KB183816172: ArtPro+ - Potential Stroke Miter Issue message appears

Summary

ArtPro+ generates warning messages if there is a risk that stroked objects will be rendered differently by other applications (e.g.: RIP).

Symptoms

ArtPro+ shows one or more "Potential Stroke Miter Issue" messages in the Messages section.

Background

Strokes can have different Corner styles (a.k.a. Join styles): Miter, Round and Bevel.

If the Corner style is Miter, then a Miter limit can be applied to avoid excessively sharp corners: if the ratio between length of the Miter and the Stroke width is larger than the Miter limit, then the corner will be beveled (chopped off):

The ratio miter length / stroke width is related to the angle of the corner, e.g., for φ = 60° it is equal to 2, for φ = 90° it is equal to 1.414.

More information can be found in PDF Reference 1.7 pages 216 and 217.

Example

In an equilateral triangle the ratio miter length / stroke width is equal to 2.

If the Corner style is Miter and the Miter limit is larger than 2, the corners will be mitered:

	miter limit = 2.1

However, if the corner style is Miter and the Miter limit is smaller than 2, the corners will be beveled:

	miter limit = 1.9

In general, a shape may contain corners with different angles (and therefore different Miter lengths). The decision to bevel is made separately for each corner, even if the Miter limit applies to the whole stroke.

Issue

Software applications which "rasterize" stroked objects (either for display on screen, like Adobe^® Illustrator^® or ArtPro+, or for printing, like a RIP) have to decide for each corner of a Miter-style stroke whether that corner has to be beveled or not.

This is achieved by calculating, for each corner, the ratio miter length / stroke width and comparing it to the Miter limit of the stroked object.

As can be seen in the triangle example, a very small change in the Miter limit or in the angle may result in a different decision (Bevel or Miter) with a distinct visible result.

The problem is that in real software numeric calculations are not exact. So, in the case of the triangle with a Miter limit equal to 2, it is not sure whether the result will be mitered (first case) or beveled (second case).

Worse even, in reality one angle could be 59.999° and another maybe 60.001°, resulting in something like this:

	miter limit = 2 (rendered by Adobe® Illustrator®)

However, there is no way of knowing which decisions other applications will make, in case the RIP used for printing. This means that the printed result could be different from the on-screen rendering!

ArtPro+ generates a warning message for each stroked object which has one or more "dubious" corners, i.e., corners for which the ratio miter length/ stroke width is very close to the the Miter limit, possibly resulting in different rendering in other applications.

In the triangle example above, a Miter limit close to 2 would result in such a message.

Solutions

If a stroked object causes a "Potential Stroke Miter Issue" message, different remedies are possible.

1. Make more explicit beveling choices:
   1. Change the Miter limit of the stroke until it has no more dubious corners.
   2. Choosing a higher value for the Miter limit will favor longer miters, choosing a lower value will favor beveling.
   3. Or change the angles of the stroke shape by editing the path (e.g.: using the Pen tool), until it has no more dubious corners.
   4. Or set the corner style to Round or Bevel.
   5. Or, in the case of stroked text, changing the font might help.
2. Convert the stroke to a separate object:
   1. Outline Strokes in the Object menu.
   2. Or apply Divide in the Shaper tool.