Android位图保存无透明区域

Question

我想保存没有透明区域的位图

位图具有较大的透明像素。

所以我想删除那个

我该怎么做？

我不会添加图片所以用符号解释。

我不想裁剪功能。我希望使用过滤器

┌────────────────────────┐

│透明区域

│ ┌──────────┐

│裁剪这个
└──────────┘
└──────────────────────────┘

Answer 1

要找到位图的非透明区域，请在 x 和 y 中遍历位图并找到非透明区域的最小值和最大值。然后将位图裁剪到这些坐标。

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);
}

Answer 2

裁剪透明边框github。

public static Bitmap crop(Bitmap bitmap) {

    int height = bitmap.getHeight();
    int width = bitmap.getWidth();
    int[] empty = new int[width];
    int[] buffer = new int[width];
    Arrays.fill(empty, 0);
    int top = 0;
    int left = 0;
    int bottom = height;
    int right = width;

    for (int y = 0; y < height; y++) {
        bitmap.getPixels(buffer, 0, width, 0, y, width, 1);
        if (!Arrays.equals(empty, buffer)) {
            top = y;
            break;
        }
    }

    for (int y = height - 1; y > top; y--) {
        bitmap.getPixels(buffer, 0, width, 0, y, width, 1);
        if (!Arrays.equals(empty, buffer)) {
            bottom = y;
            break;
        }
    }

    empty = new int[height];
    buffer = new int[height];
    Arrays.fill(empty, 0);

    for (int x = 0; x < width; x++) {
        bitmap.getPixels(buffer, 0, 1, x, 0, 1, height);
        if (!Arrays.equals(empty, buffer)) {
            left = x;
            break;
        }
    }

    for (int x = width - 1; x > left; x--) {
        bitmap.getPixels(buffer, 0, 1, x, 0, 1, height);
        if (!Arrays.equals(empty, buffer)) {
            right = x;
            break;
        }
    }

    return Bitmap.createBitmap(bitmap, left, top, right - left + 1, bottom - top + 1);
}

Answer 3

我 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 抛出 IllegalArgumentException

请注意，如公认的答案所建议的，与独立阅读相比，逐行读取像素会提高很多性能。

/**
 * 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 4

按照官方文档：

The new bitmap may be the same object as source, or a copy may have been made.

在使用源位图执行 .recycle() 时应该考虑到。

Android位图保存无透明区域

Android Bitmap save without transparent area

android

crop

bitmap