The WebP team performed a comparative study of three image compression methods over a random set of 1 million images. The goals of the study were to measure the compression achieved by those methods and
to analyze the trade-offs between image sizes and compression.
Three compression methods, WebP, JPEG 2000 and Re-JPEG, were applied to the 900,000 JPEG images contained in the data set. JPEG images were re-compressed with Re-JPEG so that each was as close as
possible to a target peak signal-to-noise ratio (PSNR) value. The team's
analysis was done on the images after they had been compressed.
In addition to the large scale study, the team manually inspected 100 random images and found that, in most cases, WebP provides acceptable visual quality.
WebP achieves overall higher compression than either JPEG or JPEG 2000. Gains in file size minimization are particularly high for smaller images which are the most common ones found on the web.
The data set used in the study was a collection of 1 million images randomly sampled from a repository of images crawled from the web. The following table shows the distribution of different types of images in
the data set.