Spreading or choking a complex bitmap

Using the Properties Editor, you can spread (or overlap) the border of a complex bitmap to an underlying object or substrate. You can also choke, or shrink, the border of a complex bitmap for a color separation. A choke or spread trap permits objects painted below the bitmap to show through along the outline of the painted region.
Where objects are layered in the page, manually spreading or choking a complex bitmap can only affect the appearance of exposed objects under the complex bitmap, and will not affect the appearance or border of any objects drawn on top of the complex bitmap.

1. Select the Ignore Complex or Ignore All option when processing the PDF file to make any complex bitmaps available for manual trapping.
2. Perform one of the following actions:
   
   • In Mac OS, press Control, and click a complex bitmap.
   • In Windows, right-click the complex bitmap.
     
3. Click Select object's spread/choke. If you have more than one complex bitmap already selected, you can click Select spread/choke for selected objects.
   The complex bitmap appears inside a border.
   
4. Click the trap swatch  button to choose the right or left trap direction arrows. These indicate the direction in which the trap will spread or choke.
   Centerline trapping is not supported when trapping the outline, or border, of a complex bitmap.
   The trap swatch shows the trap color.
5. The trap's color separations appear in cells in the trap color column in the color separations table and may contain the following:
   • A - (hyphen) that appears in a color separations cell for a trap means that this ink is not contributing to the trap or that the trap overprints on this ink. The hyphen will appear only when manually spreading or choking a complex bitmap.
   • A #nn.n value appears in a color separations cell for a trap, where <nn.n> is a value between 0 and 100 percent. This is the mask and average tint value contributed by a complex bitmap. When more than one object is painting a separation, such as a normal object plus one or more complex masks, #nn.n is the maximal tint value derived from those objects.
   • An nn.n value appears in a color separations cell for a trap, where <nn.n> is a value between 0 and 100 percent. This is the tint of the separation color.
6. To change the trap's color separations for a trap, double-click a color separation cell and do one of the following:
   
   1. • Type a new tint value nn.n for that color separation, where <nn.n> is a value between 0 and 100 percent.
      • Type - (hyphen) to prevent that color separation from contributing to the trap or to let the trap overprint on this ink. You can only use the hyphen when manually spreading or choking a complex bitmap.
      • Type # (hash) to request a mask and tint derived from a complex bitmap for that separation. An average tint value will be automatically calculated and displayed once you click Apply.
      • Enter #nn.n, where <nn.n> is a value between 0 and 100 percent, to request a mask derived from a complex bitmap for that separation, in the tint you specify.

             The neutral density for the trap changes as you edit its trap separations.

7. Set a Trap Size.
   When you are spreading or choking a complex bitmap, the final trap width depends on the complex bitmap's pixel resolution.
   The trap width that you specify will be automatically mapped to the integer value of the image resolution and displayed once you click Apply. The final trap width will be a minimum of one pixel.
8. Click Apply.
    

The bitmap's trap is a blue that overprints the underlying green to produce a dark blue-green trap.
A choke or spread trap includes a dilated or contracted version of the original raster mask. Only one raster choke or spread trap can be generated around the entire outline of the painted mask and the trap's width is restricted by the resolution of the original bitmap. You can edit the properties of a spread or choke trap but you cannot edit its trap path if one exists.