Question

我希望我的应用程序上传没有大小限制的图像，但在代码中，如果图像大小超过，我想将图像大小调整为1MB。我尝试了很多方法，但是我找不到上面提到的要求的任何代码。

有一次，我试过这个：

public void scaleDown() {
    int width = stdImageBmp.getWidth();
    int height = stdImageBmp.getHeight();
    Matrix matrix = new Matrix();
    float scaleWidth = ((float) MAX_WIDTH) / width;
    float scaleHeight = ((float) MAX_HEIGHT) / height;


    matrix.postScale(scaleWidth, scaleHeight);
    stdImageBmp = Bitmap.createBitmap(stdImageBmp, 0, 0, width, height, matrix, true);

    File Image = new File("path");


    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    //compress bmp
    stdImageBmp.compress(Bitmap.CompressFormat.JPEG, 100, byteArrayOutputStream);
    byte[] byteArray = byteArrayOutputStream.toByteArray();


    imgViewStd.setImageBitmap(stdImageBmp);
    Log.d("resizedBitmap", stdImageBmp.toString());

    width = stdImageBmp.getWidth();
    height = stdImageBmp.getHeight();
    System.out.println("imgWidth" + width);
    System.out.println("imgHeight" + height);
}

Answer 1

您可以使用此代码调整位图大小和图像大小＆lt; 1MB我建议使用480x640

的分辨率

public Bitmap getResizedBitmap(Bitmap bm, int newWidth, int newHeight) {
        int width = bm.getWidth();
        int height = bm.getHeight();
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
        // CREATE A MATRIX FOR THE MANIPULATION
        Matrix matrix = new Matrix();
        // RESIZE THE BIT MAP
        matrix.postScale(scaleWidth, scaleHeight);

        // "RECREATE" THE NEW BITMAP
        return Bitmap.createBitmap(
                bm, 0, 0, width, height, matrix, false);
    }

Answer 2

如果您真的想将位图缩小到最接近给定字节数的位图，请使用以下方法。

/**
 * Method to scale the Bitmap to respect the max bytes
 *
 * @param input    the Bitmap to scale if too large
 * @param maxBytes the amount of bytes the Image may be
 * @return The scaled bitmap or the input if already valid
 * @Note: The caller of this function is responsible for recycling once the input is no longer needed
 */
public static Bitmap scaleBitmap(final Bitmap input, final long maxBytes) {
    final int currentWidth = input.getWidth();
    final int currentHeight = input.getHeight();
    final int currentPixels = currentWidth * currentHeight;
    // Get the amount of max pixels:
    // 1 pixel = 4 bytes (R, G, B, A)
    final long maxPixels = maxBytes / 4; // Floored
    if (currentPixels <= maxPixels) {
        // Already correct size:
        return input;
    }
    // Scaling factor when maintaining aspect ratio is the square root since x and y have a relation:
    final double scaleFactor = Math.sqrt(maxPixels / (double) currentPixels);
    final int newWidthPx = (int) Math.floor(currentWidth * scaleFactor);
    final int newHeightPx = (int) Math.floor(currentHeight * scaleFactor);
    Timber.i("Scaled bitmap sizes are %1$s x %2$s when original sizes are %3$s x %4$s and currentPixels %5$s and maxPixels %6$s and scaled total pixels are: %7$s",
            newWidthPx, newHeightPx, currentWidth, currentHeight, currentPixels, maxPixels, (newWidthPx * newHeightPx));
    final Bitmap output = Bitmap.createScaledBitmap(input, newWidthPx, newHeightPx, true);
    return output;
}

“示例”用法如下所示：

// (1 MB)
final long maxBytes = 1024 * 1024; 
// Scale it
final Bitmap scaledBitmap = BitmapUtils.scaleBitmap(yourBitmap, maxBytes);
if(scaledBitmap != yourBitmap){
    // Recycle the bitmap since we can use the scaled variant:
    yourBitmap.recycle();
} 
// ... do something with the scaled bitmap

Answer 3

我试图对此发表评论，但评论变得太大了。因此，我测试了许多解决方案，似乎只有两个解决方案可以给出一些结果。

让我们首先讨论Koen解决方案。它实际上是创建一个缩放的JPG

Bitmap.createScaledBitmap(input, newWidthPx, newHeightPx, true)

似乎它根本不压缩它，只是降低了分辨率。

我已经测试了这段代码，当我通过MAX_IMAGE_SIZE = 1024000时，它为我提供了来自2.33Mb原始图像的350kb压缩图像。虫子？也缺乏质量。我无法识别Google Pixel制作的A4纸质照片上的文本。

对此问题还有另一种解决方案，该解决方案虽然质量不错，但速度却很慢。一个WHILE LOOP! 基本上，您只需遍历图像大小，直到获得所需的大小

private fun scaleBitmap() {
    if (originalFile.length() > MAX_IMAGE_SIZE) {
        var streamLength = MAX_IMAGE_SIZE
        var compressQuality = 100
        val bmpStream = ByteArrayOutputStream()
        while (streamLength >= MAX_IMAGE_SIZE) {
            bmpStream.use {
                it.flush()
                it.reset()
            }

            compressQuality -= 8
            val bitmap = BitmapFactory.decodeFile(originalFile.absolutePath, BitmapFactory.Options())
            bitmap.compress(Bitmap.CompressFormat.JPEG, compressQuality, bmpStream)
            streamLength = bmpStream.toByteArray().size
        }

        FileOutputStream(compressedFile).use {
            it.write(bmpStream.toByteArray())
        }
    }
}

我认为这种方法将消耗指数时间，具体取决于图像分辨率。 9mb的图像最多需要12秒才能压缩到1mb。质量很好。您可以通过执行以下操作来降低原始位图分辨率（这似乎是一个恒定的操作）来进行调整：

options.inSampleSize = 2;

我们需要做的是以某种方式计算任何图像的compressQuality。应当对此进行数学计算，以便我们可以根据原始图像的大小或宽度+高度确定compressQuality。

如何将图像大小减小到1MB

3 个答案: