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Re: Export Gif animation bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39159] Re: [mg39148] Export Gif animation bug?
  • From: Dale Horton <daleh at wolfram.com>
  • Date: Fri, 31 Jan 2003 19:57:18 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

The color problems are in the colormap of the GIF. There are 
ConversionOptions that control the colormap. Either can be used to fix this 
problem.

By default, a single colormap is used for the entire animation. You can 
create a colormap for each frame with

Export[..., ConversionOptions -> {"GlobalColorReduction" -> False}]

Or you can override the automatic colormap with one of your own. Here's an 
example using "web safe colors".

Export[..., ConversionOptions -> {"ColorReductionPalette" ->
    Table[RGBColor[i, j, k], {i, 0, 1, 0.2}, {j, 0, 1, 0.2}, {k, 0, 1, 0.2}]}]

At 03:37 AM 1/31/2003, Don Taylor wrote:
>I think I've found a bug in exporting GIF animation
>(Mathematica Version 4.0.2.0 under Windows 98 with MS patches)
>
>I don't know what the problem is with this.  I've trimmed down what
>I'm doing to what seems to be the bare minimum that shows the bug.
>Tiny changes in the value of z or in the step size for the table
>will make the background of the gif dark black or brilliant green,
>change the resulting file size by a factor of 16x, etc.  These three
>examples show a sample of the range of behavior that I've seen with this.
>
>This simulates some axes and then draws a moving point which is
>colored green at the bottom of each cycle and black elsewhere.
>
>All these examples are identical code, except for the value of z.
>It takes a couple of minutes to generate each example.
>
>111 kbytes and what seems to be pretty much a correct plot
>
>z = 1; Export["1.gif", Table[Graphics3D[{
>         Line[{{0, 1, 0}, {0, -1, 0}}], Line[{{0, 0, z}, {0, 0, -z}}],
>         Line[{{0, 0, 0}, {4Pi, 0, 0}}],
>         If[Sin[t] <= -0.8, RGBColor[0, 1, 0], RGBColor[0, 0, 0]],
>         Point[{t, Cos[t], z Sin[t]}]},
>       PlotRange -> {{0, 4Pi}, {-1.05, 1.05}, {-1.05z, 1.05z}},
>       ImageSize -> 800, Boxed -> False], {t, 0, 4Pi, Pi/16}], "GIF"]
>
>1598 kbytes! with bright green graph and lots of artifacts scattered
>across the entire graph as it displays
>
>z = 2; Export["2.gif", Table[Graphics3D[{
>         Line[{{0, 1, 0}, {0, -1, 0}}], Line[{{0, 0, z}, {0, 0, -z}}],
>         Line[{{0, 0, 0}, {4Pi, 0, 0}}],
>         If[Sin[t] <= -0.8, RGBColor[0, 1, 0], RGBColor[0, 0, 0]],
>         Point[{t, Cos[t], z Sin[t]}]},
>       PlotRange -> {{0, 4Pi}, {-1.05, 1.05}, {-1.05z, 1.05z}},
>       ImageSize -> 800, Boxed -> False], {t, 0, 4Pi, Pi/16}], "GIF"]
>
>72 kbytes with entire graph nearly completely black
>
>z = N[\[ExponentialE]]; Export["e.gif", Table[Graphics3D[{
>         Line[{{0, 1, 0}, {0, -1, 0}}], Line[{{0, 0, z}, {0, 0, -z}}],
>         Line[{{0, 0, 0}, {4Pi, 0, 0}}],
>         If[Sin[t] <= -0.8, RGBColor[0, 1, 0], RGBColor[0, 0, 0]],
>         Point[{t, Cos[t], z Sin[t]}]},
>       PlotRange -> {{0, 4Pi}, {-1.05, 1.05}, {-1.05z, 1.05z}},
>       ImageSize -> 800, Boxed -> False], {t, 0, 4Pi, Pi/16}], "GIF"]
>
>I searched newsgroup postings and Wolfram and didn't find any mention
>of such behavior.  I presume this is a bug in the gif export code.
>
>If anyone can confirm that this is a bug and that it has been fixed
>that would be good.  If anyone can describe a dependable workaround
>for the moment that would be even better, waiting a good part of
>an hour for an animation to grind out and then discovering that it
>is another "black cat in a dark room" is getting a little old.
>
>Thank you

-Dale



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