Paperclip: resize images without decreasing image dpi or set fixed dpi

By defaul开发者_Python百科t, the dpi of image after resizing done by paperclip is 72. I'm looking to set the dpi 300 even after the paperclip resizes the original images into thumb, medium and large. Any help please ?

Have u find the answer?Maybe u can try Setting DPI for PNG files or https://groups.google.com/forum/#!topic/paperclip-plugin/hRdKkfnNDg4.