PDFBox：将高清图像写入 PDF

Question

我正在尝试将使用 cameraa 拍摄的图像转换为 A4 PDF

    // Read image width and height
    float imageWidth = bitmap.getWidth();
    float imageHeight = bitmap.getHeight();

    // Read page width and height ignoring the margins
    float pageWidth = PDRectangle.A4.getWidth() - (margin_left_right * 2);
    float pageHeight = PDRectangle.A4.getHeight() - (margin_top_bottom * 2);

    Log.d("Image Resize", String.valueOf(imageWidth) + " x " + String.valueOf(imageHeight));
    Log.d("Image Resize", String.valueOf(pageWidth) + " x " + String.valueOf(pageHeight));

    # Image: 4160.0 x 3120.0
    # Page: 575.27563 x 821.8898

    Log.d("Image Resize", String.valueOf(requiredRatio));
    Log.d("Image Resize", String.valueOf(newImageWidth) + " x " + String.valueOf(newImageHeight));

    # Required ratio: 0.13828741
    # After scaling: 575 x 431

问题是大小为4160 x 3120 的图像，在调整为575 x 431 后，看起来非常像素化。

PDF 一般如何解决这个问题？使用contentStream.drawImage()写作时，有没有办法在600 dpi说4160 x 3120？

---

这个question 还支持这样一个事实，即如果在不调整大小等于图像高度和宽度的页面上编写，OP 只能看到 15% 的图像，应该如何缩小而不损失质量?

Answer 1

有一个重载的drawImage() 方法可以做到这一点

contentStream.drawImage(PDImageXObject, float x, float y)
contentStream.drawImage(PDImageXObject, float x, float y, float height, float width)

通过在contentStream.drawImage() 上指定明确的宽度和高度，可以实现这一点。例如，如果您想将图像显示小 4 倍但仍保持相同的分辨率，则可以使用

scaleDownRatio = 0.25;
pageSize = PDRectangle.A4;

# this will draw image at bottom left corner
PDImageXObject pageImageXObject = LosslessFactory.createFromImage(document, bitmap);
contentStream.drawImage(pageImageXObject, 0, 0, bitmap.getWidth() * ratio, bitmap.getHeight() * ratio)

# to center it you can use something like
contentStream.drawImage(pageImageXObject, (pageSize.getWidth() - bitmap.getWidth() * ratio) / 2, (pageSize.getHeight() - bitmap.getHeight() * ratio) / 2, bitmap.getWidth() * ratio, bitmap.getHeight() * ratio)