Android: Converting Color Image to Grayscale

Convert a Bitmap to GrayScale in Android

Isn't that exactly what the code you're linking to does? It takes a color bitmap ("bmp"), creates a duplicate bitmap ("bm"), and then draws the color bitmap into "bm" using the filter to turn it into grayscale. From that point on, you can use "bm" as an actual grayscale bitmap and do whatever you want to do with it.

You'd need to tweak the sample a bit (it's using hard-coded sizes, you may want to just clone the size of the original bitmap), but other than that, this seems to be as ready-to-use as it gets, depending on what you want.

Converting simple image to greyscale

I found two ways while I was trying to achieve the same.

1. Using ColorMatrix

   private Bitmap androidGrayScale(final Bitmap bmpOriginal) {
       int width, height;
       height = bmpOriginal.getHeight();
       width = bmpOriginal.getWidth();
       Bitmap bmpGrayscale = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
       Canvas canvas = new Canvas(bmpGrayscale);
       Paint paint = new Paint();
       ColorMatrix colorMatrix = new ColorMatrix();
       colorMatrix.setSaturation(0);
       ColorMatrixColorFilter colorMatrixFilter = new ColorMatrixColorFilter(colorMatrix);
       paint.setColorFilter(colorMatrixFilter);
       canvas.drawBitmap(bmpOriginal, 0, 0, paint);
       return bmpGrayscale;
   }
   

2. Using OpenCV

Download OpenCV Library And Import as a Library Project. Add this library to your project as a reference library.

Download Links : OpenCV

private Bitmap openCVGrayScale(final Bitmap bmpOriginal, final String filePath) {
        Mat imgToProcess;
        Mat imgToDest = new Mat();
        imgToProcess = Highgui.imread(filePath, Highgui.CV_LOAD_IMAGE_GRAYSCALE);
        org.opencv.android.Utils.bitmapToMat(bmpOriginal, imgToProcess);
        Imgproc.cvtColor(imgToProcess, imgToDest, Imgproc.COLOR_BGR2GRAY);
        Bitmap bmpGrayscale = Bitmap.createBitmap(imgToDest.cols(), imgToDest.rows(), Bitmap.Config.ARGB_8888); 
        org.opencv.android.Utils.matToBitmap(imgToDest, bmpGrayscale);
        return bmpGrayscale;
    }

Do not forget to check in your Activity

static {
    if (!OpenCVLoader.initDebug()) {
        android.util.Log.e("TAG", "Error");
    }
}

Thanks.

Convert bitmap to Grayscale

In Android O they have introduced new Bitmap.Config the Bitmap.Config.HARDWARE which is an actual optimization when it comes to draw the Bitmap to the screen. So since you are using Software rendering that is why you get the error.

Try this:

fun getGrayScaleBitmap(original: Bitmap): Bitmap {
    // You have to make the Bitmap mutable when changing the config because there will be a crash
    // That only mutable Bitmap's should be allowed to change config.
    val bmp = original.copy(Bitmap.Config.ARGB_8888, true)
    val bmpGrayscale = Bitmap.createBitmap(bmp.width, bmp.height, Bitmap.Config.ARGB_8888)
    val canvas = Canvas(bmpGrayscale)
    val paint = Paint()
    val colorMatrix = ColorMatrix()
    colorMatrix.setSaturation(0f)
    val colorMatrixFilter = ColorMatrixColorFilter(colorMatrix)
    paint.colorFilter = colorMatrixFilter
    canvas.drawBitmap(bmp, 0F, 0F, paint)
    return bmpGrayscale
}

This will replace the Bitmap.Config from Bitmap.Config.HARDWARE to Bitmap.Config.ARGB_8888.

Hope it helps!!!

How to apply, converting image from colored to grayscale algorithm to Android?

You need to strip off the bits that aren't part of the component you're getting, especially if there's any sign extension going on in the shifts.

    int R = (q[i] >> 16) & 0xff ;     //bitwise shifting 
    int G = (q[i] >> 8) & 0xff ; 
    int B = q[i] & 0xff ; 

How to grayscale an image on imageview?

Hi you can make the image black n white using contrast.

See the code..

 public static Bitmap createContrast(Bitmap src, double value) {
// image size 
int width = src.getWidth();
int height = src.getHeight();
// create output bitmap 
Bitmap bmOut = Bitmap.createBitmap(width, height, src.getConfig());
// color information 
int A, R, G, B;
int pixel;
// get contrast value 
double contrast = Math.pow((100 + value) / 100, 2);

// scan through all pixels 
for(int x = 0; x < width; ++x) {
    for(int y = 0; y < height; ++y) {
        // get pixel color 
        pixel = src.getPixel(x, y);
        A = Color.alpha(pixel);
        // apply filter contrast for every channel R, G, B 
        R = Color.red(pixel);
        R = (int)(((((R / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
        if(R < 0) { R = 0; }
        else if(R > 255) { R = 255; }

        G = Color.red(pixel);
        G = (int)(((((G / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
        if(G < 0) { G = 0; }
        else if(G > 255) { G = 255; }

        B = Color.red(pixel);
        B = (int)(((((B / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
        if(B < 0) { B = 0; }
        else if(B > 255) { B = 255; }

        // set new pixel color to output bitmap 
        bmOut.setPixel(x, y, Color.argb(A, R, G, B));
    } 
} 

return bmOut;
 } 

Set the double value to 50 on mathod call. For Example

createContrast(Bitmap src, 50) 

For more information on formulae please refer this

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