CODEWITHSUNDEEP
javaandroidimagematrixandroid-bitmap
activity
activity

Reputation: 2733

Flip a Bitmap image horizontally or vertically

By using this code we can rotate an image:

public static Bitmap RotateBitmap(Bitmap source, float angle) {
      Matrix matrix = new Matrix();
      matrix.postRotate(angle);
      return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), matrix, true);
}

But how can we flip an image horizontally or vertically?

Upvotes: 42

Views: 29871

Answers (6)

Kit Mak
Kit Mak

Reputation: 261

Using Kotlin and extension functions:

// To flip horizontally:
fun Bitmap.flipHorizontally(): Bitmap {
    val matrix = Matrix().apply { postScale(-1f, 1f, width / 2f, height / 2f) }
    return Bitmap.createBitmap(this, 0, 0, width, height, matrix, true)
}

// To flip vertically:
fun Bitmap.flipVertically(): Bitmap {
    val matrix = Matrix().apply { postScale(1f, -1f, width / 2f, height / 2f) }
    return Bitmap.createBitmap(this, 0, 0, width, height, matrix, true)
}

Upvotes: 16

Ahmet B.
Ahmet B.

Reputation: 1674

Just use below codes:

private fun setVerticalFlip() {
    if (binding.imgReal.scaleX == 1.0f) {
        binding.imgReal.scaleX = -1.0f
    } else {
        binding.imgReal.scaleX = 1.0f
    }
}

private fun setHorizontalFlip() {
    if (binding.imgReal.scaleY == 1.0f) {
        binding.imgReal.scaleY = -1.0f
    } else {
        binding.imgReal.scaleY = 1.0f
    }
}

Upvotes: 1

weston
weston

Reputation: 54781

Given cx,cy is the centre of the image:

Flip in x:

matrix.postScale(-1, 1, cx, cy);

Flip in y:

matrix.postScale(1, -1, cx, cy);

Altogether:

public static Bitmap createFlippedBitmap(Bitmap source, boolean xFlip, boolean yFlip) {
    Matrix matrix = new Matrix();
    matrix.postScale(xFlip ? -1 : 1, yFlip ? -1 : 1, source.getWidth() / 2f, source.getHeight() / 2f);
    return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), matrix, true);
}

Upvotes: 72

Style-7
Style-7

Reputation: 1209

Horizontal and vertical flips for Bitmap bms (source).

Matrix matrix = new Matrix();
// for horizontal flip
matrix.setScale(-1, 1);
matrix.postTranslate( bms.getWidth(),0);
// for vertical flip
matrix.setScale( 1,-1);
matrix.postTranslate( 0, bms.getHeight());
Bitmap bm = Bitmap.createBitmap( bms, 0, 0, bms.getWidth(), bms.getHeight(), matrix, true);

Upvotes: 0

Mahesh Babariya
Mahesh Babariya

Reputation: 4570

Short extension for Kotlin

private fun Bitmap.flip(x: Float, y: Float, cx: Float, cy: Float): Bitmap {
    val matrix = Matrix().apply { postScale(x, y, cx, cy) }
    return Bitmap.createBitmap(this, 0, 0, width, height, matrix, true)
}

And usage:

For horizontal flip :-

val cx = bitmap.width / 2f
val cy = bitmap.height / 2f
val flippedBitmap = bitmap.flip(-1f, 1f, cx, cy)
ivMainImage.setImageBitmap(flippedBitmap)

For vertical flip :-

val cx = bitmap.width / 2f
val cy = bitmap.height / 2f
val flippedBitmap = bitmap.flip(1f, -1f, cx, cy)
ivMainImage.setImageBitmap(flippedBitmap)

Upvotes: 10

Gabe Sechan
Gabe Sechan

Reputation: 93561

Its all about the matrix you use. To flip it around the x axes, use [[-1,0],[0, 1]]. For the y axes, use [[1,0],[0,-1]]. The important thing here is that the absolute value of the determinant is 1, so it won't scale. And the - basically inverses the location around the given axes.

Upvotes: -1

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