How to create a semi-transparent object?
Adobe introduced semi-transparent objects in PDF 1.4. Many new RIP’s (including Ghostscript) accept PDF 1.4 directly. So there is no need for the transparency features in PostScript. • Ghostscript supports PDF 1.4 in v. 8.00 and up • Adobe CPSI supports PDF 1.4 in v. 3015 and up Standard PostScript has opaque color model. Newer objects completely obscure the objects underneath but parts of the new object can be excluded from painting by clipping path. On level 3 PostScript a sampled image can be used for clipping another sampled image. On level 2 a similar effect can be achived by painting pattern color through the image mask. Very limited transparency effects can be also achived by overprinting spot colors and pure process colors. PDF 1.4 interpreter in Ghostscript is implemented in extended PostScript language. The extensions are visible to the regular PostScript files and can be used to the same effect. The interface is partly documented in doc/language.htm. Read the source code for
