and is quoted decimally as 2.39:1. Fitting content into a frame of different shape has exactly three outcomes. Padding preserves the whole image and adds bars, letterboxing above and below when the content is wider than the container and pillarboxing left and right when it is narrower, with each bar equal to half the difference between the fitted and actual dimension. Cropping preserves the container and discards pixels, and stretching preserves both at the cost of geometric distortion. The pixel cost of cropping is often larger than it appears. Recutting 1920 by 1080 to a 1:1 square yields 1080 by 1080 and discards about 44 percent of the pixels; recutting the same frame to 9:16 vertical yields 608 by 1080 and discards about 70 percent, which is why vertical deliverables are usually reframed at capture rather than salvaged in post. Practitioners also distinguish display aspect ratio from pixel aspect ratio, since some legacy formats use non-square pixels. NTSC DV at 720 by 480 carries a pixel aspect ratio near 0.9091 for 4:3 display, and the relation display ratio equals width times pixel ratio divided by height is what editing software must apply to avoid showing such footage stretched.

The 4:3 frame originated with the 35 mm motion picture format that W. K. L. Dickson and Thomas Edison's laboratory established around 1892, using four perforations per frame on 35 mm stock. When optical sound tracks were added in the late 1920s they encroached on the image area, and the Academy of Motion Picture Arts and Sciences standardized the corrected Academy ratio of 1.37:1 in 1932. Television adopted the earlier 4:3 shape, and the two systems remained closely matched until studios sought a point of difference from broadcasting. Twentieth Century Fox introduced CinemaScope in 1953 using anamorphic lenses that squeezed a wide field into the standard frame, initially near 2.55:1, later 2.35:1, and revised to 2.39:1 by SMPTE in 1970. Flat widescreen ratios of 1.85:1 in North America and 1.66:1 in Europe developed in parallel through hard matting. The 16:9 ratio that now dominates was not inherited from cinema but engineered as a compromise. Kerns H. Powers, working with SMPTE study groups on high definition television in the early 1980s, observed that if the common ratios from 1.33:1 to 2.35:1 are drawn with equal area, they all fit within, and all contain, a rectangle of about 1.78:1. That geometric mean became 16:9 and was written into HDTV standards, minimizing the worst-case waste when any legacy format is displayed. The rise of smartphone video since the 2010s has reversed the pressure, making 9:16 vertical delivery a routine parallel requirement.