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VIDEO.md

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How to make video with CHART/COUPE ?

General ideas:

  1. Prepare a script which produces a nice image :), loop on time to produce a time series of images, in native NCL format (cgm)
  2. Transform cgm file into raster type file, using ctrans (NCL) and convert (ImageMagick)

Example:

ctrans -d sun -res 1024x1024 file.cgm \> file.sun 
convert file.sun file.gif

Note that convert offer various option to control the quality of the raster image (-density -quality etc... ). Note that I use gif format because I want to produce animated gif video ans a starting point.

  1. Produce the video using gifsicle program (assuming that at this stage you have a bunch of files correctly ordered.)

Example:

gifsicle -d0 -l0 file*.gif > animation.gif

Note that -d0 force the shortest delay between frames, -l0 force the animation to loop infinitely. For slowing down the movie you can use -d nn (nn is a delay in miliseconds).

Note that delay and loop parameter can easily be changed directly on the animation.gif file :

gifsicle -b -d10 -l20  animation.gif

Advanced tricks:

reshaping the images:

gifsicle offers the possibility to crop part of the image into another image.

gifsicle --crop X1,Y1-X2,Y2 file_in.gif > file_out.gif

ImageMagick display tool is usefull for determining the crop windows (X1,Y1-X2-Y2) (in pixel).

Assembling images in a mosaic of images:

ImageMagick montage tool does the job :

Example:

montage -tile 2x1 -geometry 950x500 file1.gif file2.gif montage.gif

-tile define the layout of the mosaic. -geometry gives the dimension of each tile.

Using transparency:

  • In CHART use the -spback option to use the background color for the missing values.
  • Then once the resulting image is in gif, you can transform the backgroud color to be transparent, using gifsicle :

Example:

gifsicle -t 0 file_in.gif > file_out.gif

  • In order to overlay an image with transparency over another image, composite tool from ImageMagick can be use : Example:

    composite file_transparent.gif file_background.gif composite.gif

  • gif image format does not support a gradual opacity. So in order to fully use opacity control, you need to transform your images in png format (for example), using convert:

Example:

 convert image.gif image.png
  • then the compsite tool can be use with specific opacity options (-dissolve) :

Example:

composite -dissolve 70% file_transparent.png file_background.png composite.png
  • you can come back to gif (for using gifsicle) just by convert again

Example:

convert composite.png composite.gif
  • Of course when using transparency, you must take care in the image preparation so that no text or unwanted features (colorbar, label etc... ) interfere between superposed images.