java.lang.IllegalArgumentException：每个像素有多个组件

Question

I'm new to image processing in Java. I'm trying to compare two images with the code below and getting the message following the code. Any help is greatly appreciated. Thanks.

    BufferedImage imgOrig = ImageIO.read(new URL(imgOrigUrl));
    BufferedImage imgComp = ImageIO.read(new URL(imgCompUrl));                

    byte[] pixelsOrig = ((DataBufferByte) imgOrig.getRaster().getDataBuffer()).getData();
    byte[] pixelsComp = ((DataBufferByte) imgComp.getRaster().getDataBuffer()).getData();

    //System.out.println("Number of pixels orig:"+pixelsOrig.length);
    //System.out.println("Number of pixels comp:"+pixelsComp.length);

    ColorModel cmImgOrig = imgOrig.getColorModel();
    ColorModel cmImgComp = imgComp.getColorModel();

    int sum1 = 0;
    int sum2 = 0;
    for(int i:pixelsOrig){
        System.out.println(cmImgOrig.getGreen(i));  //ERROR OCCURS HERE
        //System.out.println(i);
    }

ERROR:

Testcase: testCompareImages(com.myapp.img.compare.service.CompareServiceTest):  Caused an ERROR
More than one component per pixel
java.lang.IllegalArgumentException: More than one component per pixel
    at java.awt.image.ComponentColorModel.getRGBComponent(ComponentColorModel.java:594)
    at java.awt.image.ComponentColorModel.getGreen(ComponentColorModel.java:675)
    at com.scottmacri.img.compare.service.CompareService.compareImages(CompareService.java:42)
    at com.scottmacri.img.compare.service.CompareServiceTest.testCompareImages(CompareServiceTest.java:45)

Answer 1

Like @Nathan Villaescusa said, the method you are using is expecting a single channel. Do you need the byte array or the color channel? If you only need color components you can do the following:

BufferedImage imgOrig = ImageIO.read(new URL(imgOrigUrl));
BufferedImage imgComp = ImageIO.read(new URL(imgCompUrl));

for (int y = 0; y < imgOrig.getHeight(); y++)
{
   for (int x = 0; x < imgOrig.getWidth(); x++)
   {
      System.out.println(imgOrig.getRGB(x, y) >> 8 & 0xff);
   }
}

where the int returned by getRGB(x, y) can be shifted to get the RGB and alpha components like so:

int a = rgb >> 32 & 0xff;
int r = rgb >> 16 & 0xff;
int g = rgb >> 8 & 0xff;
int b = rgb & 0xff;

Answer 2

It looks like that error is being thrown because your ColorSpace has more than 1 component, yet you are only passing in a single value to check.

You want to use the getGreen() method of ColorComponentModel that accepts a Object , not the one that accepts an int . I think the method one that accepts an int is for use with gray scale.

According to this answer , here is how to get pixel data using this method:

Raster r = imgOrig.getData();    
SampleModel sm = r.getSampleModel();
int width = sm.getWidth();
int height = sm.getHeight();
for (int x = 0; x < width; x++) {
    for (int y = 0; y < height; y++) {
        Object pixel = sm.getPixel(x, u, (int[])null, r.getDataBuffer());        
        System.out.println(cmImgOrig.getGreen(pixel));
    }
}