Ghost Lines in Repeat Patterns: Causes, Checks and Fixes

What a ghost line looks like

You see a thin line, lighter or darker than the pattern around it, at the same interval across the print. It follows the edges of your tile: horizontal lines at the top and bottom join, vertical lines at the left and right join. In a half-drop repeat, the vertical lines step down by half a tile.

Common causes

• ›Anti-aliasing at the tile edge. The software blends the edge pixels with the empty area outside the canvas, so the edge comes out slightly lighter or partly transparent.
• ›Artwork that does not continue across the edge. A motif cut by the right edge must continue exactly on the left edge, and the same for top and bottom.
• ›Scaling after the tile is made. Resizing by a factor that is not a whole number resamples the edge pixels, so the two edges stop matching.
• ›Odd pixel sizes in a half-drop repeat. A tile with an odd height cannot drop by exactly half, so one row is a pixel out.
• ›Vector exports. Pattern tiles that are not aligned to the pixel grid can export with a hairline gap or overlap.
• ›Compression and colour conversion. JPEG compression and some colour conversions treat the edges differently from the middle of the image.

How to check your tile in Photoshop

1. 01Open the final tile at its print size.
2. 02Choose Filter, then Other, then Offset.
3. 03Set Horizontal and Vertical to half the canvas width and height, in pixels. Select Wrap Around.
4. 04Zoom to 100% and look at the cross in the middle of the canvas. That cross is where your tile joins.
5. 05Undo the offset before you save, or fix the joins in the offset view and then offset back.

Also test a larger area. Define the tile as a pattern and fill a canvas three tiles wide and three tiles high. Lines are easier to see over a bigger area.

How to fix ghost lines

• ›Make the tile at its final pixel size, so you never need to scale it later.
• ›If you must scale, use a whole number (200% or 300%) with Nearest Neighbour resampling, so the edge pixels stay the same.
• ›Use the offset view to clone or heal across the joins, then offset back.
• ›Remove transparent or semi-transparent pixels at the edges. The artwork must fill the canvas right to the edge.
• ›For a half-drop repeat, use an even tile height.
• ›Save repeat tiles as TIFF or PNG. JPEG compression can add marks at the edges.

How the AOP101 audit checks for ghost lines

The free audit compares the colour change across each join (top to bottom and left to right) with the normal colour change between neighbouring rows and columns inside your tile. It measures colour difference with CIEDE2000 (ΔE 2000), a standard way to measure how different two colours look to the human eye.

A join that changes much more than the inside of the tile is flagged. A busy pattern is not flagged only because it is busy.

The check runs in your browser. Your file is not uploaded. Chrome and Edge cannot decode TIFF pixels, so for a TIFF file this check shows NOT VERIFIED. To run it, audit a PNG copy of the tile.