Rv and the pixel aspect ratio

Hey all,

so we (the studio I work in) ran into some problems with the pixel aspect ratio of an image.

Say we have two images with a pixel aspect ratio of 2.0 and an alpha channel (here it’s a different one, to make it obvious).


If we over them to compare them directly, the alpha channel would be taken into consideration, resulting in an inaccurate compare.

So lately we switched from over to replace, so that we could compare the rgb channels, without the mask, that was hidden in the alpha. Everything worked like a charm until last week, when we started a project with images that have a par different to 1. Now the images get squished.

But only as long as the wipes are at the edges of the image. Moving them results in a correction of the image that has the changed wipes (left). As a workaround, we could also move the second wipe just slightly and the images would fit perfectly over each other (right):

But doing that every time you want to compare something is somewhat annoying. Also it would have to be just the tiniest bit, because you may want to check the corners. Then also the wipes of the top layer would have to be placed precisely.

Has anyone of you had a similar problem so far and knows what’s causing it?

I figured it would have to do with the wipes. The image seems to be reloaded every time the wipes reach the edge or are moved away from them.

There is a visible change in the images with the difference operation. But here the operation is correct, when the wipes are at their edges, moving them destroys the comparison.

Also, the over operation has a slight quality improvement with the wipes not at the edges. But that is barely noticeable.

Thanks for sharing your knowlegde and thoughts on this (as I think quite intriguing) error.

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