JPEGmini adds a hidden metadata containing version information and image hash to all recompressed JPEG files.Guetzli is extremely slow requiring approximately 1 minute of CPU and 100 megabytes (MB) of memory per 1 megapixel (MPix).TinyPNG images could be losslessly compressed by 6.3% more using Optimage.TinyPNG and similar tools use stock PNGQuant at more aggressive settings, which greatly increases the likehood of a high local error in images mixing flat colored and photographic content, e.g.ImageOptim forces 4:2:0 chroma subsampling even at higher quality 92-95, which leads to noticeable image quality degradation at comparable file size.Due to global error averaging and forced 4:2:0 chroma subsampling, the local error is virtually unlimited in tools like ImageOptim and TinyPNG, regardless of quality setting.Guetzli achieved best quality/size ratio in some cases but failed to provide consistent quality especially at lower quality settings.The Guetzli score matches the results of the official study, where 75% of human ratings are in favor of Guetzli, which also implies Guetzli performed worse than the baseline JPEG encoder in 25% of cases.The human-rated scores correlate with the scores estimated by Butteraugli, which is considered a state-of-the-art image quality metric.**Butteraugli score is in multiples of just noticeable difference (JND) with a confidence level of 95%.
Hover over results to see the actual number of images. *Score shows how many images are visually indistinguishable from originals under normal viewing conditions.