Baffling problem with aspect ratio...(solution found!)

I really don’t understand what is going on. If you follow these steps you’ll see what I mean!

  • Create a new scene. Delete the cube. Add a simple plane at the origin from top view.
  • Place camera facing straight down at plane with X = 0, Y= 0, Z anything +ve (ie. camera over origin facing down). Set the camera to Orthographic Mode. Set PAL as the render output size in the render settings.
  • Press N for the plane and set X scale to 7.2 and Y scale to 5.76. This is the PAL aspect ratio.

Now notice that despite the plane having PAL aspect ratio, it doesn’t fit nicely in the camera limits which are also set to PAL resolution! You can try scaling the plane proportionally (X and Y locked together) or changing the lens setting of the camera but the ratio remains imperfect!

One of the ratios must be wrong. Either the camera limits are drawn wrong, or the Numeric panel input is wrong/doesn’t work or PAL isn’t 720 x 576 or something! Baffling!

Anyone got any ideas? Is this a bug?

Koba

EDIT: In typical manner I’ve just resolved the problem. Apparently, the AspX and AspY render settings change the ratio of X to Y while keeping the final output at 720 x 576. I used to think that the ratio of X and Y was called the “aspect ratio”. This must have something to do with “square pixels” vs “no square pixels” which I have heard about. I’ll look it up but if someone could explain this to me I would be grateful!

yes, in my video tutorial, i recommend setting the plane to 4:3 aspect ratio. Then the plane will properly texture an image for either NTSC or PAL images.

May I have a link to this video tut?

Thanks,

Koba

Ratio of x to y (number of pixels) is known as Screen Aspect Ratio. AspX to AspY (width by height of a pixel) is known as Pixel Aspect Ratio.

Thanks RamboBaby.

Now you have told me what it is called, I have been able to look it up:

The only question now is whether I can change the pixel aspect ratio of an image? Hopefully, this is possible in ImageMagick or something. I’ll have a look…

Koba

No need for Image Magik, just use the AspX: and AspY: fields on the format tab.

Sorry, I should have been clearer.

What do I do to change the pixel aspect of an image that has been rendered out of Blender? What if I want to batch process the pixel aspect of 100 files in a directory?

I think that one out of Blender, square pixels are assumed so it would come down to the screen aspect ratio which is just changing the resolution.

Koba

You can batch process them in Blender (if they are a still sequence) by selecting all of them with RMB in the sequencer, changing the aspX and aspY dimensions and re-render the sequence with Do Sequence enabled. Other than that you might be able to run an action or script in Photoshop but I can’t say for sure. The Gimp may be able to do it but the help system in it is so freakin lame that I don’t even use the program much.

You can batch process them in Blender (if they are a still sequence) by selecting all of them with RMB in the sequencer, changing the aspX and aspY.

Clever! Still not used to the idea of using Blender as an all round image editor/compositor. Blender IS powerful!

Thanks!

Koba