import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.media.ExifInterface;
import android.util.Base64;
import android.util.Log;
import java.io.ByteArrayOutputStream;
import 
 
java.io.IOException;
public class PicUtil {





    public static String compressImage(String filePath, String type) {

        Bitmap scaledBitmap = null;
BitmapFactory.Options options = new BitmapFactory.Options();
//      by setting this field as true, the actual bitmap pixels are not loaded in the memory. Just the bounds are loaded. If
 
//      you try the use the bitmap here, you will get null.
options.inJustDecodeBounds = true;
Bitmap bmp = BitmapFactory.decodeFile(filePath, options);
        int actualHeight = options.outHeight;
        int actualWidth = options.outWidth;
//      max Height and width values of the compressed image is taken as 816x612
 
float maxHeight = 816.0f;
        float maxWidth = 612.0f;
        float imgRatio = actualWidth / actualHeight;
        float maxRatio = maxWidth / maxHeight;
//      width and height values are set maintaining the aspect ratio of the image
if (actualHeight > maxHeight || actualWidth > maxWidth) {
            if (imgRatio < maxRatio) {
                imgRatio = maxHeight / actualHeight;
actualWidth = (int) (imgRatio * actualWidth);
actualHeight = (int) maxHeight;
} else if (imgRatio > maxRatio) {
                imgRatio = maxWidth / actualWidth;
actualHeight = (int) (imgRatio * actualHeight);
actualWidth = (int) maxWidth;
} else {
                actualHeight = (int) maxHeight;
actualWidth = (int) maxWidth;
}
        }

//      setting inSampleSize value allows to load a scaled down version of the original image
options.inSampleSize = calculateInSampleSize(options, actualWidth, actualHeight);
//      inJustDecodeBounds set to false to load the actual bitmap
options.inJustDecodeBounds = false;
//      this options allow android to claim the bitmap memory if it runs low on memory
options.inPurgeable = true;
options.inInputShareable = true;
options.inTempStorage = new byte[16 * 1024];
        try {
//          load the bitmap from its path
bmp = BitmapFactory.decodeFile(filePath, options);
} catch (OutOfMemoryError exception) {
            exception.printStackTrace();
}
        try {
            scaledBitmap = Bitmap.createBitmap(actualWidth, actualHeight, Bitmap.Config.ARGB_8888);
} catch (OutOfMemoryError exception) {
            exception.printStackTrace();
}

        float ratioX = actualWidth / (float) options.outWidth;
        float ratioY = actualHeight / (float) options.outHeight;
        float middleX = actualWidth / 2.0f;
        float middleY = actualHeight / 2.0f;
Matrix scaleMatrix = new Matrix();
scaleMatrix.setScale(ratioX, ratioY, middleX, middleY);
Canvas canvas = new Canvas(scaledBitmap);
canvas.setMatrix(scaleMatrix);
canvas.drawBitmap(bmp, middleX - bmp.getWidth() / 2, middleY - bmp.getHeight() / 2, new Paint(Paint.FILTER_BITMAP_FLAG));
//      check the rotation of the image and display it properly
ExifInterface exif;
        try {
            exif = new ExifInterface(filePath);
            int orientation = exif.getAttributeInt(
                    ExifInterface.TAG_ORIENTATION, 0);
Log.d("EXIF", "Exif: " + orientation);
Matrix matrix = new Matrix();
            if (orientation == 6) {
                matrix.postRotate(90);
Log.d("EXIF", "Exif: " + orientation);
} else if (orientation == 3) {
                matrix.postRotate(180);
Log.d("EXIF", "Exif: " + orientation);
} else if (orientation == 8) {
                matrix.postRotate(270);
Log.d("EXIF", "Exif: " + orientation);
}
            scaledBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0,
scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix,
                    true);
} catch (IOException e) {
            e.printStackTrace();
} 
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        if (type.toLowerCase().contains("png")) {
            scaledBitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
} else {
            scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos);
}

        byte[] datas = baos.toByteArray();
Log.e("size", (datas.length / 1024) + "");
        return Base64.encodeToString(datas,Base64.DEFAULT);
}


    public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;
        if (height > reqHeight || width > reqWidth) {
            final int heightRatio = Math.round((float) height / (float) reqHeight);
            final int widthRatio = Math.round((float) width / (float) reqWidth);
inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
}
        final float totalPixels = width * height;
        final float totalReqPixelsCap = reqWidth * reqHeight * 2;
        while (totalPixels / (inSampleSize * inSampleSize) > totalReqPixelsCap) {
            inSampleSize++;
}

        return inSampleSize;
}

}

一個工具類，可以使圖片壓縮最優化。質量優，檔案小。3,4M大小一般壓縮為400k。

使用方法

var ext="png"
val base64Image =  PicUtil.compressImage(pickFile?.absolutePath, ext)