Resize image to huge resolution with imagemagick

Recently I needed to print a 5-megapixel photo to roughly 1x2 meter size; the printing store wouldn't print it unless the resolution was at least 300 dpi, which, at that size, means a resolution of 500-megapixels!

Unfortunately, most image editing programs won't support so big files. One solution is to use ImageMagick from the command line. This should work in any platform supported by ImageMagick: Linux, Unix, MacOS and Windows.

First donwload and install ImageMagick from http://www.imagemagick.org.

From a terminal window, type the folowing command:

$ convert -monitor -limit memory 1GB -filter triangle input_file.jpg -resize 1000% output_file.jpg

The details of the different options can be found at http://www.imagemagick.org/script/convert.php, in short:

• convert is the ImageMagick tool that can (among many other things) resize images.
• -monitor is an option to display the progress of the operation. This is important to know what's happening, as the process may take several minutes.
• -limit memory 1GB. This limits the amount of memory used by ImageMagick Without this, the file failed to save!
• -filter triangle. This tells ImageMagick to use bilinear interpolation.
• 1000% was the resize factor I needed to produce the 300 dpi image at 1x2m, you can specify other percentage, different horizontal and vertical factors or a target width or heigth (or both) in pixels.

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