imageSimilarity

imageSimilarity(before: DiffPixels, after: DiffPixels, options?: DiffImageOptions): DiffImageSimilarity

DiffImageSimilarity imageSimilarity(DiffPixels before, DiffPixels after, [DiffImageOptions? options]);

Field	What it says
similarity	How alike the two are, from 0 to 1. Times a hundred is the percentage.
identical	Whether not one pixel came out different.
pixels	How many pixels at least one of the two covers.
matched	How many of those came out the same.
changed	How many both cover and disagree about.
added	How many only the second covers.
removed	How many only the first covers.
distance	How far apart two pixels are on average, over the pixels both cover.
before	How large the first picture was.
after	How large the second one was.

The whole comparison runs underneath, so every option means what it means there. A comparison already worked out needs no second pass: 1 - result.stats.ratio is the same number.