From your pseudo-code example, we understand that you want to replace the stream of an object that contains an image. There are several examples on how to do this.
For instance, in the SpecialID example, we create a PDF where we mark a specific image with a special ID. In the ResizeImage example, we track that image based on that special ID and we replace the stream:
object = reader.getPdfObject(i);
if (object == null || !object.isStream())
continue;
stream = (PRStream)object;
if (value.equals(stream.get(key))) {
PdfImageObject image = new PdfImageObject(stream);
BufferedImage bi = image.getBufferedImage();
if (bi == null) continue;
int width = (int)(bi.getWidth() * FACTOR);
int height = (int)(bi.getHeight() * FACTOR);
BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
AffineTransform at = AffineTransform.getScaleInstance(FACTOR, FACTOR);
Graphics2D g = img.createGraphics();
g.drawRenderedImage(bi, at);
ByteArrayOutputStream imgBytes = new ByteArrayOutputStream();
ImageIO.write(img, "JPG", imgBytes);
stream.clear();
stream.setData(imgBytes.toByteArray(), false, PRStream.NO_COMPRESSION);
stream.put(PdfName.TYPE, PdfName.XOBJECT);
stream.put(PdfName.SUBTYPE, PdfName.IMAGE);
stream.put(key, value);
stream.put(PdfName.FILTER, PdfName.DCTDECODE);
stream.put(PdfName.WIDTH, new PdfNumber(width));
stream.put(PdfName.HEIGHT, new PdfNumber(height));
stream.put(PdfName.BITSPERCOMPONENT, new PdfNumber(8));
stream.put(PdfName.COLORSPACE, PdfName.DEVICERGB);
}
You will find another example in the book The Best iText Questions on StackOverflow where I answered the following question: PDF Convert to Black And White PNGs
I wrote the ReplaceImage example to show how to replace the image:
public static void replaceStream(PRStream orig, PdfStream stream) throws IOException {
orig.clear();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
stream.writeContent(baos);
orig.setData(baos.toByteArray(), false);
for (PdfName name : stream.getKeys()) {
orig.put(name, stream.get(name));
}
}
As you can see, it isn't as trivial as saying:
var object = Pdf.GetObjectById("company_logo");
object.SetValue(myImage);
As I explained in my comment, this doesn't make sense:
object.SetPosition(x, y);
The objects we're manipulating are streams that are used as Image XObjects. The advantage of having Image XObjects is that they can be reused. For instance: if you have the same logo on every page, then you want to store the bytes of that image only once and reuse the same logo multiple times. This means that the object with the image bytes doesn't know anything about its position. The position is determined in the content stream. It depends on the CTM.
