On aspect ratios.
Pixels
Analoguetelevision scanned the image starting in the upper left hand corner of thescreen. Analogue television did not have pixels but rather a beam of electrons.The quantity of electrons fired from a gun slid between more and less so thespot on the monitor was more of a streak than a dot. Color TV introduced a dotscreen. Subsequently computer screens created a grid of glowing elements. Theseelements are pixels.
Pixelis short for picture element.Although we normally think of these as square spots of light on ourcomputer monitors they can also be thought of as a location. We can determine alocation through a co-ordinate system.So pixel 128, 320 is the pixel 128 units from the left and 320 unitsdown from the top. Of course nothing is this simple.
Pixel Aspect Ratio Calculator. This tool will help you calculate pixel aspect ratios (PAR) of video formats. It also enables you to work out the proper resolution for a still image placed into a non-square pixel timeline. The source resolution is the square pixel resolution (ie. The dimensions of the still image) and the target resolution is.
Pixelnumber order can change with picture format. Some early forms of the TIF formatstart numbering from the lower left. Early graphic display programming alsofollowed a co-ordinate system with 0,0 the world center. The down axis would bea negative number so programmers would number the pixels from up from the lowerleft.
Today,image formats generally places 0,0 in the upper left hand corner of the screen.
What is aspect ratio
Theword “aspect” stems from a Middle English word denoting the action or a way oflooking at something. The aspect ratio of a frame is a means of measuring the cinematicframe. While the film gate can be square or rectangular there are restrictionson the frame proportion.The lensalways projects a circle. The physics of light generally results in a darkeningof the edges of this circle and a loss of focus at the edges. Masking thisprojected circle with a rectangle gives us the familiar cinematic frame. Thefilm image is bounded by the film edges creating hard vertical edges on theleft and right. The “film gauge” limits the horizontal size of the actualnegative. 8mm, 16mm, 35mm, 72mm refer to the width of the film stock.
Thereare very few other limitations on the proportion of the frame. The distributionof film to theatres requires some standardization. In 1932 the Academy ofMotion Picture Arts and Sciences made the Academy Ratio a standard ratio. Itwas common until 1953. A short review of film frame aspect ratios involvesnumerous frame sizes. These are ArriScope, Cinerama, Cinerama 70mm,CinemaScope, CinemaScope 55, Dimension 150, Frearless SuperFilm, Grandeur 70mm,Imax, J-D-C Scope, Magnascope, Matted 1.66:1, matted 1.85:1, Metroscope,Panavision, Realife 70mm, Shawscope, Super 35mm, SuperScope, Super Panavision70mm, Super Technirama 70mm, Techniscope, Technovision, Technirama 35mm,Todd-AO, Todd-AO-35, Ultra Panavision 70mm MGM Camera 65, Vitascope,VistiVision, WarnerScope and Widescreen 1.85:1.Most of these formats are not used anymore. Over the yearsthese choices have narrowed though the European and American standards differ.Film gauges 16mm and 8mm are not included in this list.
The 16:9 format wasproposed by Dr Kerns H. Powers, a member of SMPTE Working Group On HighDefinition Electronic Production. When overlapped with their center pointsaligned, he found that all of those aspect ratio rectangles fit within an outerrectangle with an aspect ratio of 1.78:1 and all of them also covered a smallercommon inner rectangle with the same aspect ratio 1.78:1.[4]The geometricmean of the extreme aspect ratios, 4:3 (1.33:1) and 2.35:1, is also1.77:1 which is coincidentally close to 16:9 (1.78:1).
Thestandard analogue television screen ratio of the 1950’s was 1.33:1. This is the proportion of standard Television. The Aspect Ratio is therelationship between the width and height. A Ratio of 1.33:1 or 4:3means that for every 4 units wide it is 3 units high (4 / 3 = 1.33).Currently there are five common aspectratios. These are 4:3, 3:2, 16:9, 1.85:1, and 2.39:1.
Aphysical restraint of the projection system coupled with the desire for widerrectangles in theatrical release resulted in several anamorphic formats. Thesesystems use an anamorphic lens for the camera as well as projector.The anamorphic lens projects a verticaloval rather than a circle.The negativeis squashed horizontally.Anamorphic projection lens creates a wide oval and produces a widerectangle using the same size negative.
Universal Distribution
TheStandard Digitized Video was the outcome of a search for a digital standard for4:3 analogue video. This format introduced the anamorphic pixel. The ratio ofsquare vertical pixels to horizontal pixels had been set at 640x480 this is a1.33:1 aspect ratio. The advent of digital video cameras produced anotherstandard: Digital Video or DV. The opportunity to increase the horizontalresolution by adding anamorphic pixels created the pixel aspect ratio. Think ofthis number as a multiplier. For the following formula let’s call it PAR.
Xtimes PAR divided by Y equals the Frame Aspect Ratio
Theprofessional DV format is 720 horizontal by 486 vertical with a pixel aspect of0.9 wide to 1 high
Written720 x 486 (.9)
Wecan determine the frame aspect ratio with…
720x 0.9 / 486 = 1.33
note:Since the recording of analogue video produces artifacts in the bottom sixlines of the picture most consumer digitizing techniques will cut the bottomsix lines of video and split the difference.
A computer display is alwayssquare pixel.So anamorphic pixelsare displayed through the interpretation of the display. The width is“dithered” to conform “rectangular” pixels to “square”
Ifwe look at 16:9 (1.78) formats we can apply this technique of finding the frameaspect ratio
NTSCWidescreen 720x 480 (1.21)
NTSCD1 Widescreen872x 486 (1) not often used
HDTV720 1280x 720 (1)
HDV10801440x 1080(1.33)
HDTV10801920x 1080 (1)
Allcomputer monitors have a pixel aspect ration of 1:1 or square.This means that the software must widenor narrow the image when editing.
Note:Flash is a vector based program and thus has no pixels to measure.
Letterboxing
Distributinga 4:3 on a 16:9 or 16:9 on a 4:3 frame aspect ratio requires pillar-boxing andletter-boxing.Letterboxing addsblack pixels to the top and bottom of the frame to adjust for the distributionframe aspect of 4:3. Pillar-boxing adds black to the left and right of thepicture to achieve 16:9.