Question

how many parts tranpency have.........​

Answer 1

The formula for combining C1 = (R1,G1,B1) and C2 = (R2,G2,B2) into a new color C3, where C2 is overlayed on top of C1 with opacity p is usually ( (1-p)R1 + p*R2, (1-p)*G1 + p*G2, (1-p)*B1 + p*B2 ) . See Wikipedia article on transparency for more information.

Answer 2

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Transparency. The GIF and PNG formats also both support transparency. If you need any level of transparency in your image, you must use either a GIF or a PNG. GIF images (and also PNG) support 1-color transparency.