[FFmpeg-trac] #5559(undetermined:new): IFF ANIM: fix decoding artefacts (ANIM-J)

FFmpeg trac at avcodec.org
Sun May 15 15:28:35 CEST 2016

#5559: IFF ANIM: fix decoding artefacts (ANIM-J)
             Reporter:  ami_stuff    |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0

Comment (by ami_stuff):

 anim/laserboing ... 320 x 400 x 6 Movie oneway, 4 frames.
 anim/notboingagain ... 352 x 440 x 6 Movie reversible, 146 frames.
 anim/spigot ... 352 x 440 x 6 Movie reversible, 54 frames.

 read also readme file from this archive:



 This program calculates the differences between two images and stores
 the result as a delta file.  The program is called with the names of
 three files:

         dilbm image1 image2 delta

 The two image files must exist.  The delta file will be created.  The
 delta file represents the data required to convert image1 into image2.
 It is not reversible.

 There is an alternate delta format that is reversible, to generate it,
 add an 'x' at the end of the command:

         dilbm image1 image2 delta x

 Normally, dilbm will display a picture of the differences between the
 images.  To suppress this picture, add a 'q' at the end of the command,
 this will make dilbm run slightly faster.


 This program packs delta files together to create an animation.  It
 takes a single argument that is the name of a text file that contains a
 description of the animation.  The following format must be followed:

           1     a     The name of the animation that is to be produced.
           2     i     The name of the initial image.
           3     d0    The name of the initial delta file.
           4     d1    The name of the first delta file.
           5     d2    The name of the second delta file.
           n+3   dn    The name of the last delta file.
           n+4   *     An asterisk to denote the start of sequence control
           n+5   m t   m is a delta number and t is a time delay
           n+6   m t
                 m t

 The animation works by double buffering, so you must specify two images.
 The file 'i' specifies the first image.  The delta file 'd0' defines the
 second image in terms of the first.

 The delta file 'd0' is discarded after the second image file is
 constructed.  The remaining delta files, d1 to dn are stored in memory.
 When the animation is replayed, the following actions take place:

 The first image is displayed on the screen.  Then the second image is
 displayed.  While the second image is displayed, the first image is
 changed with a delta file.  Then it is displayed while the second image
 is modified with another delta file.  This process is repeated.

 The sequence control determines the order in which the delta files are
 used.  The value 'm' determines which delta file is to be used.  The
 value t specifies how much time (in jiffies) is to be used for the
 change.  If t is negative, then m is used to indicate a transfer to the
 m'th m-t pair.  Thus the following sequence

                 3  2
                 5  2
                 9  2
                 12 2
                 2  -1

 would stand for the following sequence of delta files:

         d3 d5 d9 d12 d5 d9 d12 d5 d9 d12 d5 d9 d12 etc.

 Not all delta files need to be used (although that would be wasteful)
 and some may be used many times, if the sequence control specifies a

 Deciding which images to use to construct delta files, and the correct
 sequence of delta files is complicated because of the nature of double
 buffering.  Here is an example, suppose that we wish to display images
 in the following sequence:

         15 14 13 12 11 10 9 8 7 8 9 10 11 12 13 14 15 14 13 12 11 etc

 then we can use the 'x' type of reversible deltas and compute the
 following files (it is a good idea to place the dilbm commands in a text
 file and use an 'execute' command).

 dilbm  pic15.image pic14.image dx15-14 x q
 dilbm  pic15.image pic13.image dx15-13 x q
 dilbm  pic14.image pic12.image dx14-12 x q
 dilbm  pic13.image pic11.image dx13-11 x q
 dilbm  pic12.image pic10.image dx12-10 x q
 dilbm  pic11.image pic9.image  dx11-9  x q
 dilbm  pic10.image pic8.image  dx10-8  x q
 dilbm  pic9.image pic7.image   dx9-7   x q
 dilbm  pic8.image pic8.image   dx8-8   x q
 pilbm  buildx.script

 The file buildx.script contains the following:


 1 2
 2 2
 3 2
 4 2
 5 2
 6 2
 7 2
 8 2
 7 2
 6 2
 5 2
 4 2
 3 2
 2 2
 1 2
 8 2
 1 -1

 Note that the delta file dx8-8 causes no action to take place, so it is
 also used in place of dx14-14.

Ticket URL: <https://trac.ffmpeg.org/ticket/5559#comment:2>
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