@ROM, 你的观察力真够狠啊

@woniuren, 基本是无损的啦.你贴的原文里additional metadata, and other unneeded information,这句是说移除的非核心的内容.拿图片举例子,也就是移除exif之类的吧,而非从bmp到jpg的有损转换.后面for images, bit depth reduction is used when possible.意思是一旦检测到24bit存储的图片如果实际只是用了8bit的颜色,就会转换成8bit存储.人家也说了,图片质量应不会受转换影响.
当然这软件针对许多格式进行优化,不同格式可能会完全不同.

@Taotao,
不是无损的噢。
“FileOptimizer will remove additional metadata, and other unneeded information, so if you want to further modify the original files, remember to create a backup of them.

Optimized files, will look identical to the original ones, but internally they will be different in order to achieve the size reduction.
For images, bit depth reduction is used when possible. For instance an image encoded with 24 bit color depth could be resampled to 8 bit color depth if 256 colors of less are used. Quality should not be affected after the ransformation. ”

优化嘛。