Java 如何将 BufferedImage 转换为黑白？
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How to convert a BufferedImage to black and white?
提问by user2790209
How can I convert an existing colored BufferedImage to monochrome? I want the image to be completely split between only two rgb codes, black and white. So if there's a border around the image which is a lighter or darker shade of the background, and the background is being converted to white, then I want the border to be converted to white as well, and so on.
如何将现有的彩色 BufferedImage 转换为单色？我希望图像仅在两个 rgb 代码（黑色和白色）之间完全分割。因此，如果图像周围有一个边框，它是背景的较浅或较深的阴影，并且背景正在转换为白色，那么我希望边框也转换为白色，依此类推。
How can I do this?
我怎样才能做到这一点？
If its necessary to save the image / load it from disk, I can do that if necessary.
如果有必要保存图像/从磁盘加载它，我可以在必要时这样做。
Edit:Code to test this:
编辑：代码来测试这个：
package test;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.HashSet;
import javax.imageio.ImageIO;
public class Test
{
public static void main(String[] args)
{
try
{
BufferedImage img = ImageIO.read(new File("http://i.stack.imgur.com/yhCnH.png") );
BufferedImage gray = new BufferedImage(img.getWidth(), img.getHeight(),
BufferedImage.TYPE_BYTE_GRAY);
Graphics2D g = gray.createGraphics();
g.drawImage(img, 0, 0, null);
HashSet<Integer> colors = new HashSet<>();
int color = 0;
for (int y = 0; y < gray.getHeight(); y++)
{
for (int x = 0; x < gray.getWidth(); x++)
{
color = gray.getRGB(x, y);
System.out.println(color);
colors.add(color);
}
}
System.out.println(colors.size() );
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
Image used:
使用的图像：
Using this, I get the output of 24 as the last output, i.e there were 24 colors found in this image, when there should be 2.
使用这个，我得到 24 的输出作为最后一个输出，即在这个图像中发现了 24 种颜色，而应该有 2 种颜色。
采纳答案by user2790209
The solution was to use BufferedImage.TYPE_BYTE_BINARYas the type rather than TYPE_BYTE_GRAY. Using BINARY causes a pure black & white copy of the image to be created, with no colors except b & w. Not pretty looking, but perfect for things like OCR where the colors need to be exact.
解决方案是使用BufferedImage.TYPE_BYTE_BINARYas 类型而不是TYPE_BYTE_GRAY. 使用 BINARY 会创建图像的纯黑白副本，除了黑白之外没有其他颜色。看起来不漂亮，但非常适合像 OCR 这样的颜色需要精确的东西。
