图像减法的结果不正确

Question

我想逐个像素地减去两个图像以检查它们的相似程度.图像具有相同的尺寸,一个稍暗,并且在亮度旁边它们没有区别.但是我在结果中得到了那些小点.我是否减去了这两个图像？两者都是bmp文件.

import java.awt.image.BufferedImage;
import java.io.File;   
import javax.imageio.ImageIO;

public class Main2 {
    public static void main(String[] args) throws Exception {
        int[][][] ch = new int[4][4][4];
        BufferedImage image1 = ImageIO.read(new File("1.bmp"));
        BufferedImage image2 = ImageIO.read(new File("2.bmp"));
        BufferedImage image3 = new BufferedImage(image1.getWidth(), image1.getHeight(), image1.getType());
        int color;
        for(int x = 0; x < image1.getWidth(); x++)
            for(int y = 0; y < image1.getHeight(); y++) {
                color = Math.abs(image2.getRGB(x, y) - image1.getRGB(x, y));                
                image3.setRGB(x, y, color);
            }
        ImageIO.write(image3, "bmp",  new File("image.bmp"));


    }
}

图片1

图2

结果

Answer 1

这里的问题是你无法直接减去颜色.每个像素由一个int值表示.该int值由4个字节组成.这4个字节代表颜色分量ARGB,其中

A = Alpha
R = Red
G = Green
B = Blue

(Alpha是像素的不透明度,在BMP图像中始终为255(即最大值)).

因此,一个像素可以表示为

(255,0,254,0)

当你从这个像素中减去另一个像素时,如(255,0,255,0),那么第三个字节将下溢:它将变为-1.但由于这是一个整数的一部分,因此产生的颜色将是类似的

(255, 0, 254, 0) - 
(255, 0, 255, 0) = 
(255, 255, 255, 0)

因此,远离你在这种情况下的期望.

关键是您必须将颜色分成A,R,G和B组件,并对这些组件执行计算.在最一般的形式中,它可以像这样实现:

int argb0 = image0.getRGB(x, y);
int argb1 = image1.getRGB(x, y);

int a0 = (argb0 >> 24) & 0xFF;
int r0 = (argb0 >> 16) & 0xFF;
int g0 = (argb0 >>  8) & 0xFF;
int b0 = (argb0      ) & 0xFF;

int a1 = (argb1 >> 24) & 0xFF;
int r1 = (argb1 >> 16) & 0xFF;
int g1 = (argb1 >>  8) & 0xFF;
int b1 = (argb1      ) & 0xFF;

int aDiff = Math.abs(a1 - a0);
int rDiff = Math.abs(r1 - r0);
int gDiff = Math.abs(g1 - g0);
int bDiff = Math.abs(b1 - b0);

int diff = 
    (aDiff << 24) | (rDiff << 16) | (gDiff << 8) | bDiff;
result.setRGB(x, y, diff);

由于这些是灰度图像,因此这里完成的计算有些多余:对于灰度图像,R,G和B分量始终相等.由于不透明度始终为255,因此不必在此处明确处理.因此,对于您的特定情况,将其简化为足够了

int argb0 = image0.getRGB(x, y);
int argb1 = image1.getRGB(x, y);

// Here the 'b' stands for 'blue' as well
// as for 'brightness' :-)
int b0 = argb0 & 0xFF;
int b1 = argb1 & 0xFF;
int bDiff = Math.abs(b1 - b0);

int diff = 
    (255 << 24) | (bDiff << 16) | (bDiff << 8) | bDiff;
result.setRGB(x, y, diff);