Document pdfDocument = new Document(_dataDir + "Shrinkimage.pdf");

com.aspose.pdf.optimization.OptimizationOptions optimizationOptions = new com.aspose.pdf.optimization.OptimizationOptions();

optimizationOptions.getImageCompressionOptions().setCompressImages(true);

optimizationOptions.getImageCompressionOptions().setImageQuality(50);

pdfDocument.optimizeResources(optimizationOptions);

pdfDocument.save(_dataDir + "Shrinkimage_out.pdf");