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Bug introduced in V11.1 and fixed in V11.2

What happened? Is this a regression or maybe some default options were changed?

Test case:

Graphics3D[Sphere[]] // Export["Test.gif", #] &

GIF comparison

Comparison 11.1.1 vs 10.4 on Windows 10.

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    $\begingroup$ Eek... any impact on the file size? $\endgroup$ – Yves Klett Aug 21 '17 at 8:34
  • $\begingroup$ @YvesKlett FileByteCount /@ {"11.gif", "10.gif", "11.png", "10.png"} -> {18493, 28635, 41518, 42317} $\endgroup$ – Kuba♦ Aug 21 '17 at 8:35
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    $\begingroup$ About the file sizes: Dithering introduces noise to smoothen the appearance of gradients. Noise doesn't compress well. I would expect a dithered GIF (containing smooth gradients) to be significantly larger than a non-dithered one. If it weren't for @ChipHurst's comment I would say that the reason to change Automatic to non-dithered could only be file size reduction. $\endgroup$ – Szabolcs Aug 23 '17 at 12:01
  • $\begingroup$ @Szabolcs That would have been my guess too. $\endgroup$ – Chip Hurst Aug 23 '17 at 20:45
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I talked to the relevant developer and it turns out this is indeed a regression.

It looks as if the default "DitheringMethod" changed from "FloydSteinberg" to None.

Compare "DitheringMethod" pointing to None, Automatic, and "FloydSteinberg" in 10.4 and 11.1:

Table[Labeled[
    ImportString[ExportString[Graphics3D[Sphere[]], "GIF", "DitheringMethod" -> d]], 
    {$VersionNumber, d}, Top], 
  {d, {None, Automatic, "FloydSteinberg"}}
]

enter image description here enter image description here

In 10.4:

$VersionNumber

10.4

Equal[
 ImportString[ExportString["Graphics3D"[Sphere[]], "GIF"]],
 ImportString[ExportString["Graphics3D"[Sphere[]], "GIF", "DitheringMethod" -> "FloydSteinberg"]]
]

True

In 11.1:

$VersionNumber

11.1

Equal[
 ImportString[ExportString["Graphics3D"[Sphere[]], "GIF"]],
 ImportString[ExportString["Graphics3D"[Sphere[]], "GIF", "DitheringMethod" -> None]]
]

True
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    $\begingroup$ Was that intentional? $\endgroup$ – Kuba♦ Aug 21 '17 at 14:49
  • $\begingroup$ I don't know. Just something I observed when looking through the export options of GIF. $\endgroup$ – Chip Hurst Aug 21 '17 at 14:50
  • $\begingroup$ Thanks. Is anybody around you could ask or should I ask support? :) $\endgroup$ – Kuba♦ Aug 22 '17 at 6:54
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    $\begingroup$ I talked to the relevant developer and it turns out this is indeed a regression. $\endgroup$ – Chip Hurst Aug 23 '17 at 3:26
  • $\begingroup$ Thanks for forwarding it. $\endgroup$ – Kuba♦ Aug 23 '17 at 5:33

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