Confused about implementation for GIF Dispose Method

莫红波 <[email protected]> Thu, 24 Nov 2016 05:44:57 +0000
Newsgroups gmane.comp.video.graphicsmagick.bugs
Message-ID <CACghtk15o_P9=f1gY0CXcbUxepb0kfeoyBKOBmq0APnF7=j6sA@mail.gmail.com>
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Hi, All:
   I find that the implementation for GIF dispose method in CoalesceImages
isn't based on Graphics Interchange Format, Version 89a
<http://www.w3.org/Graphics/GIF/spec-gif89a.txt>.

     iv) Disposal Method - Indicates the way in which the graphic is to
     be treated after being displayed.

     Values :    0 -   No disposal specified. The decoder is
                       not required to take any action.
                 1 -   Do not dispose. The graphic is to be left
                       in place.
                 2 -   Restore to background color. The area used by the
                       graphic must be restored to the background color.
                 3 -   Restore to previous. The decoder is required to
                       restore the area overwritten by the graphic with
                       what was there prior to rendering the graphic.
              4-7 -    To be defined.

   However in magick/transform.c:CoalesceImages, the dispose method
affects the current frame not the next.
   Did I understand it wrong? Any help would be appreciated.


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<div dir=3D"ltr">Hi, All:<div>=C2=A0 =C2=A0I find that the implementation f=
or GIF dispose method in CoalesceImages isn&#39;t based on=C2=A0<a rel=3D"n=
ofollow" class=3D"inbox-inbox-external inbox-inbox-text" href=3D"http://www=
.w3.org/Graphics/GIF/spec-gif89a.txt" style=3D"color:rgb(102,51,102);paddin=
g-right:13px;font-size:13.5072px">Graphics Interchange Format, Version 89a<=
/a>.=C2=A0<pre style=3D"word-wrap:break-word;white-space:pre-wrap">     iv)=
 Disposal Method - Indicates the way in which the graphic is to
     be treated <font color=3D"#ff0000">after being displayed</font>.</pre>=
<pre style=3D"word-wrap:break-word;white-space:pre-wrap">     Values :    0=
 -   No disposal specified. The decoder is
                       not required to take any action.
                 1 -   Do not dispose. The graphic is to be left
                       in place.
                 2 -   Restore to background color. The area used by the
                       graphic must be restored to the background color.
                 3 -   Restore to previous. The decoder is required to
                       restore the area overwritten by the graphic with
                       what was there prior to rendering the graphic.
              4-7 -    To be defined.</pre><pre style=3D"word-wrap:break-wo=
rd"><font face=3D"sans-serif" style=3D"white-space:pre-wrap">   However in =
magick/transform.c:CoalesceImages, the dispose method affects the current f=
rame not the next.=20
   Did I understand it wrong? </font><font face=3D"sans-serif"><span style=
=3D"white-space:pre-wrap">Any help would be appreciated.</span></font></pre=
><pre style=3D"word-wrap:break-word;white-space:pre-wrap"><br></pre></div><=
/div><div dir=3D"ltr">-- <br></div><div data-smartmail=3D"gmail_signature">=
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