[magick-users] Trouble converting 300dpi jpeg to 72dpi jpeg with same size

[Anthony Thyssen]

Nicolas Dhomont on  wrote...
| Hello
| 
| 
| I'm trying to convert 300dpi CYMK jpeg to 72dpi RGB jpeg
| 
| I already manage to convert from CYMK to RGB by doing the following :
| 
| convert fromFile -antialias -colorspace RGB toFile
| 
| I'm now trying to convert from 300 dpi to 72dpi with the following :
| 
| convert -units PixelsPerInch fromFile -colorspace RGB -antialias 
| -resample 72x72 toFile
| 
| Size of toFile is reduced by a 4,16 ratio (= 300 / 72) but still in 300 
| dpi. (It means that if fromFile is 2.66inch wide, toFile is 2.08inch 
| wide for exemple). But I want exactly the opposite : a file in 72 dpi 
| with same size.
| I've also played with the -density option unsuccessfully.
| 
| As converting is quite simple with photoshop, I guess convert can do 
| same but I can't find out how.
| 
Resample is a special type of resize designed to resize the image data
for a specific output device, without changing an images real-world
size.   I do not think that is what you were after.

Use -density or better still    -set density   to change the real-world
pixel size, and thus the realworld image size without resizing the
actual image data.

See http://imagemagick.org/Usage/resize/#resample
Which I updated (and most of the resize page, and still on going) a
couple of weeks ago.


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