Using the `compare` command to visually annotate the difference between two images (with examples)
Motivation
When working with images, it is often necessary to compare two images and identify the differences between them. The compare command from ImageMagick provides a simple way to generate a comparison image that visually highlights the differences between two input images. This can be useful in various scenarios such as detecting changes in images, evaluating the effectiveness of image processing techniques, or verifying the accuracy of image compression algorithms.
Example 1: Comparing two images
To compare two images and generate a difference image, we can use the following command:
compare path/to/image1.png path/to/image2.png path/to/diff.png
In this command, path/to/image1.png and path/to/image2.png are the paths of the two input images that we want to compare. path/to/diff.png is the output path of the generated difference image.
Example 2: Comparing two images using a specific metric
The compare command allows us to specify a metric to evaluate the difference between the two images. One commonly used metric is the Peak Signal-to-Noise Ratio (PSNR). To compare two images using the PSNR metric, we can use the following command:
compare -verbose -metric PSNR path/to/image1.png path/to/image2.png path/to/diff.png
In this command, the -verbose option is used to display detailed information about the comparison process. The -metric PSNR option specifies that the PSNR metric should be used to evaluate the difference between the two images.
Output
The output of the compare command is a difference image that highlights the dissimilarities between the two input images. The generated difference image path/to/diff.png will show the regions where the images differ, with the differing areas typically depicted in some shade of gray.
The difference image can be used to visually inspect and analyze the discrepancies between the two input images. By observing the contrast between the two images in the difference image, we can easily identify the areas of change. The output comparison image can also be further processed or analyzed programmatically for automated comparison tasks.
Note that the exact appearance of the difference image may vary depending on the specific options used, the content of the input images, and the chosen metric.
