@elanchezhiyan,
All the elements of the chart and the size of the image is based on the number of pixels. DPI is a measurement of “Dots per Inch” however, images are measured in pixels. Please refer to this Stackoverflow thread for more information.
If you are looking to export charts at higher resolution, you can increase the size of the chart before exporting. Please take a look at this JSFiddle for an example.
—
Thangaraj Raman
Team CanvasJS