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Still frames are always captured using square pixels?

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Brian Tallant
Still frames are always captured using square pixels?
on Oct 17, 2014 at 3:37:20 am

I've noticed that when I capture a still, Vegas always captures it using square pixels. For instance, with standard definition video (720x480 and a pixel aspect ratio of 0.9091), Vegas produces an image with a resolution of 655x480. Because it's square pixels, the image is almost identical...but not quite. If you insert that picture onto the timeline and use the Solo Track function to compare it against the original video, you'll see that there's a horizontal line of about a pixel in width right at the very top that's missing from the still.

Is there a way around this? Is there a way to capture the image with the original pixel aspect ratio? Photoshop can easily handle any kind of image so there's no need for square pixels.

Can anyone help?


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Brian Tallant
Re: Still frames are always captured using square pixels?
on Oct 17, 2014 at 4:56:54 am

Alright, I believe I have the problem solved.

There are two ways around the issue:

1) Set both the project settings AND the clip property settings to Square Pixel Aspect Ratio (1.0). Then copy or save a snapshot. The image attributes will say 720x480. But, since it is a square pixel aspect ratio, it will look squeezed.

Then, when you have your still image, place it on the timeline and change the project settings and the clip property settings of both the video and the still back to 0.9091 so it looks normal again.

2) This method is much easier...simply copy or save a snapshot as normal, insert it on the timeline, right click on the event, select properties, and make sure "Maintain Aspect Ratio" is not selected. This produces exactly the same result as the above method.

With a normal snapshot you will lose a little information on the top and bottom. However, in both of the above methods I used the Solo Track feature to toggle between the original image and the captured still and found there was nothing missing from the still.


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John Rofrano
Re: Still frames are always captured using square pixels?
on Oct 19, 2014 at 1:29:53 pm

[Brian Tallant] "Is there a way around this? Is there a way to capture the image with the original pixel aspect ratio?"
As you have seen the way around this is to crop or stretch.
[Brian Tallant] "Photoshop can easily handle any kind of image so there's no need for square pixels."
Photoshop can't help you because this is a math problem. 720 x 0.9091 = 654.552. There is no way to represent 0.552 of a pixel so it gets rounded up to 655. Images don't have any concept of pixel aspect ratio so when Photoshop saves the file it must save whole pixels and will save the same 655x480 image that you have now. What Photoshop does is apply a pixel aspect ratio while you are editing so that you see the image correctly but once saved, it can only use square whole pixels (no fractions). Some programs round down and use 644 and other round up and use 655. This is why you might see things not lining up.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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