Android:如何将压缩的图像转换为最小大小的字符串 [英] Android : How to convert the compressed images to string with minimum size
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问题描述
在我的android应用程序中，我使用的是类似图像压缩的whatsapp，然后我使用Base64编码将压缩后的图像位图转换为字符串，我注意到的是，当我压缩5mb图像并将其保存在其他位置时，其大小仅为60kb或70kb之类的东西，而Base64编码的字符串对于同一张图像却要花费500kb或600kb，为什么要这样呢?有什么办法可以将压缩后的图像转换为相同大小的字符串.下面是我的代码.
In my android application i am using whatsapp like image compression and after that i convert the compressed image bitmap to string using Base64 encoding,what i noticed is that when i compress a 5mb image and save it in another locations its just of 60kb or 70kb something like that and the Base64 encoded string is taking 500kb or 600kb for the same image, why its like that? Is there any way to convert the compressed image to string with its same size.Below is my code.
Bitmap bitmapImg;
if (requestCode == FILE_SELECT_CODE) {
if(data!= null) {
try {
Uri selectedImageUri = data.getData();
String mimeType = getContentResolver().getType(selectedImageUri);
compressImage(selectedImageUri);
// Converting compressed bitmap to string
ByteArrayOutputStream byteArrayOS = new ByteArrayOutputStream();
bitmapImg.compress(Bitmap.CompressFormat.PNG, 100, byteArrayOS);
String strBitmap = Base64.encodeToString(byteArrayOS.toByteArray(), Base64.DEFAULT);
} catch (Exception e) {
e.printStackTrace();
}
}
}
private String compressImage(Uri selImageUri) {
String fileStrName = null;
bitmapImg = null;
try {
String filePath = getRealPathFromURI(selImageUri);
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 bmpTemp = 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
bmpTemp = BitmapFactory.decodeFile(filePath, options);
} catch (OutOfMemoryError exception) {
exception.printStackTrace();
}
try {
bitmapImg = 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(bitmapImg);
canvas.setMatrix(scaleMatrix);
canvas.drawBitmap(bmpTemp, middleX - bmpTemp.getWidth() / 2, middleY - bmpTemp.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);
Matrix matrix = new Matrix();
if (orientation == 6) {
matrix.postRotate(90);
} else if (orientation == 3) {
matrix.postRotate(180);
} else if (orientation == 8) {
matrix.postRotate(270);
}
bitmapImg = Bitmap.createBitmap(bitmapImg, 0, 0, bitmapImg.getWidth(), bitmapImg.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.
bitmapImg.compress(Bitmap.CompressFormat.JPEG, 80, out);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
} catch (Exception e) {
e.printStackTrace();
}
return fileStrName;
}
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;
}
private String getRealPathFromURI(Uri 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 String getFilename() {
File file = new File(Environment.getExternalStorageDirectory().getPath(), "MyFolder/Images");
if (!file.exists()) {
file.mkdirs();
}
String uriSting = (file.getAbsolutePath() + "/" + System.currentTimeMillis() + ".jpg");
return uriSting;
}
这里压缩后的图像大小为60kb或70kb，但是当我将strBitmap保存到数据库中时，占用的大小为500kb或600kb.我如何将相同大小的压缩后的位图转换为字符串.
Here the compressed image is of size 60kb or 70kb but when I save the strBitmap to database its taking 500kb or 600kb.How can i convert the compressed bitmap with the same size to string.
推荐答案
尽管您的图片有很大的不同.
There's one big difference in your images though.
您存储为文件的图像存储为JPEG
The image you store as a file is stored as a JPEG
bitmapImg.compress(Bitmap.CompressFormat.JPEG, 80, out);
而Base64编码的字符串是PNG
while the Base64 encoded string is a PNG
bitmapImg.compress(Bitmap.CompressFormat.PNG, 100, byteArrayOS);
这可以解释大小差异.另一件事可能是bitmapImg也在两次压缩之间更改了它的内容.
This can explain the size differences. Another thing could be, that bitmapImg changed it's contents inbetween both compressions as well.
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