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Suppose I have created a vertical stroke of width 7 px.

Now I need it's width a little more than 7 px, to match the width of a font's letter's width. (I could do it by changing the offset of font after creating outlines, from it, but I'm not doing it because it somewhat destroys the beauty of font). I made the width from 7 px to 7.1 px and it almost matches with font (I noticed this by zooming in artwork).

Now I expand the stroke. The art board size is 1024x768 px. I saved my design and exported it.

(For privacy, I can't show the image here, but I think description should help you understand my question.)

The image looks great but I have 2 queries about quality of design that might have been affected:

  1. Whould my image be more better and crisp had I used a EVEN stroke width (8 px) and changed it to 8.1 px? Does even and odd make any difference?
  2. Is there any actual meaning of 0.1 px in illustrator? How is this 0.1 px is rendered in final PNG image? Or it is ignored?

PS: I didn't see any noticeable difference when I tried above t

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  • You can't have fractions of a pixel in any software which renders a raster image - only whole pixels.
    – Billy Kerr
    Commented Dec 11, 2017 at 11:23
  • If you remember you've answered my other question. There I've explained that when I turn on pixel grid and snap the art to pixels, it looks crisp in PNG. But when I don't, it looks fuzzy. That means there's something like decimal pixel thing which I can't explain, but I believe it exists. What do you say?
    – Vikas
    Commented Dec 11, 2017 at 16:25
  • It may exist in Illustrator as a stroke width for a vector path, but when you render to a raster image, only whole pixels exist.
    – Billy Kerr
    Commented Dec 11, 2017 at 17:30

2 Answers 2

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Yes.

Partial pixels will make a difference when saving/exporting images for the web or digital displays

The web, and all digital displays are built upon a pixel grid of whole pixels. When artwork contains a partial pixel, the rendering engine, whatever that may be, has to determine whether that partial pixel should be rounded up, rounded down, or anti-aliased.

8.1px will most likely be rounded down and displayed as 8px. However, it's not impossible that 8.1px is anti-aliased due to the .1px. Antialiasing would result in a "blend" of sorts between the .1px and the color of pixels neighboring it.

So, imagine you've got an 8.1px black square resting on a white field. That .1px is going to cause the edge of the square to be "blended" between black and white, commonly resulting in 1 pixel of a darker grey at 8px, then 1 pixel of a lighter grey at 9px. So you take an 8.1px square and essentially, un-sharpen the edges and create a 9px image, merely to compensate for that .1px overrun.

This is why Adobe implemented the Align to Pixel Grid feature within Illustrator - to prevent this type of anti-aliasing.

  • If you want edges to remain crisp and sharp when exporting/saving for web, you need to work in whole pixels always.

Now for print work... pixels mean nothing and it makes little to no difference if something is 8px or 8.1px.

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  • Thank you for this awesome answer :) However, I couldn't understand this line "So you take an 8.1px ........... 9px image, merely to compensate for that .1px overrun." Do you want to say that due to anti aliasing 8.1 will become 9px square with fuzzy edges? Or do you want to say that I should make it 9px to prevent anti aliasing?
    – Vikas
    Commented Dec 12, 2017 at 17:37
  • It could be either depending upon what is outputting the image and output settings.
    – Scott
    Commented Dec 12, 2017 at 17:42
  • Thank you. Could you please check the (c) point on this question? It is asked by me. Your answer here cleared my other doubts there but still I'm little confused about outlines created by fonts. graphicdesign.stackexchange.com/questions/102478/…
    – Vikas
    Commented Dec 13, 2017 at 4:39
  • Type is a different animal. If you want pixel perfect type you need to use pixel fonts which are designed to render without anti-aliasing at specific sizes.
    – Scott
    Commented Dec 13, 2017 at 16:28
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  1. No. Negligible. The purpose of vector designs is scalability, there should be no reason for 0.1px to be better or worse for the quality of your image in Illustrator.

  2. Yes. Pixels are a unit of measurement and are rasterized according to the dpi settings in illustrator. 300 pixels per inch for example. A) the 0.1px stroke should translate relatively clean with respect to the output size from illustrator, and B) if someone were to blow up that image and pixelate it, it would distort all of the pixels not just your line. So it isn't ignored per se, but again for relevant purposes, negligible.

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    It might be worth mentioning that "pixels" is not a native measurement unit in Illustrator. Internally, all measurements are done in a real world unit. Any conversion to "pixels" is merely accidental.
    – Jongware
    Commented Dec 11, 2017 at 9:48
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    There is no DPI setting in illsutrator that governs how the pixels render. Its purely the setting in your export. Document raster effect setting is not doing anything about this.
    – joojaa
    Commented Dec 11, 2017 at 12:19
  • Thank you. I have asked another question here graphicdesign.stackexchange.com/questions/102478/… . Although @Billy has answered there but still my doubt is not clear. Could you please check 4 queries there?
    – Vikas
    Commented Dec 11, 2017 at 16:28
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    I disagree with this. #1 may be accurate for print work but is entirely inaccurate for web work. #2 Illustrator has no "dpi settings".
    – Scott
    Commented Dec 11, 2017 at 17:08
  • Thanks. You guys are right & the dpi settings are for raster effects.
    – Chris Bolseng
    Commented Dec 11, 2017 at 17:13

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