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| whugemann |
| Posted: Oct 27 2004, 03:15 PM |
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Unregistered
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I would like to superpose a video clip with a static picture that establishes a scale. (In fact, the video shows a the fall of a tachometer needle from 80 km/h to 0 km/h and I need a more precise scale than is on the tachometer.)
I extracted the first frame of that video, drew the scale and exported it (without the background) to a JPEG that shows the scale as black lines on white background.
I now would like to superpose the video with this scale and my first attempt is:
clip1=AviSource("C:\Tacho.avi").ConvertToRGB32()
clip2=ImageReader("C:\Scale.jpg",0,0,1,false).ConvertToRGB32().FlipVertical()
Overlay(clip1,clip3,mode="add",opacity=0.5)
The result is unsatisfactory, because the whole video is now lightend by the white background of the picture. How can I set the alpha channel such that white means transparent?
I made some attempts using mask and ColorMask, by did not succeed. |
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| whugemann |
| Posted: Oct 27 2004, 08:51 PM |
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Unregistered
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O.K., with lots of tries, I found out about it myself. The script must be changed to
clip1=AviSource("C:\Tacho.avi").ConvertToRGB32()
clip2=ImageReader("C:\Scale.jpg",0,0,1,false).ConvertToRGB32().FlipVertical()
clip3=clip2.Invert
Overlay(Clip1,Clip2,mask=Clip3)
If you read the description of the Overlay filter carefully, it says about the parameter "mask": "The darker the image is, the more transparent will the overlay image be."
As I drew black on white, I have to invert the image in order to get a reasonable mask! |
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