Fake rostrum Camera in Premiere?

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ChrisBitz
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Joined: Jun 8 1999

Can anyone think of a cheap way I can fake a rostrum camera thing in Prem?
I want to pan around in a large format picture...

I thought about using a high resolution picture in the video motion bit, but when ever I put it in, premiere scales it to 720x576...

Any other clever ideas?

pcwells
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Joined: Jun 10 1999

Chris,

The Motion control editor will display what's happening in the 720 x 576 frame - but look at the controls, and you'll see a zoom control that works to zoom out as well as zoom in. Premiere's Rostrum effects with high-quality stills are definitely one of its strengths over some other programs.

Hope this helps,

Pete

Alan Roberts at work
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Joined: May 6 1999

Premiere's very good at this. It keeps your still in the source resolution and scans it with a video resolution window. You can move that window off the still, pan, zoom, rotate, tilt, anything you might want to do.

Beware though, if you zoom much, you'll probably get into problems with interlace and resolution. If the stiull has a lot of vertical high frequncy information (like sharp text, graphics, maps etc) they will twitter madly when you zoom out, so you may need to apply some gentle softening to avoid making it objectionable.

Also beware, Premiere deals only in square pixels, and the still will be in square pixels (probably), but you'll have non-square pixels in your 720x576 video, so you'll have to squeeze the still horizontally by 20% to keep the aspect ratios correct. So, first put your still into Photo Shop, Paint Shop Pro, whatever, and change the image size to reduce it horizontally by 20%, uncheck the "maintain aspect ratio" box first. Save the squeezed image and use this one in your video. The non-squareness of DV will stretch it back out again on-screen.

If you're using EditDV, you don't have to do this because it correctly deals with the non-square pixels, but makes a pig's ear of stills anyway because it insists on resampling them to video size BEFORE doing the pan, tilt, zoom etc.

Hope that helps.

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alan@mugswellvillage.freeserve.co.uk. Delete village for a spam-free diet.

RayL
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Joined: Mar 31 1999

>I want to pan around in a large format picture...<

Use the Image Pan filter.

Ray Liffen

dfj
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Joined: Sep 30 2000

Alan Roberts is perfectly correct in saying that Premiere can do excellent Rostrum Camera effects, but he forgot to mention that you should NOT use Video – Motion. This resizes everything to 720 X 576 and then zooms in – not nice! The correct tool to use is, strangely, a FILTER, called Image Pan. This operates on the full resolution original and gives excellent results, though I have had problems doing a ‘hold’ at the beginning or end of a movement – the picture hops as the movement starts or finishes. The only way I have found around this is to do the ‘held’ section as a separate clip, and it then works perfectly.

I would also argue with Alan about the Rectangular/Square pixel problem. It is certainly one I have encountered and compensate for, but I am not sure where he gets 20% from. 720 X 576 is obviously not 4 X 3 if the pixels are square, it should be 768 X 576. But 720/768 is .9375, or 94%. I use Photoshop to shrink the stills by 94% when importing – and just as important, stretch a still frame by 107% when exporting. (I did post this on the old message board, and it then promptly crashed, so keep your fingers crossed.) HOWEVER, I am not sure that it is always true that Premiere does not compensate for square pixels. I did a number of tests at the time, and seem to remember that it resizes higher resolution images correctly. Unfortunately it also does so rather badly, and can introduce aliasing type artefacts (i.e. jagged edges). But if you put in a 720 X 576 frame, so it doesn’t have to interpolate, then it certainly does stretch the image.

So nowadays, I always shrink the image 94% horizontally and then resize in Photoshop to 720 X 576 before importing. (Obviously if it is not a 4 X 3 image you have to put it on a suitable canvas first) This gives excellent results. As further refinements, I reduce saturation and contrast slightly so that the TV image better matches my computer monitor, and also put a black border around the still to reduce the effects of TV cut off discussed in another strand. This can all be done in a single Photoshop Action, so is completely painless.

P.S. I have now found some notes I made of the tests referred to above. ‘True 4 X 3’ means ‘using square pixels in Photoshop’

1. True 4 X 3 (i.e. size is 16cm. X 12cm. for example) is unstretched whether Aspect Ratio is locked or unlocked. BUT artefacts are noticeable on some pix.

2. 720 X 576 is stretched regardless of locked or unlocked Aspect Ratio.

3. 720 X576 is always stretched, but no artefacts.

4. LZW compressed TIF files are OK

5. If a True 4 X 3 with a height of 576 pixels (i.e 768 X 576) is imported with locked Aspect Ratio, it gets stretched, but is not stretched if AR is UN locked!

6. True 4 X 3 in square pixels is 720 X 540, or 768 X 576

7. To make exported video frames correct aspect ratio in Photoshop, increase width only to 107%.

8. To make frames imported from Photoshop correct aspect ratio in Premiere and without artefacts, reduce width only to 94% and resize to 720 X 576. It does not then matter if Aspect Ratio in Premiere is locked or unlocked

Confusing, innit?

R Hart
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Joined: Feb 8 2001

I seem to get the same results whether I use the "video motion" or the "image pan filter", which is: it appears that Premiere 5.1c first converts the image to 720x480 (DV) before doing any scaling or panning. I have tried starting with 1440x960 or 2880x1920 image with and without locked aspect ratios. I have tried a simple "stationary" pan with 720x480 of the high res image and it definitely looks like about half the resolution. What am I missing? If I crop the image to 720x480 and insert it directly for comparision, the cropped image looks fine. What could I be missing?
Thanks.

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R Hart

R Hart

R Hart
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Joined: Feb 8 2001

I found one thing that works to get rid of the "interlacing artifacts". If you set the rendering options under project settings to "no fields", it seems to do the zooming and panning fine with high resolution still images using "image pan" video filter. If the rendering settings have other field settings, it appears to only use one field or the other for the zooming and panning.

As far as I can tell, I need to use field options for exporting my DV files to my DV500, so I had to create a separate project to create the zooming effects, then import them into my project with standard field options. Perhaps there is an easier way.

R Hart

Alan Roberts at work
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Joined: May 6 1999

Ok guys, my hands are up. I haven't used Premiere since early last year when I junked it in favour of EditDV, so I've forgotten some of it's details. But the principle of keeping the still in its original resolution and moving about within that, is exactly the right approach, provided you don't forget that the original image may contain frequencies that cause alias twittering when zoomed inappropriately. The solution is a spatial filter at the time of resampling to video resolution, filtering later doesn't help.

And one more thing, don't do any quick movements this way. Real rostrum qwork uses a real camera, so motion inetgration happens in the camera. That means you can whizz around the still and the motion looks smooth. Do that in Premiere (or any other editor) and the motion will look "gritty" because there's no camera integration (i.e. it's as though the exposure were shuttered to zero time instead of the field interval).

[This message has been edited by Alan Roberts at work (edited 09 February 2001).]

R Hart
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Joined: Feb 8 2001

Alan,
Excellant point. I appreciate your analogy regarding the shutter time being set to zero. I presume we could calculate an optimal pan rate and/or adaptive spacial filter for smooth integration based on that assumption. I suppose someone has programmed a plugin to do just that?

Out of curiosity, I ran a simple verification test with various pan rates. As expected, a rate of less than one pixel per frame (i.e. 30 pixels/second) produced smooth, artifact-free pans. Any rate faster than that results in movement artifacts. I suppose one could use those numbers to estimate the degree of filtering required based on pan speed.

R Hart

Alan Roberts at work
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Joined: May 6 1999

Yes, exactly right. If the movement is less than or equal to the field rate (not frame rate), i.e. 60 or 50 pixels/second, the motion should look smooth. Faster than that will look gritty. Between field and frame rate, the motion will produce differences bewteen the fields, normal-looking in interlaced signals. Don't take any of this as rulings, just as warnings of what might go wrong, and what to look out for.

R Hart
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Joined: Feb 8 2001

I stand corrected. I was using an image with twice the "project" resolution, so two image pixels equal one "project" or "screen" pixel. So yes, it is one pixel/field. Thanks.

R Hart

Alan Roberts at work
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Joined: May 6 1999

Another correction, to me this time. When dealing with horizontal motion, you can use the pixel/field number because that's the image rate for horizontal resolution. When going vertically, you have to use the pixel/frame number because of interlace. When going diagonally, you're on your own.

I'm prepared to post in great depth on sampling theories if there's any serious requests for it.

[This message has been edited by Alan Roberts at work (edited 12 February 2001).]