Derive spot color from softmasks

This Fixup creates new images with a specified spot color derived from existing softmasks. 

It can be used if the original is a PNG with an alpha channel or a PDF with a softmask. Since the alpha channel/softmask controls transparency, it can be used to derive e.g. a white underlay where the amount of white depends on the amount of visible color.

Note: If a PNG file with an alpha channel is used as input, pdfToolbox will convert the PNG file into a PDF with a softmask.

Example: Derive a white underlay from softmasks

The test file is a PNG with an alpha channel. The background is transparent, and some of the objects in the background also have different levels of transparency. With the Fixup "Derive white from softmasks", these transparency levels from the softmask are used to create a white underlay.

  1. Parameters to define the spot color.
  2. An "Apply to" filter can be used to e.g. limit the Fixup to certain pages.
  3. To apply the spot color everywhere except the existing softmask, the checkbox must be activated.
  4. Layer options: If a layer name is specified, the newly derived images will be placed on a layer. Alternatively, Processing Steps metadata can be defined here. The syntax to interpret the layer name as Processing Steps metadata is <Processing Steps Group>:<Processing Steps Type> e.g. “White:”. If no such Processing Steps layer is present, the layer will be created using the spot color name as the layer name.
  5. If the layer name should be interpreted as Processing Steps metadata, the checkbox must be activated.


With the parameters set in the Fixup above, the result looks like this:

  • A new image in the spot color "White underlay" has been added to the PDF file (the image always has OPM=0 > Overprint: true).
  • The white underlay reflects the transparency levels of the softmask: More transparent print content has less ink coverage of the spot color, more opaque print content has more ink coverage of the spot color.
  • The white underlay is placed on a new layer (layer name is the same as the spot color name).
  • The layer has the Processing Step OCG "White" to indicate the application of white backing ink