optional png quality options passed to PngQuant. you must set pngOptions.optimize=true to enable these, otherwise the original non-modified png is returned.
2 to 256. default 256.
default false. true to disable dithering
default false, which is to return the original png. if you pass true, we will optimize the png using PngQuant. smaller file size but takes longer to process
1 to 100. default 80. Instructs pngquant to use the least amount of colors required to meet or exceed the max quality.
default 0. If conversion results in quality below the min quality the image won't be compressed
default 8. (very fast). value can rage between 1 (slow) and 11 (fast and rough)