问题
我正在寻找从aBufferedImage
获取像素数据的最快方法(在formint[][]
中)。我的目标是能够使用int[x][y]
从图像中寻址pixel(x, y)
。我发现的所有方法都没有这样做(大多数返回int[]
s)。
#1 热门回答(148 赞)
我正在玩这个相同的主题,这是访问像素的最快方式。我目前知道有两种方法可以做到这一点:
- 使用BufferedImage的getRGB()方法,如@ tskuzzy的回答中所述。
- 通过直接访问像素数组:byte [] pixels =((DataBufferByte)bufferedImage.getRaster()。getDataBuffer())。getData();
如果你正在处理大型图像并且性能是个问题,那么第一种方法绝对不是可行的方法。 getRGB()
方法将alpha,red,green和blue值组合成一个int,然后返回结果,在大多数情况下,你会反过来获取这些值。
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,则会添加alpha值。使用这种方法在计算指数方面更难,但比第一种方法快得多。
在我的应用程序中,通过从第一种方法切换到第二种方法,我能够将处理像素的时间减少90%以上!
这是我设置比较两种方法的比较:
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 < 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 < 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)
#2 热门回答(20 赞)
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 );
#3 热门回答(14 赞)
我发现莫塔的回答让我的速度提高了10倍 - 所以感谢莫塔。
我已经将代码包装在一个方便的类中,该类在构造函数中获取BufferedImage并公开了一个等效的getRBG(x,y)方法,这使得它可以替代使用BufferedImage.getRGB(x,y)的代码。
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
public class FastRGB
{
private int width;
private int height;
private boolean hasAlphaChannel;
private int pixelLength;
private byte[] pixels;
FastRGB(BufferedImage image)
{
pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
width = image.getWidth();
height = image.getHeight();
hasAlphaChannel = image.getAlphaRaster() != null;
pixelLength = 3;
if (hasAlphaChannel)
{
pixelLength = 4;
}
}
int getRGB(int x, int y)
{
int pos = (y * pixelLength * width) + (x * pixelLength);
int argb = -16777216; // 255 alpha
if (hasAlphaChannel)
{
argb = (((int) pixels[pos++] & 0xff) << 24); // alpha
}
argb += ((int) pixels[pos++] & 0xff); // blue
argb += (((int) pixels[pos++] & 0xff) << 8); // green
argb += (((int) pixels[pos++] & 0xff) << 16); // red
return argb;
}
}