Image transparency

For most publications, it isn't important whether parts of an image are transparent, since the background of a page is usually white. There are a few cases, however, where transparency information in an image may be important:

  • If the image is being placed in an area that has a shading or color fill (see the Box Tab), then you would normally want the background to show through the transparent parts of the image.

  • Some images may specify a background color other than white, and you may want to use the transparency information to force the background to match the page.

The rendering of images may be different in preview/print and PDF creation, because of differences in capabilities of the medium. In general, however, TopLeaf will honor transparency specified via the color pallette. That is, when the image may contain a limited number of colors (usually 256) and one of these colors has been selected as the transparent color, then that color will be replaced by the appropriate background color to implement transparency.

When rendering a vector image format (EPS or SVG), transparency is not preserved when the image is converted to a bitmap for display. Vector images rendered via a bitmap will always appear on a white background. However, if vector images are included in scalable form in the PDF, then transparency is preserved. Vector images are always rendered as bitmaps in preview/print, so they will always have a white background.

Transparency implemented using an alpha channel is not honored. A future version of TopLeaf will implement alpha channels in PDF output — contact Turn-Key Systems for more information.