Remove thin lines caused at edges of patterns and vector shapes

[NotMyFault]

Hi,

 

There are many posts complaining about "thin lines" becoming visible under certain circumstances, in Photo, Designer, and Publisher.

• vector shapes touching each other at their edges
• patterns of pixel layers (tiles)

 

The principle cause is anti-aliasing, which is active by default. All pixels at edges of layers will get anti-aliased. The function changes both the color and the transparency (alpha) of edge pixels. This will lead to partially transparent edge pixels. Depending on background layers, this often creates a line of of pixel width in light colors shining through. This can be very distracting in case of seamless patterns.

To remove the thin line, there are multiple options. Unfortunately, most recommended options do additional collateral damage:

• Deactivating anti-aliasing, or modifying the coverage map, is global per layer and could lead to rough edges.
• Adding back-fill layers manually is very tedious

There is a new simplified method, suitable when your document is pixel art, or will / can be rasterized at export.

Steps:

• add a levels adjustment
• select the alpha channel
• set the white level to 75% (depending on blend gamma of the pattern layers, you may need to use 50% in case of blend gamma 1.0).

In Photo, you can save this as preset for later re-use in other documents.

Whow does this work?

• assuming you patterns / layer are fully opaque, and using default blend gamma of 2.2
• Anti-aliasing will create edge pixels with a known range of alpha values: 75% to 100%. Values from 0% to 75% will only occur at edges where pattern do not face each other.
• The curves adjustments ensures all alpha values above 75% will reach 100%, thus effectively removing the thin line, and replacing it by the blend of the colors of neighboring pixels
• There is a minor collateral damage. These alpha values (75%-100%) may occur in other places. But the visual difference is small, and will be far less disturbing compared to a white line inside a seamless pattern.

Example of distracting thin lines / background shining through:

harsh edges when deactivating AA:

Thin lines removed, while keeping AA active (with limited effect to alpha channel):

AA on edges stays intact in general (reduced alpha)

Requires settings in levels adjustment:

[John Rostron]

Thanks @NotMyFault. It is good to see a straightforward tutorial using words and pictures without recourse to using video.

John

[Lorox]

I have this very problem with my Affinity Designer artwork (AD v. 1.9.3 on Mac OS Mojave) . Even if shapes (i.e. simple rectangles which are not rotated) are positioned abslutely pixel perfect flush to each other I'll get those thin lighter lines when exporting my artwork to pixel formats (say JPG). This actually has been some kind of a problem right from the start in AD years ago.

It's even visible pre-export in most zoom values while still in Designer.

As I'm in Designer I unfortunately don't have Adjustment Layers to try the method described here... Any ideas about what might be done to get proper exports?

[Lorox]

I'm adding two screenshots here: one from inside Designer at 800% zoom which actually doesn't show those fine lines (and the grain/noise looks finer) and another from the exported JPG (full resolution of a 300dpi AD file), also viewed at 800% zoom.

[NotMyFault]

@Lorox

Could you please open a separate thread under questions, to keep this tutorial thread focused?
i‘m happy to investigate deeper if you are able to upload the afdesign file there.

As i see you are probably use a noise filter, which might causer the issue. Some filters cause „fluctuations“ on alpha channel interfering with the issue. There are other causes of thin lines independent from alpha. Curious to find out 😉

[Lorox]

@NotMyFault

I've done according to your suggestion:

As to the noise filter (it's actually just „Noise“ added to the fill in the Colour Studio/Palette): as it happens it really doesn't make any difference if it’s a fill with or without noise – the lines will appear all the same...