How to Specify Image Output Format in ImageMagick

This article provides a quick overview and practical guide on how to define the output file format when using the ImageMagick convert command. You will learn the standard syntax for converting images, how to explicitly force a specific file format regardless of the file extension, and how to handle batch conversions efficiently.

The Standard Extension Method

The most common and intuitive way to specify the output format in ImageMagick is by simply changing the file extension of the target filename. ImageMagick automatically detects the desired format based on the extension you provide.

The basic syntax follows this structure:

convert input_image.ext1 output_image.ext2

• To convert a PNG to a JPEG: convert image.png image.jpg
• To convert a TIFF to a WebP: convert input.tiff output.webp

Explicitly Forcing a Format

Sometimes you may want to save a file with a non-standard extension, or ensure ImageMagick strictly interprets the format without relying on the filename. You can explicitly force the output format by prefixing the output filename with the format name followed by a colon (format:).

The syntax for explicit formatting looks like this:

convert input_image.jpg FORMAT:output_image.custom

• To force a JPEG output with a generic extension: convert photo.png jpg:new_image.data
• To ensure standard PNG encoding: convert drawing.bmp png:result.png

Specifying Format During Batch Conversions

When working with large groups of files, the mogrify command (a component of the ImageMagick suite) is often preferred over convert because it can process multiple files at once. To change the output format of an entire directory of images, use the -format flag.

• To convert all JPEG images in a folder to PNG: magick mogrify -format png *.jpg

Note for ImageMagick v7 Users: In ImageMagick version 7 and newer, the standalone convert command is replaced by the primary magick command, though convert still works as a legacy alias. The syntax remains exactly the same: magick input.png output.jpg.