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Scanning Photos and Understanding Pixels
In most of the training DVD’s and manuals I’ve read about scanning photos and adding them to timelines of video editing software there are proceedures for resizing the photos at some point to make up for the difference between the square pixels of the scanned photo and the rectangular pixels of 720 x 480 video. However, when I traced a circle onto a piece of paper, scanned it into Photoshop, saved it as a tiff or png file and dragged it to the timelime in Vegas 6, the circle previewed as still perfectly round and not oval shaped. I did not resize or reshape the circle photo in any way. My standard photos have always looked normal as well when I followed this same procedure. It would seem that the difference in pixel shapes somehow is not an issue in Vegas but is in other editing software. Is this true?
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7 Replies
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“It would seem that the difference in pixel shapes somehow is not an issue in Vegas but is in other editing software. Is this true?”
It certainly is true – and that’s one of the truly good things about Vegas. It doesn’t care what PAR (pixel aspect ratio) you throw at it. As long as you “match output aspect”, Vegas automatically compensates. Other NLEs (like the dpsVelocity I also edit on) is very specific about creating graphics in order to conform to the correct PAR.
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“As long as you match output aspect”
Thanks for the confirmation.
The circle in the photo I mentioned above is round regardless of whether I “match output aspect” or not. That function will fill the screen with the photo if it is smaller than the screen but doesn’t affect the actual shape of the photo. -
Both Photoshop and Vegas have settings to automatically correct for the difference in pixel aspect ratio between CCIR 601 TV pixels (.909) and computer pixels (1.0). So, assuming all is set right, your circles stay round on the computer screen and on the TV monitor.
But keep that circle graphic handy. It’s easy to mis-set either one program or the other, and the graphic is a good check to make sure that all is correct.
Regards,
Doug Graham -
Both Photoshop and Vegas have settings to automatically correct for the difference in pixel aspect ratio between CCIR 601 TV pixels (.909) and computer pixels (1.0)
I have to ask… where in Photoshop and Vegas are those settings?
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The pixel aspect ratio issue has been covered a few times, but here’s a synopsis.
1) Graphics programs typically use square pixels
2) Broadcast formats use non-square pixels
If you are creating stills in Photoshop or whatever for use in Vegas, multiply the destination format width (in pixels) x the destination format pixel aspect ratio.
Ntsc= 720×480 pixels, pixel aspect = .9091
720 x .9091 = 654.552 (round it up or down to a whole value, to 655 or 654)
for a still image size of 655 x480.
If you look at the project presets, you’ll see a table of pixel aspects- these will be different for NTSC widescreen, PAL, and PAL widescreen etc. Use these as your multipliers.
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What I’ve been emphasizing is that you don’t have to do any of the multiplying or resizing you just described above. Simply scan your photo into Photoshop, color correct, reduce the image size if desired but constrain proportions and then save it as a png or tiff file. Don’t resize it to 655 x 480. Open in Vegas and use as is. It worked with my circle image.
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Vegas is designed to assume that all still image files have a pixel aspect ratio of 1:1. You don’t really have to do anything to your images.
However, for the image to fill the NTSC frame it should be 654.5 x 480. Or, if you like whole numbers, make it 720×528. Vegas is quite happy with that dimension.
While Vegas is very forgiving, it’s worth spending the time getting your head around the topic.
Rob Mack
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