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Why would there be a difference in aspect ratio between a rendered image, and the camera perspective in the viewport? My render is getting squashed to fit a different aspect ratio.

Here is a scene with a circle and emission shader.

Camera perspective in the viewport: enter image description here

Render: enter image description here

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  • $\begingroup$ are you using square pixels? $\endgroup$ – cegaton Jan 18 '15 at 20:34
  • $\begingroup$ Not sure.. I was playing around with different camera presets. I guess those muck with more settings than I realized? $\endgroup$ – ajwood Jan 18 '15 at 20:35
  • $\begingroup$ I cn see the circle in the image getting squeezed horizontally so my feeling is that on the rendering settings your aspect ration is not set to X:1, Y:1 $\endgroup$ – cegaton Jan 18 '15 at 20:38
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    $\begingroup$ K, changing it to 1:1 fixes it. I always thought that was a setting for the frame size. It's actually the pixel dimensions then? $\endgroup$ – ajwood Jan 18 '15 at 20:41
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    $\begingroup$ It's the pixel aspect ratio, not the display aspect ratio. So, for example, to create an NTSC DVD (frame size 720x480) to display as a 16:9 image, you need to set the ratio to 32:27 (that would stretch the pixels' width to the same size as 32x720/27 = 853.333 square pixels, and 853.333/480 = 16/9). $\endgroup$ – user7952 Jan 18 '15 at 20:48
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The image has been rendered with an aspect ratio using non square pixels.

enter image description here

enter image description here

The default setting is X=1 Y=1 so that the image is rendered undistorted using square pixels. You only need to alter with this settings if you are using some display that uses non square Pixels, like old TV or are integrating 3D elements into video shot with anamorphic lenses.

Info from the manual:

Unlike regular computer monitors, some screens (typically older TV sets) do not have the square pixels making it it necessary to generate pre-distorted images which will look stretched on a computer but which will display correctly on a TV set. It is important that you use the correct pixel aspect ratio when rendering to prevent re-scaling, resulting in lowered image quality.

for more info see here: http://helpx.adobe.com/premiere-pro/using/aspect-ratios.html

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