Android实时黑白阈值图像

我有一个代码,使用以下代码将具有灰色的位图转换为黑色和白色的位图：

// scan through all pixels
for (int x = 0; x < width; ++x) {                                                                                                                                                                                               
  for (int y = 0; y < height; ++y) {                                                                                                                                                                                            
    // get pixel color
    pixel = bitmap.getPixel(x,y);                                                                                                                                                                                              
    A = Color.alpha(pixel);                                                                                                                                                                                                     
    R = Color.red(pixel);                                                                                                                                                                                                       
    G = Color.green(pixel);                                                                                                                                                                                                     
    B = Color.blue(pixel);                                                                                                                                                                                                      
    int gray = (int) (0.2989 * R + 0.5870 * G + 0.1140 * B);                                                                                                                                                                    
 
    // use 128 as threshold,above -> white,below -> black
    if (gray > 128)
    gray = 255;                                                                                                                                                                                                                 
    else
    gray = 0;                                                                                                                                                                                                                   
    // set new pixel color to output bitmap
    bmOut.setPixel(x,y,Color.argb(A,gray,gray));                                                                                                                                                                      
  }
}

正如你所看到的那样,我遍历了原始位图的所有像素点,然后我将颜色的分量与给定的阈值进行比较,在这种情况下为128,然后如果它在上面我说它是白色,否则它将是一个黑色像素.

我现在想做的是一个可以改变该阈值的Spinner,然后BW图像会有所不同.

要做到这一点,我需要再次绘制所有图像,这是非常cpu的成本时间,它需要时间再次传输所有像素.

有没有办法实时使用不同的BW阈值更改图像？

有人告诉我使用GIF,然后我会做的只是改变GIF的查找表值,有人在Android上有这方面的知识吗？

解决方法

自问这个问题以来已经过了一点时间,但我碰到了这个寻找其他东西并碰巧得到了解决方案.
您可以在没有OpenCV或任何其他第三方库的情况下实现此目的,仅使用自API级别1以来的 ColorMatrixColorFilter.

以下是您可以使用的矩阵：

//matrix that changes picture into gray scale
public static ColorMatrix createGreyMatrix() {
    ColorMatrix matrix = new ColorMatrix(new float[] {
            0.2989f,0.5870f,0.1140f,0.2989f,1,0
    });
    return matrix;
}
 
// matrix that changes gray scale picture into black and white at given threshold.
// It works this way:
// The matrix after multiplying returns negative values for colors darker than threshold
// and values bigger than 255 for the ones higher. 
// Because the final result is always trimed to bounds (0..255) it will result in bitmap made of black and white pixels only
public static ColorMatrix createThresholdMatrix(int threshold) {
    ColorMatrix matrix = new ColorMatrix(new float[] {
            85.f,85.f,0.f,-255.f * threshold,0f,1f,0f
    });
    return matrix;
}

以下是如何使用它们：

BitmapFactory.Options options = new BitmapFactory.Options();
options.inScaled = false;
 
//load source bitmap and prepare destination bitmap
Bitmap pic = BitmapFactory.decodeResource(getResources(),R.drawable.thePicture,options);
Bitmap result = Bitmap.createBitmap(pic.getWidth(),pic.getHeight(),Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(result);
 
//first convert bitmap to grey scale:
bitmapPaint.setColorFilter(new ColorMatrixColorFilter(createGreyMatrix()));
c.drawBitmap(pic,bitmapPaint);
 
//then convert the resulting bitmap to black and white using threshold matrix 
bitmapPaint.setColorFilter(new ColorMatrixColorFilter(createThresholdMatrix(128)));
c.drawBitmap(result,bitmapPaint);
 
//voilà! You can now draw the result bitmap anywhere You want:
bitmapPaint.setColorFilter(null);
otherCanvas.drawBitmap(result,null,new Rect(x,x + size,y + size),bitmapPaint);

希望这会对某人有所帮助.

Android实时黑白阈值图像

解决方法

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