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See below image, then read on...

Unbelievable inaccuracy

Previously this circle was 76 pixels diameter.

I changed it to 64 by manually entering it into the W: container, then tabbed, expecting 64 to appear in the H: container.

But no... I got this odd number.


How do I get it back to not doing stupid things like this?

  • It used to be accurate
  • I haven't changed anything
  • There's nothing turned on that wasn't on before


share|improve this question
Do you have "Snap to Grid" enabled? – JohnB May 15 '14 at 21:08
.. Or Align to Pixel Grid enabled? – Scott May 15 '14 at 21:20
up vote 2 down vote accepted

"Use Preview Bounds" is probably enabled.

I can recreate what's happened to you consistently by having this setting on.

If I turn "Use Preview Bounds" OFF ( ⌘K or ⌃K and UNCHECK "Use Preview Bounds"), then miscalculations such as this don't occur.

Also in my testing:

  • It doesn't matter if "Align New Objects to Pixel Grid" is turned ON at document creation or I enable it per object in the Transform palette (⇧F8), or I ignore it entirely
  • It doesn't matter if "Snap to Grid" is ON or OFF
  • It doesn't matter if Scale Strokes & Effects is ON or OFF
  • I can correct an object with this problem only by disabling "Use Preview Bounds", then selecting the object, and then disabling "Constrain Width and Height Proportions" and typing new values into the Transform palette.
  • It happens to any path (simple, compound, or Pathfinder-created compound)

My test went like this: (Using Macintosh Illustrator CC 17.1.0):

  1. No documents open, Illustrator > Preferences (⌘-K) > Use Preview Bounds: OFF

  2. Create a new document 100px × 100px, Units: Pixels, Color Mode: RGB,Raster Effects: 72ppi, Preview Mode: Default, Align New Objects to Pixel Grid: OFF

  3. Draw a circle an arbitrary size (hit L and then Shift-Click-Drag). Mine came out at 59.425 px
  4. With "Constrain Width and Height Proportions" ON, adjust size of circle using transform palette, so it's a true pixel dimension (I chose 50px)
  5. Hit ⌘-K (Illustrator > Preferences) and toggle the Use Preview Bounds: ON. This resized my circle to be 51 px × 51 px.
  6. Type a new Width in the Transform palette (Constrain Proportions still on, I chose 30) and Tab to the next field, - in my case H was set to 29.986px

And then I tried variants of of align to pixels etc…

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I was able to repeat the effect through switching Preview Bounds option on/off. What do you think about the importance of the issue - when it should play some negative role? – Ilan May 16 '14 at 3:44
There's no way known, Jon, that this is the first time you've seen this issue. THANK YOU! This immediately brings to mind 2 questions. What is "Use Preview Bounds" all about, and how did I turn it on? Because I've NEVER turned this on, knowingly, or its been on the whole time and only playing silly now. – Confused May 16 '14 at 4:55
I have to say this is still bugging me because the other night I was drawing and I encountered the same issue, and I never use "Use Preview Bounds". But now, for the life of me, I can't make the problem manifest in any way but the way I described above. – Jon May 16 '14 at 5:19
Oh yeah: "Use Preview Bounds" is a setting to make Illustrator show the bounding box on an object INCLUDING strokes and/or effects. Often useful if aligning objects that look misaligned because of drop-shadows for example. – Jon May 16 '14 at 5:28
" "Use Preview Bounds" is a setting to make Illustrator show the bounding box on an object INCLUDING strokes and/or effects." Argh... so the problem is caused by it calculating/accommodating Anti-aliasing variances? Might make sense... (NOT!) But as you, I'm mystified by it somehow deciding to cause grief, having never come across this before and I – Confused May 16 '14 at 17:27

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