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Is there a technical term to designate stray pixels (like clearly visible dots near contours) in raster graphics ? I seem to remember the word "kayatutu" from early Macintosh days but perhaps it was just a buzzword.

Edit: Here's an example with some clipart (zoom in to see the grey dots).

enter image description here

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I use "schmutz." –  Lauren Ipsum Jul 25 '12 at 1:50
    
Is there a reason why the term "stray pixel" is itself insufficient for your needs? If you could explain why, that might give more context so as to be able to answer your question accurately. –  Dave M G Jul 26 '12 at 13:47
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Thanks for the added example. In the picture of the dog, what is happening is that the stray pixels are the result of JPG compression (possibly combined with the white not being as pure as you thought before saving to JPG format). The compression algorithm is trying to reconcile the negative white space around the dog with all the colour within the dog, because JPG compression is looking for the best average colours across wide spaces. As in my answer, I would definitely call these "artefacts", but, again, please note that "artefacts" can also have other causes, such as bad aliasing. –  Dave M G Aug 14 '12 at 17:17
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3 Answers 3

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I refer to them as artifacts. The term is general for lots of different types of distortion, but the kind of stray pixels you are talking about could be the result of a number of causes, so for a more specific term you'd need a more specific situation.

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Based on the newly added sample photo, this is the correct answer. It's typically referred to specifically (in the case of JPGs) as compression artifacting or JPG artifacting and is a result of how lossy JPG compression works. –  DA01 Aug 14 '12 at 6:18
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"Scum Dot" is the most common phrase I've heard in the printing industry.

I don't believe I've heard anything other than "Stray pixel" for on-screen work.

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"stray pixels (like clearly visible dots near contours) in raster graphics" is called aliasing

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I'm not sure this would be a correct use of the term aliasing. Aliasing is not always undesirable, and does not always result in "stray" pixels. –  Dave M G Jul 26 '12 at 13:45
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I think Horatio's thinking of jaggies, and I think that's not what's being asked about. –  user568458 Aug 1 '12 at 16:34
    
There is a lot of ambiguity in language, and a picture is worth more than words in this instance. In the example you give it is certainly "artifacts" or "artifacting." It looks like jpeg quantization, and then someone used a magic wand tool to remove the white background, leaving slightly non-white areas. "Jaggies" is not a technical term. –  horatio Aug 14 '12 at 15:12
    
@DaveMG: you are assuming that "stray pixel" has a defined distance, but a non-technical user might certainly describe non-smooth curves as having stray pixels. In any event the question has been clarified with a photo. –  horatio Aug 14 '12 at 15:15
    
@horatio: Distance has nothing to do with it. The point is that "aliasing" is not an error. It's a feature that is sometimes useful and sometimes not depending on the desired outcome. The OP is asking about a problem, when pixels have undesired visibility. They may be the result of badly done aliasing, but aliasing is not, in itself, the problem or the description. –  Dave M G Aug 14 '12 at 17:11
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