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I want to visualize what an image(768x1024) looks like when it's scaled down and tiled. I use Gimp, so I select, ctrl-scale to something small (whateverx180), select, copy, edit/paste as../new pattern (give a name, save), then I open a blank white canvas, and fill with the pattern:

enter image description here

Is it the expected behavior of the tool that I see those seams (the background color filters through) on the edge of the individual pattern?1


1. It doesn't happen with the default patterns supplied. And I can fill the canvas with blue first to avoid it. The affected area parameters don't change the result. I made a comparison using Imagemagick's montage, and it tiles without those seams. I am a beginner.

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    The fill tool doesn't add the seams, they are on your scaled image (try to see the borders with a color picker) and probably are a consequence of the scaling operation. How is the border of the original image? – Paolo Gibellini Oct 6 '14 at 10:21
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    I don't know much about the Gimp, but that is the expected behaviour if your selection tool is anti-aliased. There's normally a checkbox to turn that off. – Stan Rogers Oct 6 '14 at 11:22
  • Thank you for your advice both! @PaoloGibellini Indeed I was focused on the fill and didn't pay attention to the scaling tool - it has an "interpolation" item, containing none, linear, cubic and sinc - it seems selecting none removes those seams. On the other hand I could reproduce this with any dark image from the web; and selecting transparent bg shows lines with varying gray gradients i.e. checkermarks. But scaling indeed. If you make an answer I'll select it. Thanks again. – user29318 Oct 6 '14 at 12:03
  • @StanRogers Thank you, I see you were also spot on as those settings are about anti-aliasing as you suggested... – user29318 Oct 6 '14 at 12:08
  • @Amphiteót You are welcome, I've posted a more formal answer. – Paolo Gibellini Oct 6 '14 at 18:25
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The fill tool doesn't add seams, it simply repeats the pattern putting it as adjacent tiles. The problem could be into the way you have resized your original image.

When you scale a bitmap image, you create a new image with a different number of points, and the information used for the values of the pixels of the new image is obtained using an algorithm (in GIMP you can choose between several formulas).

Depending on the method used, you can obtain different results. Sometimes the operations introduces artefacts (in your case it seems a Moiré pattern).

You can change the scaling method or correct directly the resized image.

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