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像素的严格限制。

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)

如何创建任意大小的图像？

加分：由于图像只有黑白两种颜色，因此一种高效的数据格式将非常好。

Answer 1

您只遇到了特定图像编写器的限制。当我尝试使用PNG时，它更适合真正的black&不管怎样，白色图像都可以写入和读取更大的图像。

我使用以下代码进行测试：

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。这种限制似乎在实现的几个地方都是硬编码的。

Answer 2

pbm可能是适合您的图像格式，而且它甚至不需要使用Java的图像库。

static void writeRandomBlackWhiteImage(
OutputStream out, long width, long height) throws IOException {
String header = String.format("P4n%dn%dn", 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);
}
}

注意(与java.awt.image.BufferedImage不同(这可以容易地产生尺寸大于Integer.MAX_VALUE的图像。(尽管处理这些图像可能很有挑战性。(