Legacy ImageMagick Discussions Archive

I am converting a movie from ntsc to pal, the subtitles (as the movie) need to be converted from the resolution of 720x480 to 720x576.

The subtitles are 8bits png files with at most 4 colours (one being the transparency), to convert all the files I used:

Code: Select all

for d in *.png ;do
convert "$d" -resize '720x576!' -colors 4 tmp.png || break
mv tmp.png "$d"
done

Unfortunately every subtitle file must use the _same_ four colours.
Using convert this way the four colours in each file can be (and are) different.

How can I force convert to maintain the original colours or how can I set the palette?

Thanks.

see -map

http://www.imagemagick.org/script/comma ... s.php?#map
http://www.imagemagick.org/Usage/quantize/#map
http://www.imagemagick.org/Usage/video/#gif

If you resize using -sample only the original colors will be used. But at a loss of quality!

The other method as pointed out by fred, is to re-map the image to just the four colors desired. You may or may not want the dither for this (turn of dither with +dither)

To anyone interested:

You can convert your DVD subtitles from one resolution to an other extracting them with

Code: Select all

tccat -i /dev/sr2 -T 8,-1 | tcextract -x ps1 -t vob -a 0x20 > subsen
mkdir subtitles
cd subtitles
subtitle2pgm -i ../subsen -c 224,224,32,0 -g 4 -t 1 # <-- verify the vaules of -c they depends on the movie(1)

convert all the png files with

Code: Select all

for d in *.png ;do
  convert "$d" -resize '720x575!' +dither -map "$d" tmp.png || break
  mv tmp.png "$d"
  echo "$d"
done

mixing them in the mpg file with the movie with

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spumux -s0 movie_subtitle.dvdxml <../movie.mpg >../movie_wsubs.mpg #<-- increase the -s value if it is not the first subtitle

and finally you can author your dvd with the mpg file.

About (1)
I usually use `-c 0,85,170,255' to see how is the palette and assign black to the background, white inside the letters and dark gray around.

Thanks everyone.

Legacy ImageMagick Discussions Archive

Resize without altering the palette (solved)

Resize without altering the palette (solved)

Re: Resize without altering the palette

Re: Resize without altering the palette

Re: Resize without altering the palette