Image Compositing

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Image Compositing

• ????? ???????
• 2001.1.17
• ??? ? ? ?

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CONTENT

• 1. Image Compositing and Examples
• 2. Blue Screen Mattes
• 3. Alpha Channel
• 4. Porter Duff compositing algebra

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Applications.

• Cel Animation
• ??? ???? ???? ???? ??.
• ???? ??? ???? ?? gt ??? ?????.
• ?? ??? ? ?? gt ???? ?????
  
• gt ?????? ???? ?.
• EX. ??? ?????
• ??? ?? ??? ???? ?? ???? ??.
• 2D ????

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Applications.

• Cel Animation(Cond)

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Application.

• Chroma-keying.
• ??
• ??? ???? ??.
• ??? ??? ???? ???? ??? ??.
• ????? ????? ??.

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Application.

• Chroma-Keying(Cond)
• Chroma(????) ???? ????.
• ?? ?? gt ??? ??? ??.
• ???? ???? ???? ??.
• ?????? ????? ?????? ??? ??.
• ?? ?? gt Chroma-keying.
• EX. ??????, KBS?????

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Blue Screen Mattes

• ??? ???? ?????? ??.
• ??? ????????.
• ?? ?? ???? ??( Black / White seperation positive
  film)?? ??? ?? ??.
• ?,?? ?? gt ?????
• ?? ?? gt ?? ??

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Alpha Channel

• What is a Alpha Channel?
• Assume pixel is a little Square ? ??(????).
• How transparent?
• Image compositing with alpha value.
• Image object(sprite) gt
• a shaped image with partial transparencies.

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Alpha Channel
Bit? ???? ????
1 2(21) ??
8 256(28) ???
16 65536(216) RGB555
24 1600?(224) RGB888
32 1600?8?? ?? RGBa8888
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Over Operator

• Definition
• The fundamental image compositing operator.
• (PorterDuff)
• Assumtion
• Pixel is a Little Square.
• ? ???? ?? ??.
• Color Channel (R,G,B,a) ?? ??.

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Over Operator

• Non-premultiplied alpha formulation
• Premultiplied alpha formulation
• gt PorterDuff Algebra Closure.
• ??? ????.

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Non-Premultiplied

• Image A
• Color A , Alpha Value a
• Image B
• Color B , Alpha Value b
• Image A Image B( B OVER A)
• C bB (1-b)aA bB aA - baA

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Premultiplied

• ????..Cond
• Image A Image B (B over A)
• A aA , B bB .. Premultiplied
• C bB (1-b)aA bB aA - baA
• B A bA

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