[magick-users] Converting to RGBA Question.

[Anthony Thyssen]

Chris Howell on  wrote...
| Hi All,
| 
| I am still struggling to convert a JPG to rgba my command looks 
| something like this
| 
| convert demo.jpg -channel rgba -matte -transparent black demo.rgba
| 
| Now my original file is 512x512 I would expect my output file to be 1M = 
| 512 x 512 x 4 (rgba)  however my file is 2M any ideas ?
| 
-transparent implies -channel RGBA

However as I have said repeatally about JPEG!!!

  JPEG losses information degrading images when saved.
  Use some other format for intermediate images during processing.
  Only use JPEG format, for the final image, not for further processing.

See IM Examples...    http://imagemagick.org/Usage/formats/#jpg

As such your 'black' may not be a pure black!

Add a small 'fuzz' factor

   convert demo.jpg -matte -fuzz 1% -transparent black demo.rgba

Even so. your image will probbaly not come out good due to the same
lossy behavior causing a random dither-like pattern to the added
transparency (it isn't a dither though).


  Anthony Thyssen ( System Programmer )    <A.Thyssen at griffith.edu.au>
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