如何创建任意大小的黑白图像

Question

我想创建一个仅由黑白像素组成的任意大图像。我目前正在使用 BufferedImage。然而，这达到了 65500 像素的硬性限制。

Exception in thread "main" javax.imageio.IIOException: Maximum supported image dimension is 65500 pixels
    at java.desktop/com.sun.imageio.plugins.jpeg.JPEGImageWriter.writeImage(Native Method)
    at java.desktop/com.sun.imageio.plugins.jpeg.JPEGImageWriter.writeOnThread(JPEGImageWriter.java:1007)
    at java.desktop/com.sun.imageio.plugins.jpeg.JPEGImageWriter.write(JPEGImageWriter.java:371)
    at java.desktop/javax.imageio.ImageWriter.write(ImageWriter.java:613)
    at java.desktop/javax.imageio.ImageIO.doWrite(ImageIO.java:1628)
    at java.desktop/javax.imageio.ImageIO.write(ImageIO.java:1554)

如何创建任意尺寸的图像？

加分项：由于图像只是黑白的，因此高效的数据格式会很棒。

Answer 1

您只达到了特定图像编写器的限制。当我尝试使用更适合真正的黑白图像的 PNG 时，可以写入和读回更大的图像。

我使用了以下代码进行测试：

public static void main(String[] args) throws IOException {
    int[][] sizes = {{4000, 4000 }, {40_000, 40_000 }, {70_000, 4000 }, {700_000, 400 }};
    for(int[] size: sizes) {
        int width = size[0], height = size[1];
        System.out.println("trying " + width + " x " + height);
        BufferedImage bi=new BufferedImage(width,height,BufferedImage.TYPE_BYTE_BINARY);
        Graphics2D gfx = bi.createGraphics();
        gfx.setColor(Color.WHITE);
        gfx.fillRect(0, 0, width, height);
        gfx.setColor(Color.BLACK);
        gfx.drawOval(20, 20, width - 40 , height - 40);
        int off = Math.min(width, height) >>> 3;
        gfx.drawOval(off, off, width - off - off, height - off - off);
        gfx.dispose();

        test(bi, "PNG");
        test(bi, "GIF");
        test(bi, "JPEG");
    }
}

static void test(BufferedImage bi, String format) throws IOException {
    Path f = Files.createTempFile("test", "-out."+format);
    try {
        try { ImageIO.write(bi, format, f.toFile()); }
        catch(Throwable t) {
            System.err.println(format+": "+t);
            return;
        }
        BufferedImage read;
        try { read = ImageIO.read(f.toFile()); }
        catch(Throwable t) {
            System.err.println(format+": written, re-reading: "+t);
            return;
        }
        if(bi.getWidth() != read.getWidth() || bi.getHeight() != read.getHeight()) {
            System.err.println(format+": size changed to "
                              +read.getWidth() + " x " + read.getHeight());
            return;
        }
        if(format.equalsIgnoreCase("jpeg")) {
            // turn back to black & white, rounding away JPEG artifacts
            BufferedImage bw = new BufferedImage(
                read.getWidth(), read.getHeight(), BufferedImage.TYPE_BYTE_BINARY);
            Graphics2D gfx = bw.createGraphics();
            gfx.drawImage(read, 0, 0, null);
            gfx.dispose();
            read = bw;
        }
        for(int x = 0, w = bi.getWidth(); x < w; x++) {
            for(int y = 0, h = bi.getHeight(); y < h; y++) {
                if(bi.getRGB(x, y) != read.getRGB(x, y)) {
                    System.err.println(format+": content changed");
                    return;
                }
            }
        }
        System.out.println(format + ": sucessfully written and restored");
    }
    finally {
        Files.deleteIfExists(f);
    }
}

结果：

trying 4000 x 4000
PNG: sucessfully written and restored
GIF: sucessfully written and restored
JPEG: sucessfully written and restored
trying 40000 x 40000
PNG: sucessfully written and restored
GIF: sucessfully written and restored
JPEG: written, re-reading: java.lang.IllegalArgumentException: Invalid scanline stride
trying 70000 x 4000
PNG: sucessfully written and restored
GIF: size changed to 4464 x 4000
JPEG: javax.imageio.IIOException: Maximum supported image dimension is 65500 pixels
trying 700000 x 400
PNG: sucessfully written and restored
GIF: size changed to 44640 x 400
JPEG: javax.imageio.IIOException: Maximum supported image dimension is 65500 pixels

我无法创建宽度×高度超过 int 值范围的 BufferedImage 对象，我想。这种限制似乎在实施的几个地方被硬编码了。

Answer 2

pbm 可能是适合您的图像格式，它甚至不需要使用 Java 的图像库来处理。

static void writeRandomBlackWhiteImage(
        OutputStream out, long width, long height) throws IOException {
    String header = String.format("P4\n%d\n%d\n", width, height);
    out.write(header.getBytes(StandardCharsets.US_ASCII));

    // bytes = (width * height + 7) / 8, throwing ArithmeticException on overflow
    long bytes = Math.addExact(Math.multiplyExact(width, height), 7L) / 8L;
    while (bytes > 0) {
        byte[] data = new byte[(int) Math.min(0x4000, bytes)];
        ThreadLocalRandom.current().nextBytes(data);
        out.write(data);
        bytes -= data.size;
    }
}

public static void main(String[] args) throws IOException {
    try (OutputStream out = new FileOutputStream("out.pbm")) {
        writeRandomBlackWhiteImage(out, 65536, 65536);
    }
}

请注意（与 java.awt.image.BufferedImage 不同）这可以轻松生成尺寸大于 Integer.MAX_VALUE 的图像。（尽管处理这些图像可能具有挑战性。）

如何创建任意大小的黑白图像

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