Imagemagick: generate several files at once

Question

I use ImageMagick to generate previews. On big images(>3mb) it works really slow(for about 1-3 sec for call). Can I generate several previews at one call? I think this would be quicker.

I do this:

convert file.jpg -thumbnail 800x480 preview_800x480.jpg
convert file.jpg -thumbnail 700x400 preview_700x400.jpg
convert file.jpg -thumbnail 72x72 preview_800x480.jpg

...

And I want to do something like this:

convert file.jpg -thumbnail 800x480 preview_800x480.jpg 700x400 preview_700x400.jpg

But such command generates only last file preview_700x400.jpg. How it should be written to work properly?

Answer 1

This is using php but you do not say how you are running the code and you should be able to convert it to the method you are using.

$cmd = " file.jpg \( -clone 0 -thumbnail 800x480 -write preview_800x480.jpg +delete \)". 
" \( -clone 0 -thumbnail 700x400 -write preview_700x400.jpg +delete \) ". 
" -thumbnail 72x72 null: ";
exec("convert $cmd preview_800x480.jpg ");

Sometimes the null: causes a problem; if so try without.