InDesign Prepress: What Are these White Boxes?

A common question via email and on mailing lists

: what are these

white boxes

I see in my PDF

?

There are two “white box” phenomena, both ex

plainable and both are non-fatal in your PDFs

generated from InDesign

CS.

Source InDesign file:

In this source file

, there is a spot colour (PANTONE 285C)

,

text

+

drop shadow

and a Photoshop file with transparency placed over the top.

Using S

eparation Preview (Window>Output Preview>Separation Preview), the page looks

correct

:

Using either File>Print to a Postscript file and Distilling, or File>Export as Adobe PDF using the [Press] settings, and the [High Resolution] Transparency Flattener style, results in an Acrobat 4.0/PDF 1.3 file (ref:)

Once you open the file in Acrobat 5.0 or 6.0, the following appears:

(a) depicts the “white box phenomena 1” and (b) depicts “white box phenomena 2”

(a) White Box 1: Overprint Preview

This is simple to resolve: Turn on Overprint Preview in Acrobat 5.0 or 6.0 (the free Adobe Reader does not show overprint preview)

The result is as follows. The white boxes dissappear. What are they? Firstly, white is not really white. White is infact a command in Postscript to “Knockout”. This knockout removes all colourants (printed elements) from imaging, and what shows through is the paper stock (substrate). The white we are seeing here is in fact a command to “knockout all process colours to permit the spot colour underneath to show” Overprint preview expresses these overprint/knockout commands in the PDF, and we get the result as below. The Separation Preview in Acrobat 6.0 Professional will also show the PDF correctly. Printing separations to a mjaority of devices will result in the correct output.

Some output devices are not smart enough to recognise the special overprint/knockout commands. Devices that only print Process colours, or convert the spot colours to process to proof the output may result in a view as above. This is not a limitation/bug in InDesign, but rather these output devices not respecting Acrobat 4.0/PDF1.3 constructs.

(b) White Box 2: Image/Vector Smoothing

This white box, or in fact white line, is the edge of an atomic region in the Transparency Flattened PDF. To explain this, here is the same PDF displayed using Wireframe; a feature of Enfocus Pitstop Professional:

You can see that this simple InDesign construct is split into multiple elements. The white line/box we are seeing is on the edge of one of these regions. This “breaking up” of seemingly simple InDesign elements is a function of the Transparency Flattener. Acrobat 4.0/PDF1.3 (and Postscript) cannot directly represent the transparency features. The Transparent elements are broken down into simpler atomic regions resulting in a file that will output and separate correctly.

The white lines/boxes are in fact Acrobat anti-aliasing (smoothing) the edges of these boxes. In ‘normal’ PDFs, this smoothing generates a pleasant, well, smooth, graphic elements. In a Flattened high-quality PDF, these lines are intrusive.

There is a major difference when you turn off smoothing (Smooth line art and Smooth image) in Edit>Preferences in Acrobat:

RIPs and other output devices do not smooth in a similar way, so these lines will not appear.

Suggestions for On-screen PDFs

If you are making a PDF for onscreen use, my strong suggestions are:

1. When printing/exporting, use the Ink Manager to “Convert all Spots to Process”. On screen PDFs don’t need many PANTONE colourants
2. Export as Acrobat 5.0/PDF1.4. This will result in a PDF that is not Transparency Flattened, but the PDF should be smaller and faster to display. The Reader 5.0 has been available since 2001, and is widely available. Including for MacOS 9.