Question

I am trying to display a bitmap image pixel by pixel (which explicitly means with some delay).
For that I am using two "for-loops", but it prints only a single row of pixels…

My code:

Button start = (Button) findViewById(R.id.start);
start.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        //Toast.makeText(getBaseContext(), "Printing...", Toast.LENGTH_SHORT).show();
        iImageArray = new int[bMap.getWidth()* bMap.getHeight()];                                   //initializing the array for the image size
        bMap.getPixels(iImageArray, 0, bMap.getWidth(), 0, 0, bMap.getWidth(), bMap.getHeight());   //copy pixel data from the Bitmap into the 'intArray' array  
             
        //Canvas canvas = new Canvas (bMap);
        //replace the red pixels with yellow ones  
        for (int i=0; i < bMap.getHeight(); i++) {  
            for(int j=0; j<bMap.getWidth(); j++) {
                iImageArray[j] = 0xFFFFFFFF;
            } 
        } 
        bMap = Bitmap.createBitmap(iImageArray, bMap.getWidth(), bMap.getHeight(), Bitmap.Config.ARGB_8888);//Initialize the bitmap, with the replaced color
        image.setImageBitmap(bMap);
        //canvas.drawPoints(iImageArray, 0, bMap.getHeight()*bMap.getWidth(), paint);
    }
});

And I want to print the bitmap in grayscale and for that I found this code…

public Bitmap toGrayscale(Bitmap bmpOriginal) {        
    int width, height;
    height = bmpOriginal.getHeight();
    width = bmpOriginal.getWidth();    

    Bitmap bmpGrayscale = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
    Canvas c = new Canvas(bmpGrayscale);
    Paint paint = new Paint();
    ColorMatrix cm = new ColorMatrix();
    cm.setSaturation(0);

    ColorMatrixColorFilter f = new ColorMatrixColorFilter(cm);
    paint.setColorFilter(f);

    c.drawBitmap(bmpOriginal, 0, 0, paint);

    return bmpGrayscale;
}

It is iImageArray[i] = 0xFFFFFFFF; that I have to test, not the actual grayscale value…

Answer 1

Your code looks basically correct except for your inner loop. Your comment says that you’re setting them to yellow, but you’re actually storing white. The loop will only affect the first row of pixels because your array index has a range of 0 to width-1. You can either calculate the index by multiplying (i*width+j) or keep a counter that increments.

Original Version:

//replace the red pixels with yellow ones  
for (int i=0; i < bMap.getHeight(); i++)  
{  
    for(int j=0; j<bMap.getWidth(); j++)
    {
        iImageArray[j] = 0xFFFFFFFF;
    } 
} 

Fixed Version:

//replace the red pixels with yellow ones
int iWidth = bMap.getWidth();  
for (int i=0; i < bMap.getHeight(); i++)  
{  
    for(int j=0; j<bMap.getWidth(); j++)
    {
        iImageArray[(i*iWidth)+j] = 0xFF00FFFF; // actual value of yellow
    } 
}