How can i force the imagemagick module of nodejs to output one single image only?

Question

I am using the imagemagick module with Nodejs

im  = require('imagemagick');

The imagemagick module uses the imagemagick command line tools. I use the convert method to crop an image

im.convert([image_path, '-crop', '200x150', '-gravity', 'center', target_path],
  function(err, stdout){}
);

This results in two images. The one with the cropped image area - the second with the image garbage i tried to get rid of.

How can i force imagemagick to output one image file only?

Answer 1

Per the imagemagick documentation for cropping, which is admittedly a little obtuse (emphasis added):

The width and height of the geometry argument give the size of the image that remains after cropping, and x and y in the offset (if present) gives the location of the top left corner of the cropped image with respect to the original image.

...

If the x and y offsets are present, a single image is generated, consisting of the pixels from the cropping region.

...

If the x and y offsets are omitted, a set of tiles of the specified geometry, covering the entire input image, is generated.

... so, you just need to specify your x and y offsets as part of your geometry argument, like so: 200x150-100-75

Notice that I've specified -100 and -75 for the upper left corner of your crop region, this is because you set your gravity to center, but it appears that imagemagick tries to intelligently determine the appropriate distance target based on your gravity, and I don't see exactly how it behaves when you choose center. So you may have to play around with this one a bit, or you could omit the gravity and use the actual offset from the top left corner of your original image.

Answer 2

I had to use the +delete parameter to remove the last image from the image sequence.

im.convert([image_file.path, '-crop', geometry, '+delete', thumb_path], ...