Android：点击新图片，压缩并上传到服务器

Question

完成任务的最佳方式是什么？ 回答这些问题中的任何一个都可以-

1) 如何在不丢失清晰度的情况下压缩图像？

或

2) 如何在我们的应用中以低分辨率启动相机？

我知道如何通过CameraIntent点击图像，或者通过应用程序中的图库选择图像，并将其上传到服务器。 但是由于如果用高像素密度的相机点击图像可能会太大（我的 13MP 手机的相机点击 3MB 图像）但我们无法上传。我需要大小小于 300KB，最好在 150KB 到 200KB 左右，而不会失去图片的清晰度。我们在 Android 中有这方面的库吗？ 图片将是手写文字。 由于这是不可能的，我尝试将相机的分辨率手动调低到 2MP 或 VGA，即使那样图片也足够清晰。

或者，如果我们以低分辨率启动相机，也可以这样做。

Answer 1

先走你的路并调用函数

String   mImageNewPath=compressImage(imageOldPath);

mImageNewPath 是压缩图像的路径或压缩图像的新图像而不损失质量

功能在不降低质量的情况下减小尺寸

public String compressImage(String imageUri) {

    String filePath = getRealPathFromURI(imageUri);
    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();
    }

    FileOutputStream out = null;
    String filename = getFilename();
    try {
        out = new FileOutputStream(filename);

//          write the compressed bitmap at the destination specified by filename.
        scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 80, out);

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    return filename;
}

public String getFilename() {
    File file = new File(Environment.getExternalStorageDirectory().getPath(), "Visitor Management/VisitorPicture");
    if (!file.exists()) {
        file.mkdirs();
    }
    String uriSting = (file.getAbsolutePath() + "/" + "IMG_"+System.currentTimeMillis() + ".png");
    return uriSting;

    }
    private String getRealPathFromURI(String contentURI) {
    Uri contentUri = Uri.parse(contentURI);
    Cursor cursor = getContentResolver().query(contentUri, null, null, null, null);
    if (cursor == null) {
        return contentUri.getPath();
    } else {
        cursor.moveToFirst();
        int index = cursor.getColumnIndex(MediaStore.Images.ImageColumns.DATA);
        return cursor.getString(index);
    }
}

public 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;
}

Answer 2

使用以下函数将任意图像缩放到任意维度

public static BufferedImage getScaledImage(Image srcImg, int w, int h) {
        BufferedImage resizedImg = new BufferedImage(w, h, Transparency.TRANSLUCENT);
        Graphics2D g2 = resizedImg.createGraphics();
        g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
        g2.drawImage(srcImg, 0, 0, w, h, null);
        g2.dispose();
        return resizedImg;
    }

要调用该函数，请使用以下代码：

File file = new File(path);
image = ImageIO.read(file);
newImage = getScaledImage(image, int width, int height);
File outputfile = new File("background.png");
ImageIO.write(newImage, "png", outputfile);