如何在 android 中减小图像尺寸而不损失其质量。
我的项目中有一个 ImageView，我必须在其中放入更大尺寸的图像。
我是安卓新手。
请帮忙。
【问题讨论】：
以下代码适用于比例图像作为纵横比：
Bitmap bitmapImage = BitmapFactory.decodeFile("Your path");
int nh = (int) ( bitmapImage.getHeight() * (512.0 / bitmapImage.getWidth()) );
Bitmap scaled = Bitmap.createScaledBitmap(bitmapImage, 512, nh, true);
your_imageview.setImageBitmap(scaled);
压缩您的图像而不会像 whatsapp 一样损失质量
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(), "MyFolder/Images");
if (!file.exists()) {
file.mkdirs();
}
String uriSting = (file.getAbsolutePath() + "/" + System.currentTimeMillis() + ".jpg");
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;
}
【讨论】：
float imgRatio = (float) actualWidth / (float) actualHeight;
(actualWidth < actualHeight)，但对于横向图像，两个(imgRatio vs maxRatio) 比较需要反转。
为 CompressFile 图像创建类
public class CompressFile {
public static File getCompressedImageFile(File file, Context mContext) {
try {
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
if (getFileExt(file.getName()).equals("png") || getFileExt(file.getName()).equals("PNG")) {
o.inSampleSize = 6;
} else {
o.inSampleSize = 6;
}
FileInputStream inputStream = new FileInputStream(file);
BitmapFactory.decodeStream(inputStream, null, o);
inputStream.close();
// The new size we want to scale to
final int REQUIRED_SIZE = 100;
// Find the correct scale value. It should be the power of 2.
int scale = 1;
while (o.outWidth / scale / 2 >= REQUIRED_SIZE &&
o.outHeight / scale / 2 >= REQUIRED_SIZE) {
scale *= 2;
}
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize = scale;
inputStream = new FileInputStream(file);
Bitmap selectedBitmap = BitmapFactory.decodeStream(inputStream, null, o2);
ExifInterface ei = new ExifInterface(file.getAbsolutePath());
int orientation = ei.getAttributeInt(ExifInterface.TAG_ORIENTATION,
ExifInterface.ORIENTATION_UNDEFINED);
switch (orientation) {
case ExifInterface.ORIENTATION_ROTATE_90:
selectedBitmap = rotateImage(selectedBitmap, 90);
break;
case ExifInterface.ORIENTATION_ROTATE_180:
selectedBitmap = rotateImage(selectedBitmap, 180);
break;
case ExifInterface.ORIENTATION_ROTATE_270:
selectedBitmap = rotateImage(selectedBitmap, 270);
break;
case ExifInterface.ORIENTATION_NORMAL:
default:
break;
}
inputStream.close();
// here i override the original image file
File folder = new File(Environment.getExternalStorageDirectory() + "/FolderName");
boolean success = true;
if (!folder.exists()) {
success = folder.mkdir();
}
if (success) {
File newFile = new File(new File(folder.getAbsolutePath()), file.getName());
if (newFile.exists()) {
newFile.delete();
}
FileOutputStream outputStream = new FileOutputStream(newFile);
if (getFileExt(file.getName()).equals("png") || getFileExt(file.getName()).equals("PNG")) {
selectedBitmap.compress(Bitmap.CompressFormat.PNG, 100, outputStream);
} else {
selectedBitmap.compress(Bitmap.CompressFormat.JPEG, 100, outputStream);
}
return newFile;
} else {
return null;
}
} catch (Exception e) {
return null;
}
}
public static String getFileExt(String fileName) {
return fileName.substring(fileName.lastIndexOf(".") + 1, fileName.length());
}
public static Bitmap rotateImage(Bitmap source, float angle) {
Matrix matrix = new Matrix();
matrix.postRotate(angle);
return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(),
matrix, true);
}
}
【讨论】：
使用此代码压缩较小尺寸的位图。
BitmapFactory.Options Options = new BitmapFactory.Options();
Options.inSampleSize = 4;
Options.inJustDecodeBounds = false;
action_bitmap = BitmapFactory.decodeFile(Glob.savedImage, Options);
Glob.savedImage 是图片的字符串路径。
【讨论】：
//我们将从已经打开文件的原始图片开始
File imgFileOrig = getPic(); //change "getPic()" for whatever you need to open the image file.
Bitmap b = BitmapFactory.decodeFile(imgFileOrig.getAbsolutePath());
// original measurements
int origWidth = b.getWidth();
int origHeight = b.getHeight();
final int destWidth = 600;//or the width you need
if(origWidth > destWidth){
// picture is wider than we want it, we calculate its target height
int destHeight = origHeight/( origWidth / destWidth ) ;
// we create an scaled bitmap so it reduces the image, not just trim it
Bitmap b2 = Bitmap.createScaledBitmap(b, destWidth, destHeight, false);
ByteArrayOutputStream outStream = new ByteArrayOutputStream();
// compress to the format you want, JPEG, PNG...
// 70 is the 0-100 quality percentage
b2.compress(Bitmap.CompressFormat.JPEG,70 , outStream);
// we save the file, at least until we have made use of it
File f = new File(Environment.getExternalStorageDirectory()
+ File.separator + "test.jpg");
f.createNewFile();
//write the bytes in file
FileOutputStream fo = new FileOutputStream(f);
fo.write(outStream.toByteArray());
// remember close de FileOutput
fo.close();
}
【讨论】：
从图库中获取图像时，接受的答案可以正常工作，但是当尝试从文件管理器中获取图像时，它会失败。原因是 Uri 的格式不同，getRealPathFromURI(imageUri) 无法从中获取真实路径。
为了解决这个问题，除了copressImage() 和getRealPathFromURI() 之外，使用与接受的答案相同的方法，它们经过调整以支持从文件管理器和图库中抓取的两个图像：
public static String compressImage(Context context, Uri uri) {
String filePath = getRealPathFromURI(context, uri);
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 static String getRealPathFromURI(Context context, Uri uri) {
Uri queryUri = MediaStore.Files.getContentUri("external");
String columnData = MediaStore.Files.FileColumns.DATA;
String columnSize = MediaStore.Files.FileColumns.SIZE;
String[] projectionData = {MediaStore.Files.FileColumns.DATA};
String name = null;
String size = null;
Cursor cursor = context.getContentResolver().query(uri, null, null, null, null);
if ((cursor != null) && (cursor.getCount() > 0)) {
int nameIndex = cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
int sizeIndex = cursor.getColumnIndex(OpenableColumns.SIZE);
cursor.moveToFirst();
name = cursor.getString(nameIndex);
size = cursor.getString(sizeIndex);
cursor.close();
}
String imagePath = "";
if ((name != null) && (size != null)) {
String selectionNS = columnData + " LIKE '%" + name + "' AND " + columnSize + "='" + size + "'";
Cursor cursorLike = context.getContentResolver().query(queryUri, projectionData, selectionNS, null, null);
if ((cursorLike != null) && (cursorLike.getCount() > 0)) {
cursorLike.moveToFirst();
int indexData = cursorLike.getColumnIndex(columnData);
if (cursorLike.getString(indexData) != null) {
imagePath = cursorLike.getString(indexData);
}
cursorLike.close();
}
}
return imagePath;
}
【讨论】：
要使用 JPEG 压缩来压缩图像并像 PNG 一样保持透明度，请使用此代码。它对我有用。
Bitmap newBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());
Canvas canvas = new Canvas(newBitmap);
canvas.drawColor(Color.WHITE);
canvas.drawBitmap(bitmap, 0, 0, null);
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
newBitmap.compress(Bitmap.CompressFormat.JPEG, 50, outputStream);
【讨论】：