Contents of this post: Click a subject below to advance to that section.

• Thin white lines on my PDF
• Certain letters appear “thicker” than the rest, i.e., an uppercase “i” or a lowercase “L”

 

Thin White lines on my PDF:

These white lines are actually an artifact of the kind of antialiasing that Adobe products use. The technical term is “seam stitching”, and it is the result of a PDF that contains flattened transparency.

The “Pre-PDF” fix:

Avoid exporting to a version of PDF that does not support transparency, i.e., compatibility: Acrobat 4 (PDF 1.3)

The “Post-PDF” fix:

The “pre-PDF fix” may not be an option because you are stuck with a finished PDF, along with client that is freaking out. In that case, instruct your client to do the following:

In Acrobat preferences for Page Display, UNCHECK the option marked Smooth line art in Acrobat Pro or Adobe Reader’s “Page Display” preference.

-or-

In Acrobat preferences for Page Display, UNCHECK the option marked Smooth images in Acrobat Pro or Adobe Reader’s “Page Display” preference.

Sometimes simply zooming in on your PDF is enough to rectify the issue, but not always.

-or-

If the white lines then disappear, you know it’s simply a screen issue due to the antialiasing. If the white lines are still there when this setting is turned off, then the lines will appear when the file prints. Just for the record, I have yet to find a case where the white lines print—but this is a good way to ensure peace of mind (especially for your client). You are then safe to turn the Smooth Line Art setting back on again.

Basically, the Smooth Line Art setting uses an antialiasing method that can cause raster parts of your file to shift a fraction, which may result in uneven pixel boundaries. You can’t keep the setting off because then all of your line art will appear jagged as demonstrated in the examples a bit further down in this post.

 

 

 

 

After:

with “Smooth line art” unchecked

 

You are probably asking yourself, why wouldn’t I always leave this box unchecked? Do not do that. As you can see in the examples below, unchecking this box leads to other on screen issues with line art. It’s most noticeable in the “valpak.com” button in the lower right corner. Notice how it became much more jagged. The key to remember is that the result of turning this setting on or off will not affect the printed file, it is there to improve the way the PDF looks on screen.

 

Before:

with “Smooth line art” checked  (notice the valpak.com button in lower right corner—it looks fine)

 

 

After:

with “Smooth line art” unchecked  (notice the valpak.com button in lower right corner—it looks jagged)

 

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Certain letters appear “thicker” than the rest, i.e., an uppercase “i” or a lowercase “L”.

This issue is not related to transparency flattening, but it also relates to a PDF display anomaly. Most often this occurs with sans serif text, and it is usually a lower case “L”, an uppercase “i”, or a number “1”. Secondly, this will happen with a logo that had its fonts converted to outlines. As a general rule of thumb, you should avoid converting fonts to outlines when your intention is to export a PDF. Once you convert a font to outlines it no longer has a font’s built in “font hinting.” Font hinting (also known as instructing) is the use of mathematical instructions to adjust the display of a font so that it lines up with a rasterized grid. In other words, hinting ensures a font will properly display on screen, even at small sizes such as the example below. Once you convert a font to outlines, hinting is gone and the PDF display may assign some arbitrary antialiasing, making some of the vector objects appear thicker than they should.

Sometimes you have no choice because the logo was provided to you this way. In that case, you can assure yourself that it will print fine by unchecking “Enhance thin lines” in the page display preferences.

In the example below the lowercase “L” in “by planet beach” is noticeably thicker than the other letters. It is clearly visible in the zoomed in screen shot.

 

 

 

Notice the difference after “Enhance thin lines” was unchecked. At this point be confident it will not print with the issue you originally saw.

 

 

So you may be saying to yourself,

“What good is telling me the fix when it’s not me but the client that is viewing the PDF? I can’t assume they will know how to adjust these settings.”

This is true, and believe it or not there is a fix you can apply using Adobe Illustrator.

 

1.) Open the logo in Adobe Illustrator and select the letter in question. Notice in this zoomed in screen shot that the lowecase “L” only has four anchor points.

 

 

 

2.) Choose: Object > Path > Add Anchor Points.

 

Simply adding more anchor points will fake out the PDF to display this vector object as is should. Seems crazy, but it is true.

 The resulting logo will look as it should even with “Enhance thin lines” checked or unchecked.