Sides of letters look like spiral rope.

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Billink
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Joined: Sat Aug 18, 2018 9:32 am

Sides of letters look like spiral rope.

Postby Billink » Sat Aug 18, 2018 10:38 am

I'm having a problem getting crisp lines in my letters on straights and curves. I'm working on a 2018 Mac, 10.13.6. The example letter here is a W in Courier Normal Regular. (But it happened with Courier Bold Bold and Courier that I altered with the Bezier Tool) The Stroke is 1.0, but happens at any stroke. The letter is 280w x 300h px.Image. Here's what the nodes look like: Image. I've saved it as a .svg, .eps, .png and brought it to a season pro on AI and saw the problem on all 3 saves but couldn't determine why. Any help or advise would be greatly appreciated? Hope it's not my video card.
Billink

v1nce
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Re: Sides of letters look like spiral rope.

Postby v1nce » Sat Aug 18, 2018 9:58 pm

This is caused by aliasing or rather antialiasing in this case.

The image is a matrix of dot. You can't break down the dot and sometimes "mathematically" you face the problem of the color you should give to the dot : if the black line goes through the dot but it only fills 33% of the dot and the white fills the other 67%, which color should you use ? The two main solutions are : fill it with white (because this is the main color) of fill it with a mix of 33% black and 67% white = light gray.

Inkscape use the last solution.
What you call "rope" effect are the gradients that go from black to white .

I spotted some areas when you can see them.

MUWkDOS.png
MUWkDOS.png (22.52 KiB) Viewed 2550 times


It is more noticeable when lines are near of (but not equal to) horizontal or vertical.
It is even more noticeable because of the length of the line.

There's very little things you can do.
Maybe you can upscale your letter, apply blur then downscale it. But il will smooth your image and not make it more crisp.

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brynn
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Re: Sides of letters look like spiral rope.

Postby brynn » Sun Aug 19, 2018 1:16 am

That bumpy appearance might be less noticable if you remove that thin black stroke. In this case, the stroke might be emphasizing this known phenomenon. (with emphasis on "might" - I didn't test)

Billink
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Re: Sides of letters look like spiral rope.

Postby Billink » Sun Aug 19, 2018 8:21 am

I thought vector in inkscape wouldn't have a problem like this, with the dots?? So, no one can produce large letters like this for logos in inkscape with clean crisp lines? I find this hard to believe.

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druban
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Re: Sides of letters look like spiral rope.

Postby druban » Sun Aug 19, 2018 6:23 pm

I was hoping someone with some Mac experience would help you out here but so far not. I don't use Macs either but I believe you are seeing an Inkscape and mac compatibility issue where a low res pixelated image is displayed until you set some control panel checkbox. is it a quartz issue maybe I recall that being mentioned some time back
One way to check is if the problem gets worse as you zoom in, if not then you are just seeing the limitations of the pixels in your display
perhaps you could search for mac and aliased rendering in the forum
Your mind is what you think it is.

tylerdurden
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Re: Sides of letters look like spiral rope.

Postby tylerdurden » Mon Aug 20, 2018 5:02 am

I'm not sure you're seeing anything out of the ordinary. As stated above, zoom in and see if the perceived artifacts zoom as well.

Image
Have a nice day.

I'm using Inkscape 0.92.2 (5c3e80d, 2017-08-06), 64 bit win8.1

The Inkscape manual has lots of helpful info! http://tavmjong.free.fr/INKSCAPE/MANUAL/html/

Billink
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Re: Sides of letters look like spiral rope.

Postby Billink » Mon Aug 20, 2018 1:44 pm

Let me first say that I really appreciate people taking the time to help me out here.
When I zoom in, the problem does seem to go away, but when I'm viewing it at 1:1 and the letters are at the correct size to be viewed at, I get the spiral roping. As said in my first post, I took it to a pro I know. He is on the most updated mac with the best video cards on a very big system that hosts 100 in-house mac designers. They all use AI. He opened my files that I saved in .svg, .eps and .png and he saw it, as well. His lines never come out like that. It is an actual problem that is staying engrained in the file. I was hoping it was just my perception on my computer and that it displayed correctly on other computers, but that was not the case. After more testing, without a stroke the problem is very less noticeable:ImageThe next test is the W at 3" high, 1" high and 1/2 high with a stroke of .5. Problem is noticeable at all heights. Next I did a test with rectangles at different angles. I think I am narrowing the problem down. ImageI am only seeing the problem at positions 2,3,4,10 and 11. All other positions are clear and crisp. As the line approaches verticle or horizontal, it can't hold it's true shape of a line. Hmm. Why is that????

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druban
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Re: Sides of letters look like spiral rope.

Postby druban » Mon Aug 20, 2018 2:01 pm

can you send us this file that your friend looked at? Also, a professional workstation will probably have a high end display with sharper rendition then yours. Anyway we could look at your file, but right now I am leaning towards saying this is normal for screen display.
However! When you save as eps or png the vector is converted to pixels and that resolution is probably set low, causing these artifacts. The default is screen res but that should be raised to 300 dpi e.g. for sharpness

We are probably having some confusion about terms vector and pixel and resolution and picture
Your mind is what you think it is.

v1nce
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Joined: Wed Jan 13, 2010 4:36 am

Re: Sides of letters look like spiral rope.

Postby v1nce » Tue Aug 21, 2018 1:04 am

AFAICT this is normal.
Even if inkscape is a vector program, at the very end the image should be turned into a bitmap to be displayed on a screen.

aliasing.png
aliasing.png (1.28 KiB) Viewed 2392 times


Inkscape (and 99% of vector program) will apply an antialiasing filter to smooth out the results.

antialiasing.png
antialiasing.png (1.76 KiB) Viewed 2392 times



Antialiasing could be avoided for horizontal and vertical.
AA works very well for some special angles (45 (=atan(1) , 26.6 (=atan(0.5)) , 18.4 (=atan(1/3)) and so on )
AA works well for angles > 20 and < 70.
AA becomes quite noticable for angle near horizontal (or vertical)


> When I zoom in, the problem does seem to go away

No, it's probably a eye/mind "illusion". Whatever the zoom factor is, inkscape will always draw the line the same way. Some pixels will be entirely in (or out of) the stroke and some will be only partly covered by the stroke. And (AFAICT) inkscape will always process the problematic pixels the same way. So why is it this doesn't feel the same when you zoom in ? I suppose this is because :
1) the stroke becomes larger.

At 1:1 your eye sees :
green,...,green
[discontinuity A spreading for x pixels]
black
[discontinuity B spreading for x pixels]
white,..., white

x pixels = length of gradient to go from green to black. It depends of angle. (0 for horizontal or vertical, 1 for 45, "infinite" (or rather length of line) for near horizontal)

But your brain sees green, dicontinuity of 2x pixels,white


At 10:1 your eye sees :
green,...,green
[discontinuity A]
black,black,black,black,black,black,black,black,black,black,
[discontinuity B]
white, ..., white
What is the length of dicontinuity A ? It is still x pixels wide and not 10x.

And your brain sees green area [discontinuity A] black area [discontinuity B] white area
I guess it hurts less to see smaller discontinuities between large areas than a large discontinuity between small areas


2) the image becomes simpler

The more you zoom on your letter, the less of it you can see. If you zoom on a peculiar leg, you'll see this leg as a green area over a white background ; the others legs won't be in the picture. So I guess your brain will see two areas and won't bother you with discontinuities in between. While those discontinuities could be interesting in the more complex shape it was at 1:1.

phiscribe
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Re: Sides of letters look like spiral rope.

Postby phiscribe » Tue Aug 21, 2018 6:58 am

Great detailed overview and in depth commentary on this topic v1nce. Have to bookmark this

Lazur
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Re: Sides of letters look like spiral rope.

Postby Lazur » Tue Aug 21, 2018 7:12 am

Side related, since mac was mentioned:
if you are working with texts in a text editor, that operation system renders the text differently than windows.
It's another case of anti-aliasing, or to be more precise, hinting. As far as I know mac renders letters "fatter".
Maybe that's the reason why the text in inkscape converted to a path (?) looks off (?)*.
A Closer Look At Font Rendering

*-At this moment I'm not sure if that professional setup could render a different result. Can you also share an export from that instance which looks as expected?

v1nce
Posts: 696
Joined: Wed Jan 13, 2010 4:36 am

Re: Sides of letters look like spiral rope.

Postby v1nce » Tue Aug 21, 2018 10:03 am

for those interested two links that explain how the lines are drawn (= how to go from vector to bitmap world)

the aliased version
https://en.wikipedia.org/wiki/Bresenham ... _algorithm

the antialiased version
https://en.wikipedia.org/wiki/Xiaolin_W ... _algorithm


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