Viewing the difference of images

This demo shows a common example of comparing images by viewing differences through superposition.

Here, the imshowpair function is used to rotate the image.

Pkg.add(["TestImages"])

using Images
using TestImages

# Uploading a test image
img = float.(testimage("cameraman"))
# rotate the image by 4 degrees
img_r = imrotate(img, -pi/45, axes(img))

The mosaicview function allows you to display multiple images. This method is especially useful when images have different sizes and colors.

mosaicview(img, img_r; nrow=1, npad=20, fillvalue=colorant"white")

In some cases, when the differences between two images are relatively minor, a simple visual comparison may not produce the desired result.

In this case, gray images can be filled with different RGB channels, create an RGB representation, and then convert to a grayscale image.

RGB_diffview = colorview(RGB, channelview(img), channelview(img_r), fill(0., size(img)))
Gray_diffview = Gray.(RGB_diffview)

Also, two images can be compared by calculating their difference.

plain_diffview = @. img - img_r

mosaicview(plain_diffview, RGB_diffview;
           nrow=1, npad=20, fillvalue=colorant"white")

Conclusion

We have studied several ways of visual comparison, both through algebraic operations and through visual comparison. The figure above shows what these comparisons look like in a single output image.