Android Bitmap save without transparent area

Question

I want to save bitmap without transparent area.

Bitmap has large transparent pixel.

So i want to remove that

How can i do this?

I cant add picture so explain with symbols.

I dont want to crop function. I hope use filter

┌────────────────────────┐

│ transparent area

│ ┌────────┐

│ crop this
└────────┘
└────────────────────────┘

Answer 1

I took @Alvaro Menezes's answer and improved it as a Kotlin extension function. I tweaked it a bit, changed some variable names for better readability and it adds more fixes to the issue mentioned by @Ahamadullah Saikat that throws an IllegalArgumentException

Note that reading pixels by line improve a lot the performances against reading this independently as the accepted answer suggest.

/**
 * Trims a bitmap borders of a given color.
 *
 */
fun Bitmap.trim(@ColorInt color: Int = Color.TRANSPARENT): Bitmap {

    var top = height
    var bottom = 0
    var right = width
    var left = 0

    var colored = IntArray(width, { color })
    var buffer = IntArray(width)

    for (y in bottom until top) {
        getPixels(buffer, 0, width, 0, y, width, 1)
        if (!Arrays.equals(colored, buffer)) {
            bottom = y
            break
        }
    }

    for (y in top - 1 downTo bottom) {
        getPixels(buffer, 0, width, 0, y, width, 1)
        if (!Arrays.equals(colored, buffer)) {
            top = y
            break
        }
    }

    val heightRemaining = top - bottom
    colored = IntArray(heightRemaining, { color })
    buffer = IntArray(heightRemaining)

    for (x in left until right) {
        getPixels(buffer, 0, 1, x, bottom, 1, heightRemaining)
        if (!Arrays.equals(colored, buffer)) {
            left = x
            break
        }
    }

    for (x in right - 1 downTo left) {
        getPixels(buffer, 0, 1, x, bottom, 1, heightRemaining)
        if (!Arrays.equals(colored, buffer)) {
            right = x
            break
        }
    }
    return Bitmap.createBitmap(this, left, bottom, right - left, top - bottom)
}

Answer 2

To find the non-transparent area of your bitmap, iterate across the bitmap in x and y and find the min and max of the non-transparent region. Then crop the bitmap to those co-ordinates.

Bitmap CropBitmapTransparency(Bitmap sourceBitmap)
{
    int minX = sourceBitmap.getWidth();
    int minY = sourceBitmap.getHeight();
    int maxX = -1;
    int maxY = -1;
    for(int y = 0; y < sourceBitmap.getHeight(); y++)
    {
        for(int x = 0; x < sourceBitmap.getWidth(); x++)
        {
            int alpha = (sourceBitmap.getPixel(x, y) >> 24) & 255;
            if(alpha > 0)   // pixel is not 100% transparent
            {
                if(x < minX)
                    minX = x;
                if(x > maxX)
                    maxX = x;
                if(y < minY)
                    minY = y;
                if(y > maxY)
                    maxY = y;
            }
        }
    }
    if((maxX < minX) || (maxY < minY))
        return null; // Bitmap is entirely transparent

    // crop bitmap to non-transparent area and return:
    return Bitmap.createBitmap(sourceBitmap, minX, minY, (maxX - minX) + 1, (maxY - minY) + 1);
}