Convert to PDF data, with transcoding

def generate_pdf_ci_data(self, type_, quality):
        "Convert to PDF data, with transcoding"
        p_compdata = ffi.new('L_COMP_DATA **')
        result = lept.pixGenerateCIData(self._cdata, type_, quality, 0, p_compdata)
        if result != 0:
            raise LeptonicaError("Generate PDF data failed")
        return CompressedData(p_compdata[0])