One of the powerful features of the PDF file specification is the support for transparency in the Canvas. When an image is drawn on the page, the image can have an alpha setting which defines how transparent the image is. The value is between 0 and 1 (where 0 is totally invisible and 1 has no transparency). Transparency is often used for special effects like adding a watermark – draw an image with a 0.2 transparency setting or less.
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