Convert an image file from one format to another using ImageMagick

Objective

To convert an image file from one format to another using ImageMagick

Scenario

Suppose that the file input.png contains a PNG-format image. You wish to convert it to a JFIF-format image called output.jpeg using ImageMagick.

Method

The method described here uses ImageMagick to convert the image. On Debian-based systems, the command-line interface to ImageMagick is provided by the package imagemagick:

apt-get install imagemagick

Conversion is performed using the convert command:

convert input.png output.jpeg

By default:

• The input format is deduced from the file content if it begins with a recognised signature. Failing that, the format is determined by the filename extension if there is one.
• The output format is chosen to match the filename extension if there is one.

Either or both of these choices can be overridden by specifying the file format explicitly:

convert png:input.png jpeg:output.jpeg

ImageMagick supports a large number of file formats, including BMP, GIF, JPEG, PNM, PNG and TIFF. A full list can be obtained using the identify command:

identify -list format

Note that some formats require additional information to be specified such as the number of bits per pixel. Also, some of the less common formats can be read but not written, or written but not read.

Testing

You can check the format of an image using the identify command:

identify output.jpeg

The first two fields of the output are the filename and the image format:

output.jpeg JPEG 641x481 641x481+0+0 DirectClass 8-bit 45.627kb

Further Reading

• ImageMagick Image Formats

• Conventions
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• Legal