用Java实现Matlab的rgb2gray [英] Implementing Matlab's rgb2gray in Java
问题描述
我正在尝试根据在Java中实现Matlab的rgb2gray
http://www.mathworks.com/help/toolbox/images/ref/rgb2gray.html .我有以下代码:
I'm trying to implement Matlab's rgb2gray
in Java according to http://www.mathworks.com/help/toolbox/images/ref/rgb2gray.html . I have the following code:
public BufferedImage convert(BufferedImage bi){
int heightLimit = bi.getHeight();
int widthLimit = bi.getWidth();
BufferedImage converted = new BufferedImage(widthLimit, heightLimit,
BufferedImage.TYPE_BYTE_GRAY);
for(int height = 0; height < heightLimit; height++){
for(int width = 0; width < widthLimit; width++){
// Remove the alpha component
Color c = new Color(bi.getRGB(width, height) & 0x00ffffff);
// Normalize
int newRed = (int) 0.2989f * c.getRed();
int newGreen = (int) 0.5870f * c.getGreen();
int newBlue = (int) 0.1140f * c.getBlue();
int roOffset = newRed + newGreen + newBlue;
converted.setRGB(width, height, roOffset);
}
}
return converted;
}
现在,我确实获得了灰度图像,但是与从Matlab获得的图像相比,它太暗了. AFAIK,将图像转换为灰度的最简单方法是拥有TYPE_BYTE_GRAY类型的BufferedImage,然后仅复制TYPE_INT_(A)RGB的BufferedImage的像素.但是即使是这种方法,其图像也比Matlab的要暗,尽管灰度足够好.我还研究了使用RescaleOp
的方法.但是,无论如何我都没有在RescaleOp中设置每个像素的灰度.
Now, I do get a grayscale image but it is too dark compared to what I get from Matlab. AFAIK, the easiest way to turn an image to grayscale is have a BufferedImage of type TYPE_BYTE_GRAY and then just copy the pixels of a BufferedImage of TYPE_INT_(A)RGB. But even this method gives an image that is darker than Matlab's though grayscale decently enough. I've also looked into using RescaleOp
. However, I don't find anyway in RescaleOp to set the grayness per pixel.
作为一项附加测试,我打印了Matlab Java nad产生的图像矩阵.在Java中,我得到的像6316128 6250335 6118749 6118749 6250335 6447714在Matlab中,我得到的只有116 117 119 120 119 115(两个矩阵的前六个数字).
As an added test, I print out the image matrices produced by Java nad by Matlab. In Java, I get figures like 6316128 6250335 6118749 6118749 6250335 6447714 while in Matlab, I only get something like 116 117 119 120 119 115 (first six figures of both matrices).
如何获得类似于Matlab的输出?
How do I get an output similar to Matlab's?
推荐答案
Java中的运算符优先级指定类型转换高于乘法.您将浮点常量转换为0,所以我完全不了解您是如何获得灰度结果的.易于修复:
The operator precedence in Java specifies that type-casting is higher than multiplication. You're casting your floating-point constants to 0, so I don't understand how you're getting a grayscale result at all. Easy to fix:
int newRed = (int) (0.2989f * c.getRed());
int newGreen = (int) (0.5870f * c.getGreen());
int newBlue = (int) (0.1140f * c.getBlue());
我也将0.2989
替换为0.2990
,因为它似乎是文档中的错字.
I would also replace 0.2989
with 0.2990
as it appears to be a typo in the documentation.
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