更快地从图像中提取直方图

更快地从图像中提取直方图

本文介绍了更快地从图像中提取直方图的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我正在寻找一种从图像中提取直方图数据的更快方法。
我目前正在使用这段代码,需要大约1200毫秒的6mpx JPEG图像:

I'm looking for a faster way to extract histogram data from an image.I'm currently using this piece of code that needs about 1200ms for a 6mpx JPEG image:

        ImageReader imageReader = (ImageReader) iter.next();
        imageReader.setInput(is);
        BufferedImage image = imageReader.read(0);
        int height = image.getHeight();
        int width = image.getWidth();
        Raster raster = image.getRaster();
        int[][] bins = new int[3][256];

        for (int i = 0; i < width; i++)
            for (int j = 0; j < height; j++) {
                bins[0][raster.getSample(i, j, 0)]++;
                bins[1][raster.getSample(i, j, 1)]++;
                bins[2][raster.getSample(i, j, 2)]++;

            }

您有什么建议吗?

推荐答案

你正在进行很多 getSamples 方法调用,他们反过来做电话和电话等。

You're doing a lot of getSamples method calls and they're in turn doing calls and calls etc.

我经常使用图片和 获得速度的典型技巧是直接操作底层 int [ ] (在这种情况下,您的BufferedImage必须由int []支持。)

I work often with pictures and the typical trick to gain speed is to manipulate directly the underlying int[] (in this case your BufferedImage must be backed by an int[]).

访问 int [] 然而,做一个 getRGB 可能是巨大的。当我写巨大的时候,我的意思是两个数量级(尝试在OS X 10.4和 int [x] 上做 getRGB ,你会看到性能获得)。

The difference between accessing the int[] and doing, say, a getRGB can be gigantic. When I write gigantic, I mean by as much as two orders of magnitude (try doing a getRGB on OS X 10.4 vs int[x] and you'll see the perf gain).

此外,没有任何电话三次 getSamples 。我只是检索一个与你的ARGB像素相对应的int,然后使用bitshift来获取RGB波段(你每个R,G和B组件做一个直方图吗?)。

Also, there's no call three times getSamples. I'd simply retrieve one int corresponding to your ARGB pixel and then bitshift to get the RGB bands (you're doing one histogram per R, G and B component right?).

您可以通过以下操作访问像素数组:

You can gain access to the pixels array by doing something like this:

final int[] a = ((DataBufferInt) image.getRaster().getDataBuffer()).getData();

此外,您可以使用单个循环执行您想要的操作,循环遍历所有像素。

Also you can do what you want to do with a single loop, looping over all the pixels.

而不是:

for ( int x = 0; x < width; x++ ) {
    for ( int y = 0; y < height; y++ ) {
        ....

你可以这样做:

for ( int p = 0; p < width*height; p++ ) {

现在,如果你想进入更奇怪的优化,不太可能证明你有效:

Now if you want to get into weirder optimizations, not as likely to prove effective you could:


  • 使用循环展开(迭代超过600万像素是一种罕见的情况,它可能有所帮助)

  • use loop unrolling (iterating over 6 million pixels is one of the rare case where it may help)

反转循环:for(p = width * height - 1; p> = 0; p - )

invert the loop: for ( p = width*height - 1; p >= 0; p--)

这篇关于更快地从图像中提取直方图的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

08-06 09:59