ImageView - get color of touched pixel

Question

I have following image, consisting of three colors (white, grey, black):

 <ImageView
        android:id="@+id/iv_colors"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:scaleType="fitStart"
        android:adjustViewBounds="true"
        android:src="@drawable/colors"
        />

On touch, I want to find out, which of these areas has been clicked - white, grey or black. I tried this approach:

final Bitmap bitmap = ((BitmapDrawable) ivColors.getDrawable()).getBitmap();
ivColors.setOnTouchListener((v, event) -> {
        int x = (int) event.getX();
        int y = (int) event.getY();
        int pixel = bitmap.getPixel(x,y);
        int redValue = Color.red(pixel);
        int blueValue = Color.blue(pixel);
        int greenValue = Color.green(pixel); 
        return false;
    });
}

However, each time, following exception occurs:

java.lang.IllegalArgumentException: x must be < bitmap.width()

As stated almost everywhere, this is the solution for my type of problem. However, it is not working in my project. Could somebody help me with this one?

Why are you getting the pixel at (0,0) rather than your touchpoint? — Morrison Chang, Apr 13 '21 at 16:30
Agree, In that approach they get the coordinate from the event `int x = (int)event.getX();` — javdromero, Apr 13 '21 at 16:32
What kind of drawable are you using? jpg, svg? Maybe if it's svg .getBitmap(); is not getting the right value and you have to decode the svg to bitmap — javdromero, Apr 13 '21 at 16:58

Ofekfarjun · Accepted Answer · 2021-04-13T18:12:48.430

It is not working because the size of the bitmap is different from the size of the ImageView

Try this,

imageView.setOnTouchListener((v, event) -> {

    int viewX = (int) event.getX();
    int viewY = (int) event.getY();

    int viewWidth = imageView.getWidth();
    int viewHeight = imageView.getHeight();

    Bitmap image = ((BitmapDrawable)imageView.getDrawable()).getBitmap();

    int imageWidth = image.getWidth();
    int imageHeight = image.getHeight();

    int imageX = (int)((float)viewX * ((float)imageWidth / (float)viewWidth));
    int imageY = (int)((float)viewY * ((float)imageHeight / (float)viewHeight));

    int currPixel = image.getPixel(imageX, imageY);

    Log.d("Coordinates", "(" + String.valueOf(Color.red(currPixel)) + ", " + String.valueOf(Color.blue(currPixel)) + ", " + String.valueOf(Color.green(currPixel)) + ") Pixel is: " + currPixel);

    return false;
});

ImageView - get color of touched pixel

1 Answers1