这个问题通过java压缩带有大图像的pdf https://stackoverflow.com/questions/20614350/compress-pdf-with-large-images-via-java给出了在 Java 中使用 iText 压缩 PDF 的代码。
由于在Android中没有Graphics2D、AffineTransform、BufferedImage和ImageIO,我想通过使用Bitmap类来修改这段代码。
UPDATE:感谢@TilmanHausherr,我将压缩修改为 JPEG 并获得了以下工作代码。
public static void manipulatePdf(String src, String dest) throws IOException, DocumentException {
// Read the file
PdfReader reader = new PdfReader(src);
int n = reader.getXrefSize();
PdfObject object;
PRStream stream;
// Look for image and manipulate image stream
for (int i = 0; i < n; i++) {
object = reader.getPdfObject(i);
if (object == null || !object.isStream())
continue;
stream = (PRStream)object;
// if (value.equals(stream.get(key))) {
PdfObject pdfsubtype = stream.get(PdfName.SUBTYPE);
System.out.println(stream.type());
if (pdfsubtype != null && pdfsubtype.toString().equals(PdfName.IMAGE.toString())) {
PdfImageObject image = new PdfImageObject(stream);
byte[] imageBytes= image.getImageAsBytes();
Bitmap bmp;
bmp = BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.length);
if (bmp == null) continue;
int width=bmp.getWidth();
int height=bmp.getHeight();
Bitmap outBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
Canvas outCanvas=new Canvas(outBitmap);
outCanvas.drawBitmap(bmp, 0f, 0f, null);
ByteArrayOutputStream imgBytes = new ByteArrayOutputStream();
outBitmap.compress(Bitmap.CompressFormat.JPEG, 50, imgBytes);
stream.setData(imgBytes.toByteArray(), false, PdfStream.BEST_COMPRESSION);
stream.put(PdfName.FILTER, PdfName.DCTDECODE);
imgBytes.close();
}
}
// Save altered PDF
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
stamper.close();
reader.close();
}
不幸的是,对于我来说,JPEG 不是一个好的选择,因为我有带有透明胶片的图像。即使我将过滤器设置为 FLATEDECODE,使用 PNG 也会生成空白图像,据我了解,这应该是 PNG 过滤器。
我对 PNG 唯一的工作代码是这样的:
public static void manipulatePdf(String src, String dest) throws IOException, DocumentException {
// Read the file
PdfReader reader = new PdfReader(src);
int n = reader.getXrefSize();
PdfObject object;
PRStream stream;
// Look for image and manipulate image stream
for (int i = 0; i < n; i++) {
object = reader.getPdfObject(i);
if (object == null || !object.isStream())
continue;
stream = (PRStream)object;
// if (value.equals(stream.get(key))) {
PdfObject pdfsubtype = stream.get(PdfName.SUBTYPE);
System.out.println(stream.type());
if (pdfsubtype != null && pdfsubtype.toString().equals(PdfName.IMAGE.toString())) {
byte[] streamBytes= PdfReader.getStreamBytes(stream);
stream.setData(streamBytes, true, PdfStream.BEST_COMPRESSION);
}
}
// Save altered PDF
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
stamper.close();
reader.close();
}
上面的代码将压缩委托给 iText,这可能足够,也可能不够。