Android : 如何将压缩图像转换为最小大小的字符串
Android : How to convert the compressed images to string with minimum size
在我的 android 应用程序中,我使用类似图像压缩的 whatsapp,然后我使用 Base64 编码将压缩图像位图转换为字符串,我注意到当我压缩 5mb 图像并将其保存在另一个位置它只有 60kb 或 70kb 之类的东西,而 Base64 编码的字符串对于同一图像占用 500kb 或 600kb,为什么会这样?有什么方法可以将压缩图像转换为字符串,其相同 size.Below 是我的代码。
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;
}
此处压缩图像的大小为 60kb 或 70kb,但是当我将 strBitmap 保存到数据库时它占用 500kb 或 600kb.How 我可以将具有相同大小的压缩位图转换为字符串吗?
虽然你的图片有一个很大的不同。
您存储为文件的图像存储为 JPEG
bitmapImg.compress(Bitmap.CompressFormat.JPEG, 80, out);
而 Base64 编码的字符串是 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
也改变了两次压缩之间的内容。
在我的 android 应用程序中,我使用类似图像压缩的 whatsapp,然后我使用 Base64 编码将压缩图像位图转换为字符串,我注意到当我压缩 5mb 图像并将其保存在另一个位置它只有 60kb 或 70kb 之类的东西,而 Base64 编码的字符串对于同一图像占用 500kb 或 600kb,为什么会这样?有什么方法可以将压缩图像转换为字符串,其相同 size.Below 是我的代码。
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;
}
此处压缩图像的大小为 60kb 或 70kb,但是当我将 strBitmap 保存到数据库时它占用 500kb 或 600kb.How 我可以将具有相同大小的压缩位图转换为字符串吗?
虽然你的图片有一个很大的不同。
您存储为文件的图像存储为 JPEG
bitmapImg.compress(Bitmap.CompressFormat.JPEG, 80, out);
而 Base64 编码的字符串是 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
也改变了两次压缩之间的内容。