用Java缩放图像

Question

public double ratioDPI() {
    int ratio = 0;
    int minimal_dpi = 300;
    int dpi = ERXProperties.intForKey("dpi.image");
    return ratio = (dpi/minimal_dpi);
}

public BufferedImage rescale(BufferedImage img) {
    int width_img = img.getWidth();
    int height_img = img.getHeight();
    double factor_width = ERXProperties.doubleForKey("factor.size.width.image.republique.francaise");
    double factor_height = ERXProperties.doubleForKey("factor.size.height.image.republique.francaise");
    return (BufferedImage) img.getScaledInstance((int)(width_img*ratio), (int)(height_img*ratio), BufferedImage.SCALE_SMOOTH);
}

Answer 1

如果您更改了图像的DPI，例如，您在将其输出到打印机时更改了大小。如果您将DPI从300增加到600，输出中的图像只占一半的宽度和一半的高度。如果你现在调整图片大小，它只会占用更多的内存，图片的质量不会更好。

对于缩放，最好使用affineTransform，这样您就可以过滤图像bilinear，这样像素化就不会那么明显了：

缩放函数：

public static BufferedImage scale(BufferedImage source, double scale, boolean bilinearFiltering){
    try{
        BufferedImage destination = new BufferedImage((int)(source.getWidth() * scale), (int)(source.getHeight() * scale), source.getType());
        AffineTransform at = new AffineTransform();
        at.scale(scale, scale);
        AffineTransformOp scaleOp = new AffineTransformOp(at, getInterpolationType(bilinearFiltering));
        return scaleOp.filter(source, destination);
        }
    catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}

private static int getInterpolationType(boolean bilinearFiltering){
    return bilinearFiltering ? AffineTransformOp.TYPE_BILINEAR : AffineTransformOp.TYPE_NEAREST_NEIGHBOR;
}