Java - 从图像中获取像素数组

我只是在玩这个相同的主题，这是访问像素的最快方法。我目前知道有两种方法可以做到这一点：

1. 使用BufferedImage的方法，如@tskuzzy的答案中所述。getRGB()

2. 通过使用以下命令直接访问像素数组：

   byte[] pixels = ((DataBufferByte) bufferedImage.getRaster().getDataBuffer()).getData();
   

如果您正在处理大图像并且性能是一个问题，那么第一种方法绝对不是要走的路。该方法将 alpha、红色、绿色和蓝色值组合成一个 int，然后返回结果，在大多数情况下，您将执行相反操作来取回这些值。getRGB()

第二种方法将直接为每个像素返回红色，绿色和蓝色值，如果有alpha通道，它将添加alpha值。在计算指数方面，使用此方法更难，但比第一种方法快得多。

在我的应用程序中，我能够通过从第一种方法切换到第二种方法，将处理像素的时间减少90%以上！

以下是我设置的比较，用于比较这两种方法：

import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.io.IOException;
import javax.imageio.ImageIO;

public class PerformanceTest {

   public static void main(String[] args) throws IOException {

      BufferedImage hugeImage = ImageIO.read(PerformanceTest.class.getResource("12000X12000.jpg"));

      System.out.println("Testing convertTo2DUsingGetRGB:");
      for (int i = 0; i < 10; i++) {
         long startTime = System.nanoTime();
         int[][] result = convertTo2DUsingGetRGB(hugeImage);
         long endTime = System.nanoTime();
         System.out.println(String.format("%-2d: %s", (i + 1), toString(endTime - startTime)));
      }

      System.out.println("");

      System.out.println("Testing convertTo2DWithoutUsingGetRGB:");
      for (int i = 0; i < 10; i++) {
         long startTime = System.nanoTime();
         int[][] result = convertTo2DWithoutUsingGetRGB(hugeImage);
         long endTime = System.nanoTime();
         System.out.println(String.format("%-2d: %s", (i + 1), toString(endTime - startTime)));
      }
   }

   private static int[][] convertTo2DUsingGetRGB(BufferedImage image) {
      int width = image.getWidth();
      int height = image.getHeight();
      int[][] result = new int[height][width];

      for (int row = 0; row < height; row++) {
         for (int col = 0; col < width; col++) {
            result[row][col] = image.getRGB(col, row);
         }
      }

      return result;
   }

   private static int[][] convertTo2DWithoutUsingGetRGB(BufferedImage image) {

      final byte[] pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
      final int width = image.getWidth();
      final int height = image.getHeight();
      final boolean hasAlphaChannel = image.getAlphaRaster() != null;

      int[][] result = new int[height][width];
      if (hasAlphaChannel) {
         final int pixelLength = 4;
         for (int pixel = 0, row = 0, col = 0; pixel + 3 < pixels.length; pixel += pixelLength) {
            int argb = 0;
            argb += (((int) pixels[pixel] & 0xff) << 24); // alpha
            argb += ((int) pixels[pixel + 1] & 0xff); // blue
            argb += (((int) pixels[pixel + 2] & 0xff) << 8); // green
            argb += (((int) pixels[pixel + 3] & 0xff) << 16); // red
            result[row][col] = argb;
            col++;
            if (col == width) {
               col = 0;
               row++;
            }
         }
      } else {
         final int pixelLength = 3;
         for (int pixel = 0, row = 0, col = 0; pixel + 2 < pixels.length; pixel += pixelLength) {
            int argb = 0;
            argb += -16777216; // 255 alpha
            argb += ((int) pixels[pixel] & 0xff); // blue
            argb += (((int) pixels[pixel + 1] & 0xff) << 8); // green
            argb += (((int) pixels[pixel + 2] & 0xff) << 16); // red
            result[row][col] = argb;
            col++;
            if (col == width) {
               col = 0;
               row++;
            }
         }
      }

      return result;
   }

   private static String toString(long nanoSecs) {
      int minutes    = (int) (nanoSecs / 60000000000.0);
      int seconds    = (int) (nanoSecs / 1000000000.0)  - (minutes * 60);
      int millisecs  = (int) ( ((nanoSecs / 1000000000.0) - (seconds + minutes * 60)) * 1000);


      if (minutes == 0 && seconds == 0)
         return millisecs + "ms";
      else if (minutes == 0 && millisecs == 0)
         return seconds + "s";
      else if (seconds == 0 && millisecs == 0)
         return minutes + "min";
      else if (minutes == 0)
         return seconds + "s " + millisecs + "ms";
      else if (seconds == 0)
         return minutes + "min " + millisecs + "ms";
      else if (millisecs == 0)
         return minutes + "min " + seconds + "s";

      return minutes + "min " + seconds + "s " + millisecs + "ms";
   }
}

你能猜出输出吗？;)

Testing convertTo2DUsingGetRGB:
1 : 16s 911ms
2 : 16s 730ms
3 : 16s 512ms
4 : 16s 476ms
5 : 16s 503ms
6 : 16s 683ms
7 : 16s 477ms
8 : 16s 373ms
9 : 16s 367ms
10: 16s 446ms

Testing convertTo2DWithoutUsingGetRGB:
1 : 1s 487ms
2 : 1s 940ms
3 : 1s 785ms
4 : 1s 848ms
5 : 1s 624ms
6 : 2s 13ms
7 : 1s 968ms
8 : 1s 864ms
9 : 1s 673ms
10: 2s 86ms

BUILD SUCCESSFUL (total time: 3 minutes 10 seconds)

像这样的东西？

int[][] pixels = new int[w][h];

for( int i = 0; i < w; i++ )
    for( int j = 0; j < h; j++ )
        pixels[i][j] = img.getRGB( i, j );