pixelRatio property
The pixelRatio describes the scale between the logical pixels and the size of the output image. Specifying 1.0 will give you a 1:1 mapping between logical pixels and the output pixels in the image. The default is a pixel ration of 3 and a value below 1 is not recommended.
See RenderRepaintBoundary for the underlying implementation.
Implementation
final double pixelRatio;