POV-Ray : Documentation : 1.4.2.4 The image gets distorted when rendering a square image
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1.4.2.3 Rotation behaves very strangely   1.4.2.5 Why are there strange dark pixels or noise on my CSG object?

1.4.2.4 The image gets distorted when rendering a square image

"If I tell POV-Ray to render a square image or otherwise change the aspect ratio, the output image is distorted. What am I doing wrong?"

The problem is that the camera is set to an aspect ratio of 4/3, while the picture you are trying to render has an aspect ratio of 1/1 (or whatever).

You can set the aspect ratio with the 'right' keyword in the camera block. The general way to set the correct aspect ratio for your image dimensions is:

camera
{ right x*ImageWidth/ImageHeight
  (other camera settings...)
}

This keyword can also be used to change the handedness of POV-Ray (see the question about Moray and POV-Ray handedness for more details).

Note: One could think "why does not POV-Ray always set automatically the aspect ratio of the camera according to the resolution of the image?".

There is one thing wrong in this thought: It assumes that pixels are always square (ie. the aspect ratio of the pixels is 1/1). The logic of this behaviour comes clear with an example:

Suppose that you design a scene using a regular 4/3 aspect ratio, as usual (like 320x240, 640x480 and so on). This image is designed to look good when viewing in a 4/3 monitor (as they all are in home computers).

Now you want to render this image for the Windows startup image. The resolution of the Windows startup image is 320x400. This resolution has not an aspect ratio of 4/3 and the pixels are not square (the pixels have an aspect ratio of 1/0.6 instead of 1/1). Now, when you render your image at a resolution of 320x400 with POV-Ray and show it with the monitor set to that resolution (as it is set at windows startup when the startup image is shown), the aspect ratio will be the correct one so the image will have the correct proportions (and it will not be squeezed in any direction).

If you had changed the aspect ratio of the camera to 320/400 (instead of using the default 4/3) you would not only have got a different image (showing parts of the scene not shown in the original or hiding parts visible in the original), but it would have looked sqeezed when shown in the 320x400 screen resolution.

Thus, the camera aspect ratio is the aspect ratio of the final image on screen, when viewed in the final resolution (which might not be a 4/3-resolution). Since the monitor screen has an aspect ratio of 4/3, this is the default for the camera as well.

1.4.2.3 Rotation behaves very strangely   1.4.2.5 Why are there strange dark pixels or noise on my CSG object?


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