Understanding blending color spaces

For both Adobe Acrobat and the Assembler service, adding a PageContent, Watermark, Background, PageOverlay, or PageUnderlay to a PDF document may change the appearance of other page content under certain conditions.

If added content (a PageContent, Watermark, Background, PageOverlay, or PageUnderlay) or the target page in the document has opacity of less than 100%, has RGB content, and is added to a page in a document that does not have a blending color space specified on each PDF page, it changes the appearance of other page content.

Those components that have RGB colors in the added content, or in the original document page will be distorted because they are converted to CMYK, which is the default blending color space. Colors within added content are always in the RGB color space, even if all requested colors are black or gray. A color shift will also occur if an explicit CMYK or ICC blending color space is specified, but it is assumed that was intended and no warning is issued.

To prevent this from occurring, either add an RGB or RGB-compatible ICC blending color space to the original document, or set the opacity in the DDX to 100% (1.0). Note that the Assembler service does not provide the capability of setting the blending color space.

Note: To change blending profiles in Acrobat, select Advanced > Print Production > Convert Colors > Page-Level Transparency Blending Space.

For example, the following DDX file adds a watermark with opacity of 25% to the file test.pdf. The text in the resulting file, result.pdf, will be darker in appearance than in the original. This occurs because the /ExtGState is applied to the entire page instead of the watermark itself. Removing the watermark removes the /ExtGState and the text returns to its original lighter color:

Example: Adding a watermark with opacity less than 100%

<?xml version="1.0" encoding="UTF-8"?>

<DDX xmlns="http://ns.adobe.com/DDX/1.0/">

	<PDF result="result.pdf">

		<PDF source="test.pdf"/>

			<Watermark rotation="45" opacity="25%">

				<StyledText><p font-size="72pt">Draft</p></StyledText>

			</Watermark>

	</PDF>

</DDX>