用Java确定图像的DPI

Question

我有一个TIFF图像已经读入我的应用程序并存储在一个BufferedImage对象中.如何使用Java Advanced Imaging(JAI)API确定图像的水平和垂直DPI？我一直在环顾四周,无法找到一种直接的方法来实现这一目标.

Answer 1

这是一个完整的示例,使用标准的ImageIO API和标准元数据格式提取DPI(实际上,每mm的像素数).复杂性,我们来了...... :-P

public class DPITest {
    public static void main(String[] args) throws IOException {
        File input = new File(args[0]);

        ImageInputStream stream = ImageIO.createImageInputStream(input);
        Iterator<ImageReader> readers = ImageIO.getImageReaders(stream);

        if (readers.hasNext()) {
            ImageReader reader = readers.next();
            reader.setInput(stream);

            IIOMetadata metadata = reader.getImageMetadata(0);
            IIOMetadataNode standardTree = (IIOMetadataNode) metadata.getAsTree(IIOMetadataFormatImpl.standardMetadataFormatName);
            IIOMetadataNode dimension = (IIOMetadataNode) standardTree.getElementsByTagName("Dimension").item(0);
            float horizontalPixelSizeMM = getPixelSizeMM(dimension, "HorizontalPixelSize");
            float verticalPixelSizeMM = getPixelSizeMM(dimension, "VerticalPixelSize");

            // TODO: Convert pixelsPerMM to DPI left as an exercise to the reader.. ;-)  

            System.err.println("horizontalPixelSizeMM: " + horizontalPixelSizeMM);
            System.err.println("verticalPixelSizeMM: " + verticalPixelSizeMM);
        }
        else {
            System.err.printf("Could not read %s\n", input);
        }
    }

    private static float getPixelSizeMM(final IIOMetadataNode dimension, final String elementName) {
        // NOTE: The standard metadata format has defined dimension to pixels per millimeters, not DPI...
        NodeList pixelSizes = dimension.getElementsByTagName(elementName);
        IIOMetadataNode pixelSize = pixelSizes.getLength() > 0 ? (IIOMetadataNode) pixelSizes.item(0) : null;
        return pixelSize != null ? Float.parseFloat(pixelSize.getAttribute("value")) : -1;
    }
}

一些资料来源:

• ImageIO API指南
• ImageIO标准元数据格式
• JAI ImageIO TIFF插件(尤其是元数据格式)